Does QM and classical physics create the irreversibility of time?

 At long last I’ve found a YouTube video that pretty much describes quantum mechanics (QM) as I would. In particular, the narrator (Arvin Ash) expresses the possibility that the transition from QM to classical physics provides the irreversibility of time that we all experience in everyday life. In other words, QM describes the future and classical physics describes the past. The narrator cites Lee Smolin, who actually says that QM describes the ‘present’ and classical physics describes the past. Now, I’ve read Lee Smolin’s book, The Trouble with Physics, and, from memory, he made no mention of this, so maybe this is a new idea from him (I don’t know).

My knowledge of QM is rudimentary at best, so I’m hardly one who can judge, but I’ve been thinking this way since I wrote a post called What is now? in 2015. Back then, I didn’t know that Freeman Dyson had similar ideas. A contributor to Quora, Mark John Fernee, who clearly knows a lot more than me, made a similar point about QM to classical physics being irreversible in time, and whom I quoted in a not-so-recent post.

 

Ash also explains entanglement and decoherence without getting too esoteric about it, and seems to promote the view that entanglement, in principle, could involve the whole universe. Decoherence is often explained as the ‘leaking’ of information. The important point is that decoherence (or the wavefunction collapse) comes from the quantum phenomenon interacting with other particles, that one assumes already exist.

 

The narrator conjectures at the end that the multiverse interpretation is still possible, but I’m not so sure. The whole point of MWI (multiple worlds interpretation) is supposedly that decoherence never happens, but this variation means that it still would happen, only in other universes. Sabine Hossenfelder makes a similar point in a YouTube video of her own. 

 

The other problem with MWI, as I see it, is that entanglement would necessarily incorporate a multiverse. I suspect adherents to MWI (and there are a lot of them) wouldn’t have a problem with that, but I don’t really know. Some highly respected physicists, like Sean Carroll, are advocates of MWI. I really admire Sean Carroll and he readily admits that MWI is one of his personal prejudices. I recently saw a talk he gave on ‘time’ for New Scientist, but he didn’t mention any of this. Instead, he talked about the role of entropy, including its ramifications for the evolvement of the entire universe. I’m a heretic on entropy in that I think it’s a consequence of the arrow of time, not its cause. Having said that, the low entropy state of the Universe in the beginning is still a conundrum, though gravity plays a role in increasing complexity in the Universe, in spite of entropy.

 

In another video (by Closer to Truth), Lee Smolin articulates the possibility that time and 

space may be separate after all, which I’m beginning to wonder myself. Besides, if the Universe has a boundary (or edge) in time, but not in space, that would infer that they are separate. We know that time on a cosmic scale is finite, because we can estimate the age of the Universe.

 

I believe we all live on the edge of time (all of the time), which is contentious. All physicists, that I read and listen to, argue that there is no universal now, and I’m told that to think otherwise is naive, 19^th Century thinking. They argue that Einstein’s theories of relativity rule it out, because clocks run at different rates depending on where they are in the Universe and how fast they are travelling relative to other observers. Actually, it’s dependent on how fast they are travelling relative to an observer following a geodesic in a gravitational field (in free fall or in orbit).

 

I’m well aware that different observers, in different parts of the Universe, see a different ‘now’, because they all see stars 100s or 1000s of light years from them, which means they see them at different ages. And, of course, some of those observers could hypothetically see some of the same stars at different ages, which means they all see a different ‘now’. And then, if they are in motion with respect to each other, that distorts the differences even further. For example, if you have 2 super novae occurring in the field of view of 2 spatially separated observers, they may well see them happening in opposite sequences. Notice that this is true even without relativistic effects.

 

So one shouldn’t be surprised if Einstein’s special theory of relativity tells us that simultaneity appears subjective, both in space and time, because it can be, even without relative motion. But obviously, this isn’t the case where causality is involved. Causality insists on a sequence in time by definition, and it has to be objective, irrespective of what observers see.

 

I like to look at the famous twin paradox, because I think it contains almost everything we need to know about the special theory of relativity. I know it’s a thought experiment, but real experiments done with atomic clocks and aeroplanes and satellites tell us it’s true. The important point is the end result – when the spacefaring twin returns, they are younger than their Earthbound twin. The same effect could be made by the twin travelling near the event horizon of a black hole, which was the premise for Chris Nolan’s movie, Interstellar (which had Kip Thorne as a consultant).

 

But here’s the thing: both twins agree on what time it is in the 4-dimensional spacetime of the Universe. So, 2 observers travelling along different paths can measure different durations of time by whatever means they have, but when they reunite, they agree on where they are in time, in the same way they agree on where they are in space. I can’t see how this is possible if there isn’t a universal ‘clock’, which is arguably the edge of time for the whole universe.

Addendum 1: Mark John Fernee, whom I reference in the main text, and has a PhD in physics, proposes a similar, if not better, argument than I do. He also gives the same explanation of entropy as an 'emergent' property through probabilities that I do in other posts. However, I expect he may not agree with me that there is a 'universal now'. This is his answer to, How did entropy become associated with time?

 

 Addendum 2: Another post by Mark John Fernee (8Aug22) gives an excellent synoptic description of the relationship between classical physics and QM, which reflects my own point-of-view.

Reality, nature, the Universe and everything abhors a contradiction

 People used to say that ‘nature abhors a vacuum’, which is more often than not used metaphorically. Arguably, contradiction avoidance is more fundamental in that you don’t even need a universe for it to be requisite. Many mathematical proofs are premised on the unstated axiom that you can’t have a contradiction - reductio ad absurdum.

However, the study of physics has revealed that nature seems to love paradoxes and the difference between a paradox and a contradiction is often subtle and sometimes inexplicable. So, following that criterion, I believe that reality exists in that sliver of possibility between paradox and contradiction.

 

Clifford A Pickover, who normally writes about mathematics and physics, wrote an entertaining and provocative book, The Paradox of God and the Science of Omniscience. One of the conclusions that I took from that book is that there are rules of logic that even God can’t break. And one of those rules is the rule of contradiction that something can’t ‘be’ and ‘not be’ at the same time. It turns the argument on its head that God created logic. 

 

It’s obvious to anyone who reads this blog that I’m unceasingly fascinated by science and philosophy, and, in particular, where they meet and possibly crossover. So an unerring criterion for me is that you can’t have a contradiction. My recent exposition on the famous twin paradox demonstrates this. It can only be resolved if one accepts that only one twin experiences time dilation. If they both did, you would arrive at a contradiction, both mathematically and conceptually. Specifically, each twin would perceive the other one as younger, which is impossible. 

 

The opposite to contradiction is consistency, and if you look at the mathematical analysis of the twin paradox, you’ll see it’s consistent throughout for both twins.

 

To give another example, physicists tell us that time does not flow (as Paul Davies points out in this presentation, 48.30min mark), yet we all experience time ‘flowing’. Davies and I agree that the sensation we have of time ‘flowing’ is a psychological experience; we disagree on how or why that happens. 

 

Time is a dimension determined by the speed of light. Everything is separated, not only spatially, but also in time, because it takes a finite time for light to travel between events separated in space. This leads to the concept of spacetime, which is invariant for different observers, while space and time (independently) can be ‘measured’ to be different for different observers. Spacetime is effectively an extension of Pythagoras’s theorem into 4 dimensions, only it involves negatives.

Δs² = c²Δt² - Δx² - Δy² - Δz²

So Δs is the ‘interval’ that remains invariant, and cΔt is the time dimension converted into a spatial dimension, otherwise the equation wouldn’t work. But note that it’s c (the constant speed of light) that makes time a dimension, and it’s one of the dimensions of the Universe as a whole. Einstein’s equations work for the entire Universe, which is his greatest legacy.

 

I’ve been reading Brian Greene’s The Fabric of the Cosmos (2004), which I came across while browsing in a bookshop and bought it on impulse – I’m glad I did. It’s a 500 page book, covering all the relevant topics on cosmology, so it’s very ambitious, but also very readable.

 

Theories of gravity started with Newton, and he came up with a thought experiment that was still unresolved when Einstein revolutionised his theory. Greene discusses it in some detail. If you take a bucket of water and hang it from a rope, then turn the bucket many times so that the rope is twisted. When you release the rope the bucket spins and the water surface becomes concave in the bucket due to the centrifugal force. The point is, what is the reference frame that the bucket is spinning to? Is it the Universe as a whole? Newton would have argued that it was spinning relative to absolute space.

 

Now imagine that you could do this experiment in space; only, instead of a bucket of water, you have 2 rocks tied together. You could do it on the space station. As you spin them, you’d expect the rope or cord between them to tension. So again, what are they spinning in reference to? Greene gives a detailed historical account because it involves Mach’s principle. But in the end, when Einstein applied his theories of relativity, he came to the conclusion that they spin relative to spacetime. While we don’t have absolute space and absolute time, we have absolute spacetime, according to Einstein.

 

Why have I taken so much trouble to describe this? Because there is a frame of reference that is used to determine what direction and what speed our solar system travels in the context of the overall Universe. And it’s the Cosmic Microwave Background Radiation. Paul Davies described this in his book, About Time (1995). By measuring the difference in the Doppler effect (for CMBR) in different regions of the sky, we can deduce we are travelling in the direction of the Pisces constellation. Greene also points this out in his book.

 

All physicists that I’ve read, or listened to, argue that ‘now’ is totally dependent on the observer. They will tell you that if you move backwards and forwards here on Earth, then the time changes on some far off constellation will be in the order of hundreds of years because of the change in angle of the time slice across that part of the Universe. Greene himself explains this in a video, as well as in his book. But there is an ‘age’ for the Universe, so you have an implicit contradiction. Greene is the only person I’ve read who actually attempts to address this, though not very satisfactorily (for me).

 

But one doesn’t need to look at far off galaxies, one can look at Einstein’s original thought experiment involving 2 observers: one on a train and one on a platform. The reason physicists argue that there is no objective now is because simultaneity is different according to different observers, and Einstein uses a train as a thought experiment to demonstrate this.

 

If you have a light source in the centre of a moving carriage then a person in the carriage will observe that it gets to both ends at the same time. But a person on the platform will see that the back of the train will receive the light before the front of the train. However, the light source is moving relative to the observer on the platform, so they will see a Doppler shift in the light showing that it is moving relative to them. I contend that only the observer in the same frame of reference as the light source sees the true simultaneity. In other words, I argue that you can have 'true simultaneity' in the same way as you can have ‘true time’. Also, what many people don’t realise, that different observers not only see simultaneity happening at different times but different locations, as this video demonstrates.

 

I’m a subscriber to Quora, mainly because I get to read posts by lots of people in various fields, most of whom are more knowledgeable than me. In fact, I claim my only credential is that I read a lot of books by people much smarter than me. One of the regular contributors to Quora is Viktor T Toth, whom I’ve referenced before, and who calls himself a ‘part-time physicist’. Toth knows a lot about cosmology, QFT (quantum field theory) and black holes. He occasionally shows his considerable mathematical abilities in dealing with a question, but most of the time keeps them in reserve. What I like about Toth, is not just his considerable knowledge, but his no-nonsense approach. He doesn’t pretend or bluff; he has no problem admitting what he doesn’t know and is very respectful to his peers, while not tolerating fools.

 

Toth points out that while 2 observers can experience different durations in time (like the twins in the twin paradox) they agree on the time when they meet again. In other words, there is a time reference (like a space reference) that’s independent of the path they took to get there. As I pointed out in my post explaining relativity based on waves, it’s not only the time duration that 2 observers disagree on, but also the space duration. If someone was able to travel so fast that they could cross the galaxy in years instead of thousands of years, then they would also traverse a much shorter distance (according to them). In other words, not only does time shrink, but so does distance. We don’t tend to think that space can be just as rubbery as time.

 

And this brings me to a point that Toth and Greene seem to disagree on. Toth is adamant that space is not an entity but just the ‘distance’ between physical objects. Regarding the expanding universe, he says ‘space’ does not ‘stretch’ but it’s just that the ‘distance’ between ‘objects’ increases. Greene would probably disagree. Greene argues that wavelengths of light lengthen as space ‘stretches’.

 

What do I think? I tend to side with Greene. I think space is an entity because it has dimensions. John Barrow, in his book, The Constants of Nature, gives an excellent account of how a universe that didn’t exist in 3 dimensions would be virtually unworkable. In particular, the inverse square law for gravity, that keeps planets in stable orbits for hundreds of millions of years, would not work in any other dimensional universe.

 

But also, space can be curved by gravity, or more specifically, spacetime, as Toth readily acknowledges. I’ll return to Toth’s specific commentary on gravity and black holes later.

 

I’ve already mentioned that Greene discussed the age of the Universe. I recently did an online course provided by New Scientist on The Cosmos, and one of the lecturers was Chris Impey, Distinguished Professor, Department of Astronomy, University of Arizona. He made the point that the Universe has an ‘edge in time’, but not an edge in space. Greene expanded on this, by pointing out that everywhere in the Universe all clocks are ‘in synchronicity’, which contradicts the notion that there is no universal now. I’ll quote Greene directly on this, because it’s an important point. According to Greene (but not only Greene) whether an observer is moving away from a distant stellar object, or towards it, determines whether they would see into that object’s distant past or distant future. Mind you, because they are so far away, the object’s future is still in our past.

 

Each angled slice intersects the Universe in a range of different epochs and so the slices are far from uniform. This significantly complicates the description of cosmic history, which is why physicists and astronomers generally don’t contemplate such perspectives. Instead, they usually consider only the perspective of observers moving solely with the cosmic flow...

 

I don’t know the mathematics behind this, but I can think of an analogy that we all observe every day. You know when you walk along a street with the Sun low in the sky, so it seems to be moving with you. It will disappear behind a building then appear on the other side. And of course, another observer in another town will see the Sun in a completely different location with respect to their horizon. Does this mean that the Sun moved thousands of miles while you were walking along? No, of course not. It’s all to do with the angle of projection. In other words, the movement in the sky is an illusion, and we all know this because it happens all the time and it happens in sync with our own movements. I remember once travelling in a car with a passenger and we could see a plane low in the sky through the windscreen. My passenger commented that the plane was travelling really fast, and I pointed out that if we stopped, we’d find that the plane would suddenly slow down to a speed more commensurate with our expectations.

 

I think the phenomenon that Greene describes is a similar illusion, only we conjure it up mathematically. It makes sense to ignore it, as astronomers do (as he points out) because we don’t really expect it happens in actual fact.

 

Back in 2016, I wrote a post on a lecture by Allan Adams as part of MIT Open Courseware (8.04, Spring 2013) titled Lecture 6: Time Evolution and the Schrodinger Equation. This was a lecture for physics students, not for a lay audience. I found this very edifying, not least because it became obvious to me, from Adams’ exposition, that you could have a wave function with superposition as described by Schrodinger’s equation or you could have an observed particle (like an electron) but you couldn’t have both. Then I came across the famous quote by William Lawrence Bragg:

Everything that has already happened is particles, everything in the future is waves. The advancing sieve of time coagulates waves into particles at the moment ‘now’.

 

In that post on Adams’ lecture, I said how people (like Roger Penrose, among others) explained that ‘time’ in the famous time dependent Schrodinger equation exists outside the hypothetical Hilbert space where the wave function hypothetically exists. And it occurred to me that maybe that’s because the wave function exists in the future. And then I came across Freeman Dyson’s lecture and his unorthodox claim:

 

... the “role of the observer” in quantum mechanics is solely to make the distinction between past and future...

What really happens is that the quantum-mechanical description of an event ceases to be meaningful as the observer changes the point of reference from before the event to after it. We do not need a human observer to make quantum mechanics work. All we need is a point of reference, to separate past from future, to separate what has happened from what may happen, to separate facts from probabilities.

The inherent contradictions in attempting to incorporate classical physics into quantum mechanics (QM) disappear, if one is describing all the possible future paths of an event while the other describes what actually happened.

 

Viktor Toth, whom I’ve already mentioned, once made the interesting contention that the wave function is just a ‘mathematical construct’ (his words) and he’s not alone. He also argued that the ‘decoherence’ of the wave function is never observed, which infers that it’s already happened. Toth knows a great deal about QFC (and I don’t) but, if I understand him correctly, the field exists all the time and everywhere in spacetime.

 

Another contributor on Quora, whom I follow, is Mark John Fernee (PhD in physics, University of Queensland), who obviously knows a great deal more than me. He had this to say about ‘wave function collapse’ (or decoherence) which corroborates Toth.

 

The problem is that there is no means to detect the wavefunction, and consequently no way to detect a collapse. The collapse hypothesis is just an inference that can't be experimentally tested.

 

And, in a comment, he made this point:

 

In quantum mechanics, the measurement hypothesis, which includes the collapse of the wave function, is an irreversible process. As we perceive the world through measurements, time will naturally seem irreversible to us.

 

And I’ve made this exact same point, that we also get the ‘irreversibility’ or asymmetry between past and future, from QM physics becoming classical physics.

 

Dyson is also contentious when it comes to gravity and QM, arguing that we don’t need to combine them together and that, even if the graviton existed, it’s impossible to detect. Most physicists argue that we need a quantum gravity – that it’s the ‘missing link’ in a TOE (Theory of Everything).

 

It’s occurred to me that maybe the mathematics is telling us something when it appears obstructive to marrying general relativity with QM. Maybe they don’t go together, as Dyson intimated.

 

Again, I think Toth gives the best reasoning on this, as I elaborated on in another post.

 

We can do quantum field theory just fine on the curved spacetime background of general relativity.

Then he adds this caveat:

What we have so far been unable to do in a convincing manner is turn gravity itself into a quantum field theory.

 

Toth explains how and why they are ‘incompatible’, though he loathes that term, because he doesn’t think they’re incompatible at all.

 

Basically, Einstein’s field equations are geometrical, whereby one side of the equation gives the curvature of spacetime as a consequence of the energy, expressed on the other side of the equation. The energy, of course, can be expressed in QM, but the geometry can’t. 

 

Someone else on Quora, Terry Bollinger (retired Chief Scientist), explains this better than me:

 

It all goes back to that earlier point that GR is a purely geometric theory, which in turn means that the gravity force that it describes is also specified purely in terms of geometry. There are no particles in gravity itself, and in fact nothing even slightly quantum. Instead, you assume the existence of a smooth fabric called spacetime, and then start bending it. From that bending emerges the force we know as gravity.

 

Bollinger wrote a lengthy polemic on this, but I will leave you with his conclusion, because it is remarkably similar to Toth’s.

 

Even if you finally figure out a clever way to define a gravity-like quantum force that allows objects in spacetime to attract each other, what are those force particles traveling across?

 

He provides his own answer:

 

Underneath the quantum version, since like all of the other forces in the Standard Model this swarm-like quantum version of a gravity must ride on top of spacetime. (Emphasis in the original)

 

In other words, Bollinger claims you’ll have a redundancy: a quantum field gravity on top of a spacetime gravity. Spacetime provides the ‘background’ to QFT that Toth described, which doesn’t have to be quantum.

 

So what about quantum gravity that is apparently needed to explain black holes?

 

There is an inherent contradiction in relation to a black hole, and I’m not talking about the ‘information paradox’. There is a debate about whether information (meaning quantum information) gets lost in a black hole, which contradicts the conservation of quantum information. I’m not going to get into that as I don’t know enough about it.

 

There is a more fundamental issue: according to Toth (but not only Toth) the event horizon of a black hole is always in an observer’s future. Yet for someone at the event horizon, they could cross over it without even knowing they had done so, especially if it was a really big black hole and the tidal effects at the event horizon weren’t strong enough to spaghettify them. Of course, no one really knows this, because no one has ever been anywhere near a black hole event horizon.

 

The point is that, at the event horizon of a black hole, time stops according to an external observer, which is why, theoretically it’s always in their future. Toth makes this point many times. So, basically, for someone watching something fall into a black hole, it becomes frozen in time (at the event horizon). In fact, the Russian term for a black hole is ‘frozen star’.

 

What we can say is that light from any object gets red-shifted so much that it disappears even before it reaches the event horizon. But what about an observer at or near the event horizon looking back out at the Universe. Now, I don’t see any difference in this scenario to the twin paradox, only it’s in extremis. The observer at the event horizon, or just outside it, will see the whole universe pass by in their lifetime. Because, if they could come back and meet up with their twin, their twin would be a hologram frozen in time, thousands of years old. Now, Toth makes the point, that as far as an observer at or near the event horizon, the speed of light is still constant for them, so how can that be?

 

There is another horizon in the Universe, which is the theoretical and absolute practical limit that we can see. Because the Universe is expanding, there is a part of the Universe that is expanding faster than light, relative to us. Now, you will say, how is that possible? It’s possible because space can travel faster than light. Now Toth will confirm this, even though he claims space is not an entity. Note that some other observer in a completely different location, would see a different horizon, in the same way that sailors in different locations in the same ocean see different horizons.

 

So, a hypothetical observer, at the horizon of the Universe (with respect to us) would still see the speed of light as c relative to their spacetime. Likewise, an observer at the event horizon of a black hole also sees light as c relative to their spacetime.

 

Now most black holes, we assume, are spinning black holes and they drag an accretion disk around with them. They also drag space around with them. Is it possible then that the black hole drags space along with an observer across the event horizon into the black hole? I don’t know, but it would resolve the paradox. According to someone on Quora, Leonard Susskind argues that nothing ever crosses the event horizon, which is how he resolves the quantum information paradox.

 

This is a very lengthy post, even by my standards, but I need to say something quickly about entanglement. There appears to be a contradiction between relativity and entanglement, but not in practical terms. If there is a universal 'now', implicit in the Universe having an ‘edge in time’ (but not in space) and if QM describes the future, then entanglement is not a mystery, because it’s a correlation between events separated in space, but not in time. 

 

Entanglement involves a ‘decoherence’ in the wave function that predicts the state of a decoherence in the particle it’s entangled with, because they share the same wave function. Schrodinger understood this better than anyone else, because he realised that entanglement was an intrinsic consequence of the wave function. He famously said that entanglement was the defining characteristic of quantum mechanics.

 

But there is no conflict with relativity because the entangled particles, whatever they are, can’t be separated at any greater rate than the speed of light. However, when the correlation occurs, it appears to happen instantaneously. But this is no different to a photon always being in the future of whatever it interacts with, even if it crosses the observable universe. However, for someone who detects such a photon, they instantaneously see something in the distant past as if there has been a backward-in-time connection to its source.

 

There is no reason to believe that anything I’ve said is true and correct. I’ve tried to follow a simple dictum that nature abhors a contradiction and apply it to what I know about the Universe, while acknowledging there are lots of people who know a great deal more than me, who probably disagree.

 

I see myself as an observer on the boundary line of the history of ideas. I try to make sense of the Universe by reading and listening to people much cleverer than me, including people I have philosophical differences with.

Addendum 1: I referenced Paul Davies 1995 book, About Time; Einstein's Unfinished Revolution. I mentioned that Earth is travelling relative to the CMBR towards Pisces (at 350 km/s), and according to Davies:

This is about 0.1 percent of the speed of light, and the time-dilation factor is only about one part in a million. Thus, to an excellent approximation, Earth's historical time coincides with cosmic time, so we can recount the history of the universe contemporaneously with the history of the Earth, in spite of the relativity of time. Similar hypothetical clocks could be located everywhere in the universe, in each case in a reference frame where the cosmic background heat radiation looks uniform... we can imagine the clocks out there, and legions of sentient beings dutifully inspecting them. This set of imaginary observers will agree on a common time scale and a common set of dates for major events in the universe, even though they are moving relative to each other as a result of the general expansion of the universe. They could cross-check dates and events by sending each other data by radio; everything would be consistent. So cosmic time as measured by this special set of observers constitutes a type of universal time... It is the existence of this pervasive time scale that enables cosmologists to put dates to events in cosmic history - indeed, to talk meaningfully at all about "the universe" as a single system. (my emphasis)

Addendum 2: This is a PBS video, which gives the conventional physics view on time. I don't know who the presenter is, but it would be fair to say he knows more about this topic than me. He effectively explains Einstein's 'block universe' and why 'now' is considered totally subjective. Remember Einstein's famous words in a letter to the mother of a friend who had died:

We physicists know that the past, present and future is only a stubbornly persistent illusion.

This was a consequence of simultaneity being different for different observers, as I discussed in the main text, and is described in the video. It's important to point out that this does not undermine causality, so it refers to events that are not causally related. The video presenter goes on to point out that different observers will see different pasts and different futures on worlds far far away, dependent on their motion on this world. This infers that all events are predetermined, which is what Einstein believed, and explains why so many physicists claim that the Universe is deterministic. But it contradicts the view, among cosmologists, that the Universe has an 'edge in time but not in space'.

It's certainly worth watching the video. Curiously, his logic leads him to the conclusion that we live in a quantum multiverse (the many worlds interpretation of QM). I agree with him that different observers in different parts of the Universe must have different views of 'Now'. That's just a logical consequence of the finite speed of light. Motion then distorts that further, as he demonstrates. My view is that what we perceive is not necessarily what actually 'is'. If one looks at the clock of a moving observer their time is dilated compared to ours, and likewise they see our clocks showing time dilation compared to them. But logic tells us that they both can't be right. The twin paradox is resolved only if one acknowledges that time dilation is an illusion for one observer but not the other. And that's because one of the twin travels relative to an absolute spacetime if not an absolute space or an absolute time.

Back to the video, my contention is that one observer can't see another observer's future, even though we can see another observer's 'present' in our 'past'; I don't find that contentious at all.

My interpretation of QM, so not orthodox

This is another answer I wrote on Quora. I’ve forgotten the question, but the answer is self-explanatory. It doesn’t cover anything new (from me) but it’s more succinct than other posts I’ve written.

I’m not a physicist, but I’m well read in this area and quantum mechanics (QM) has a particular fascination for me.

Someone did a survey at a conference and, from memory, the most popular was still Bohr’s so-called Copenhagen interpretation, which many now call ‘the shut up and calculate school’. I think most physicists no longer believe that consciousness is required to ‘observe’ the outcome of a quantum experiment (like the famous double slit experiment). 

Schrodinger’s famous cat thought experiment was to demonstrate how absurd that is. In his book, What is Life?, Schrodinger asks rhetorically where does the quantum effect become ‘real’. Does it occur in the optic nerve going to the brain? Or does it occur before then or when the person has their ‘Aha’ moment? Most people would now say it happens at the apparatus level, when the isotope decays, even before it affects the cat. 

One of the most popular interpretations seems to be the multiple worlds interpretation (Philip Ball calls it the MWI hypothesis). In this scenario, the universe spits into 2 (or more) so that all possibilities occur in some universe, but you only experience one of them.

There are other interpretations, like David Bohm’s pilot wave and the ‘transaction’ interpretation, which incorporates the time-symmetrical nature of the wave function. But, for the sake of brevity, I’ll discuss Roger Penrose’s, Paul Davies’ and Freeman Dyson’s.

Roger Penrose describes QM in 3 phases: U, R and C (always designated in bold). U is the evolution of the wave function (in Schrodinger’s equation), R is the observation or ‘decoherence’ when the wave function ‘collapses’ (or simply disappears) and C is the classical physics phase. Penrose thinks gravity plays a role in decoherence but I won’t discuss that here. 

Paul Davies argues for John Wheeler’s famous “…participatory universe” in which observers—minds, if you like—are inextricably tied to the concretization of the physical universe emerging from quantum fuzziness over cosmological durations.

This comes from Wheeler’s famous thought experiment that light from a distant quasar could be ‘lensed’ by an intervening massive object, like a galaxy, but we don’t know what path the light takes until it’s observed. This is an extension of his ‘delayed choice’ thought experiment relating to the double slit experiment (later confirmed in a laboratory setting).

Davies discusses this very cogently in an on-line paper and references another paper by Freeman Dyson, where he says, “Dyson concludes that a quantum description cannot be applied to past events.”

Personally, I agree with Dyson that QM describes the future and classical physics describes the past. In other words, I argue that the wave function is in the future, which is why it is never observed. This is consistent with Penrose’s 3 phases, which logically occur in a temporal sequence.

If one takes this approach to Wheeler’s photon from his quasar, it exists in the future of whatever it interacts with, including an observer’s instrument. Let’s assume, hypothetically, that the instrument is the observer’s eye. Because the wave function is time symmetrical the ‘delayed choice’ is really a backwards-in-time pathway to the photon’s source, so the observer sees it instantaneously in the past. In effect, this is the so-called transactional interpretation.

Richard Feynman’s path integral method of QED takes the sum of every path possible (most of which cancel out) to give a probability of where a particle (including a photon) will be observed. If all these paths exist in the future, that’s not a problem; only one of them will exist in the past, observed in retrospect. This is the opposite of the MW interpretation which claims all paths exist simultaneously.

Freeman Dyson comes to the following conclusion: 

“We do not need a human observer to make quantum mechanics work. All we need is a point of reference, to separate past from future, to separate what has happened from what may happen, to separate facts from probabilities.”

The curious thing about that statement is that the ‘point of reference’ is consciousness, because (as Schrodinger pointed out in What is Life?) consciousness is the only thing we know that exists in the continuous present.

This doesn’t make the observer the cause, because the cause is still at the photon’s source. It’s just that consciousness happens to be present in the ‘now’ between the QM future and the classical physics past that Dyson references.

Here is the link to both Davies’ and Dyson’s discussions.

Quantum mechanics, entanglement, gravity and time

I wrote a post on Louisa Gilder’s well researched book, The Age of Entanglement, 10 years ago, when I acquired it (copyright 2008). I started rereading it after someone on Quora, with more knowledge than me, challenged the veracity of Bell’s theorem, also known as Bell’s Inequality, which really changed our perception of quantum phenomena at its foundations. Gilder’s book is really all about Bell’s theorem and its consequences, whilst covering the history of quantum mechanics over most of the 20^th Century, from Bohr through to Feynman and beyond.

Gilder is not a physicist, from what I can tell, yet the book is very well researched with copious notes and references, and she garnered accolades from science publications as well as literary reviewers. Her exposition on Bell’s theorem is technically correct to the best of my knowledge, which she provides very early in the book. 

She goes to some length to explain that the resolution of Bell’s theorem is not the obvious intuitive answer that entangled particles are like a pair of shoes separated in space and time, so that if you find the right-handed shoe you automatically know that the other one must be left-handed. This is what my interlocutor on Quora was effectively claiming. No, according to Gilder, and everything else I’ve read on this subject, Bell’s theorem is akin to finding too many coincidences than one would expect to find by chance. The inequality means that if results are found on one side of the inequality then the intuitive scenario is correct, and if they are on the other side, then the QM world obeys rules not found in classical physics.

The result is called ‘non-local’, which is the opposite of ‘local’, a term with a specific meaning in QM. Local means that objects are only affected by ‘signals’ that travel at the speed of light. Non-local means that objects show a connectivity that is not dependent on lightspeed communication or linkage.

It was Schrodinger who coined the term ‘entanglement’, claiming that it was the defining characteristic of QM.

I would not call that ‘one’ but rather ‘the’ characteristic trait of quantum mechanics. The one that enforces its entire departure from classical lines of thought.

I’ve also recently read an e-book called An Intuitive Approach to Quantum Field Theory by Toni Semantana (only available in e-book, 2019), so it’s very recent. It’s very good in that Semantana obviously knows what he’s talking about, but, even though it has minimum mathematical formulae, it’s not easy to follow. Nevertheless, he covers esoteric topics like the Higgs field, gauge theories, Noether’s theorem (very erudite) and Feynman diagrams. It made me realise how little I know. It’s relevance to this topic is that he doesn’t discuss entanglement at all.

Back to Gilder, and it’s obvious that you can’t discuss entanglement and locality (or non-locality) without talking about time. If I can digress, someone else on Quora provided a link to an essay by J.C.N. Smith called Time – Illusion and Reality. Smith said you won’t find a definition of time that doesn’t include clocks or things that move. In fact, I’ve come across a few people who claim that, without motion, time has no reality. 

However, I have a definition that involves light. Basically, time is the separation between events as measured by light. This stems from the startling yet obvious fact, that if lightspeed was not finite (instantaneous) then everything would happen at once. And, because lightspeed is the same for all observers, it determines the time difference between events, even though the time measured may differ for different observers, as per Einstein’s special theory of relativity. (Spacetime between events for all observers is the same.)

When I was in primary school at the impressionable age of 10 or 11, I was introduced to relativity theory, without being told that is what it was. Nevertheless, it had such an impact on my still-developing brain that I’ve never forgotten it. I can’t remember the context, but the teacher (Mr Hinton) told us that if you travel fast enough clocks will slow down and so will your heart. I distinctly remember trying to mentally grasp the concept and I found that I could if time was a dimension and as you sped up the seconds, or whatever time was measured in, they became more frequent between each heartbeat, so, by comparison, your heart slowed down. One of the other students made the comment that ‘if a plane could fly fast enough it would come back to land before it took off’. I’m unsure if that was a product of his imagination or if he’d come across it somewhere else, which was the impression he gave at the time. Then, thinking aloud, I said, It’s impossible to go faster than time, as if time and speed were interdependent. And someone near me turned, in a light-bulb moment, and said, You’re right.

My attempt at conceptually grasping the concept was flawed but my comment was prescient. You can’t travel faster than time because you can’t travel faster than light. For a photon of light, time is zero. The link between time and light is an intrinsic feature of the Universe, and was a major revelation of Einstein’s theory of relativity.

J.C.N. Smith argues in his essay that we have the wrong definition of time by referring to local events like the rotation of the planet or its orbit about the sun, or, even more locally, the motions of a pendulum or an atomic clock. He argues that the definition of time should be the configuration of the entire universe, because at any point in time it has a unique configuration, and, even though we can’t observe it completely, it must exist. 

There is a serious problem with this because every observer of that configuration would see something completely different, even without relativistic effects. If you take the Magellanic Clouds, which you can see in the southern hemisphere with the naked eye on a cloudless, moonless night, you are looking 150,000 to 190,000 years into the past (there are 2 of them), which is roughly when homo sapiens emerged from Africa. So an observer on a world in the Magellanic Clouds, looking at the Milky Way galaxy, would see us 150,000 to 190,000 years in the past. In other words, no observer in the Universe could possibly see the same thing at the same time if they are far enough apart.

However, Smith is right in the sense that the age of the Universe infers that there is a universal ‘now’, which is the edge of the Big Bang (because it’s still in progress). The Cosmic Microwave Background Radiation is the earliest light we can see (from 380,000 years after the Big Bang) yet our observation of it is part of our ‘now’.

This has implications for entanglement if it’s non-local. If Freeman Dyson is correct that QM describes the future and classical physics describes the past, then the collapse or decoherence of the wave function represents ‘now’. So ‘now’ for an observer is when a photon hits your retina and you immediately see into the past, whether the photon is part of a reflection in a mirror or it comes from the Cosmic Background Radiation. It’s also the point when an entangled quantum particle (which could be a photon or something else) ‘fixes’ the outcome of its entangled partner wherever in the Universe it may be.

If entangled particles are in the future until one of them is observed then they infer a universal now. Or does it mean that it creates a link back in time across the Universe? 

John Wheeler believed that there was a possibility of a connection between an observer and the distant past across the Universe, but he wasn’t thinking of entanglement. He proposed a thought experiment involving the famous double-slit experiment, whereby one makes an observation after the particle (electron or photon) has passed through the slit but before it hits the target (where we observe the outcome). He predicted that this would change the pattern from a wave going through both slits to a particle going through one. He was later vindicated (after his death). Wheeler argued that this would imply that there is a ‘backwards-in-time’ signal or acausal connection to the source. He argued that this could equally apply to photons from a distant quasar, gravitationally lensed by an intervening galaxy.

Wheeler’s thought experiment makes sense if the wave function of the particle exists in the future until it is detected, meaning before it interacts with a classical physics object. Entanglement also becomes ‘known’ after one of the entangled particles interacts with a classical physics object. Signals into the so-called past are not so mysterious if everything is happening in the future of the ‘observer’. Even microwaves from the Cosmic Background Radiation exist in our future until we ‘detect’ them.

Einstein’s special theory of relativity tells us that simultaneity can’t be determined, which seems to contradict the non-locality of entanglement according to Bell’s theorem. According to Einstein, ‘now’ is subjective, dependent on the observer’s frame of reference. This implies that someone’s future could be another person’s past, but this has implications for causality. No matter where an observer is in the Universe, everywhere they look is in their past. Now, as I explained earlier, their past maybe different to your past but, because all observations are dependent on electromagnetic radiation, everything they ‘see’ has already happened.

The exception is the event horizon of a black hole. According to Viktor T Toth (a regular contributor to Quora), the event horizon is always in your future. This creates a paradox, because it is believed you could cross an event horizon without knowing it. On the other hand, an external observer would see you frozen in time. Kip Thorne argues there is no matter in a black hole, only warped spacetime. Most significantly, once you pass the event horizon, space effectively becomes uni-directional like time – you can’t go backwards the way you came.

As Toth has pointed out a number of times, Einstein’s theory of gravity (the general theory of relativity) is mathematically a geometrical theory. Toth also points out that We can do quantum field theory just fine on the curved spacetime background of general relativity. Another contributor, Terry Bollinger, explains why general relativity is not quantum:

GR is a purely geometric theory, which in turn means that the gravity force that it describes is also specified purely in terms of geometry. There are no particles in gravity itself, and in fact nothing even slightly quantum.

In effect, Bollinger argues that quantum phenomena ‘sit’ on top of general relativity. I contend that gravity ultimately determines the rate of time, and QM uses a ‘clock’ that exists outside of Hilbert space where QM ‘sits’ (according to Roger Penrose, as well as Anil Ananthaswamy, who writes for New Scientist). 

So what happens inside a black hole, which requires a theory of quantum gravity? As Freeman Dyson observed, no one can get inside a black hole to report or perform an experiment. But, if it’s always in one’s future, then maybe quantum gravity has no time. John Wheeler and Bryce de-Witt famously attempted to formulate Einstein’s theory of general relativity (gravity) in the same form as electromagnetism, and time (denoted as t) simply disappeared. And as Paul Davies pointed out in The Goldilocks Enigma, in quantum cosmology (as per the Wheeler de-Witt equation), time vanishes. But, if quantum cosmology is attempting to describe the future, then maybe one should expect time to disappear.

Another thought experiment: if you take an entangled particle to the other side of the visible universe (which would take something like the age of the Universe) and then they instantly ‘link’ or ‘connect’ non-locally, it still requires less than lightspeed to separate them. So you won’t achieve instantaneous transmission, even in principle, because you have to wait until its entangled ‘partner’ arrives at its destination. Or, as explained in the video below, the 'correlation' can only be checked in classical physics.

Addendum: This is the best explanation of QM entanglement and Bell's Theorem (for laypeople) that I've seen:

The Lagrangian – possibly the most fundamental mathematical principle in physics

This is something I wrote on Quora, which was ‘upvoted’ by a physics tutor (Mike Milner) and someone with an MSc (Dimitrios Kalemis), which gives it some credence.

I’ve written about all of this before in previous posts, but probably not as succinctly, which hopefully makes it easier to follow.


How does an electron know beforehand that it's a single slit or double slit so it decides whether to create an interference pattern or not?

Obviously it doesn’t. It’s like asking how does a ball thrown in the air know what path to follow? These 2 questions have more in common than you might think.

There is a fundamental principle in physics called the principle of least action, and Richard Feynman used it to describe the trajectory of a ball in a gravitational field and also as the basis for his path integral method of quantum mechanics (QM).

The principle of least action is that the difference between the potential energy and the kinetic energy of a particle will always be a minimum and, mathematically, this is called a Lagrangian. In his book, Six Not-So-Easy Pieces, Feynman demonstrates how this applies to a body in a gravitational field when it follows the path dictated by a geodesic, which, in Einstein’s theory of relativity, is the path of maximum relativistic time. It turns out that this is the shortest path and also the path of least action, as determined by the Lagrangian.

Feynman gives the following analogy. Imagine a lifesaver needing to run along a beach and then swim out to rescue a bather in distress in the surf. The lifesaver could run along the beach (at a diagonal) until he (or she) is perpendicular to the swimmer in the waves and swim out. Or the lifesaver could run straight into the surf and swim diagonally to the swimmer. But the optimum path is something in between these 2 and that’s the path of least action or least time. It’s also the path of light when it refracts through glass or any other medium.

It was Paul Dirac who originally wrote a Lagrangian for QM and Feynman used his result to derive Schrodinger’s equation. Feynman’s approach to the 2 slit problem or any other QM problem was to combine all the possible paths the electron (or a photon) could take. By ‘combine’ this means adding all the phases of the wave function, most of which cancel each other out. Then, using Born’s rule, he derived the probabilities of where the electron would hit the screen on the other side of the slit(s).

In his book, QED, he provides a graphic demonstration using this method to derive the path of a photon hitting a mirror. He says ‘the light goes where the time is least.’

In response to your specific question, the electron’s path is only determined retrospectively after it hits the screen on the other side of the slit(s). Freeman Dyson (who collaborated with Feynman) argues that QM cannot describe the past but only the future. So prior to the electron hitting the screen, QM describes the probabilities of where it will go, which is mathematically dependent on it being able to go everywhere at once. If there are 2 slits then this means it can go through both and if there is only one slit then it can only go through one. So the observation made retrospectively confirms this.

Addendum: Sabine Hossenfelder gives a much more erudite exposition in this video. And I agree with her - it's the closest we have to a 'theory of everything'.

Quantum mechanics and the arrow of time

Before I get started I need to make an important point. Every now and then I hear or read about someone who puts my life into perspective. Recently, I read an article on Lisa Harvey-Smith, a 39 year old, educated in England who is ‘Group Leader’ of astronomy at Australia’s CSIRO. She appeared on an ABC programme called Stargazing Live (last year) with Brian Cox and Julia Zemiro. She won the 2016 Eureka Science Prize for ‘promoting science research in Australia’. She also runs ultra-marathons (up to 24hs) and is an activist for LGBTI people. The point I’m making is that she’s a real scientist, and by comparison, I’m a pretender.

And I make this point because many people who know more about this subject than me will tell you that much of what I have to say is wrong. So why should you even listen to me? Because I have a philosophical point of view on a subject with many philosophical points of view, some of which border on science fiction. For example: interacting parallel universes; and physical reality only becoming manifest when perceived by a conscious observer. I’ve written about both of these philosophical perspectives on other posts, but they indicate how much we don’t know and how difficult it is to reconcile quantum mechanics (QM) with what we actually perceive in our everyday interaction with the world.

I recently read a very good book on this subject by Philip Ball titled Beyond Weird. He gives a history lesson whilst simultaneously discussing the philosophical nuances inherent in QM in the context of experimental evidence. Ball, more than any other author I’ve read in recent times, challenges my perspective, which makes him all the worth while to read. But in so doing, I’m able to delineate with more confidence between the lesser and greater contentious aspects of my viewpoint. In fact, there is one point which I now realise is the most contentious of all, and it is related to time.

Regarding the title of this post, they seem like separate topics, but I’m aware others have made this connection; in particular Richard A Muller in NOW; The Physics of Time, though he didn’t really elaborate. He did, however, elaborate on why entropy does not provide the arrow of time, which is an oft made misconception. And it is one I’ve made myself in the past, but I now fully believe that the cause and effect is the other way round. Entropy increases with time due to probabilities. There is a much higher probability for disorder than order providing the system is in equilibrium. If there is an energy source (like the sun) that keeps a system out of equilibrium then you can have self-organising complexity occurring (such as life).

I’m unsure if QM provides an ‘arrow of time’, as people like to express it, but I do believe it provides an asymmetry, which is best expounded by Roger Penrose’s 3 phases of U, R and C. U is the evolution of the wave function as expressed by Schrodinger’s equation, R is the measurement or observation process (also called decoherence of the wave function) and C is the classical physics world which we generally call reality. These always occur in that sequence, hence the logical temporal connection.

I say ‘always’ yet Ball gives an example whereby physicists in Canada in 2015 ‘reversed the entanglement of photons’ in a crystal, which Ball calls 'recoherence'. But he also describes it as ‘.. the kind of exception that, in the proper sense, proves the rule.’ The ‘rule’, according to Ball, is that decoherence is the loss of quantum information to the environment. This is a specific interpretation by Ball, which has merit and is analogous to entropy (though he doesn’t make that connection) therefore time-directional in the same way that entropy is.

Towards the end of his book, Ball effectively argues that an ‘information’ approach to QM is the most logical approach to take and talks about a ‘reconstruction’ of QM based on principles like the ‘no cloning’ rule (quantum particles can’t be copied so teleportation destroys the original), the 'no-signalling' rule (you can’t transmit information faster than light) and there is ‘no unconditional secure bit commitment’ (which limits quantum encryption). These 3 were called ‘no-go principles’ by Rob Clifton, Jeffrey Bub and Hans Halvorson. To quote Bub from the University of Maryland: ‘[QM] is fundamentally about the representation and manipulation of information, not a theory about the mechanics of nonclassical waves or particles’. In other words, we scrap wave functions and start again with information. Basically, Ball is arguing that QM should be based on a set of principles and not mathematical formulations, especially ones that describe things we can't perceive directly (we only see interference patterns, not waves per se).

Of course, we’ve known right from its original formulation, that we don’t need Schrodinger’s equation or his wave function to perform calculations in QM (I’ll talk about QED later). Heisenberg’s matrices preceded Schrodinger’s equation and gave the same results without a wave function in sight. So how can they be reconciled philosophically, if they are mathematically equivalent but conceptually at odds?

From my limited perspective, it seems to me that Heisenberg’s and Schrodinger’s respective mathematical approaches reflect their philosophical approaches. In fact, I would argue that they approached the subject from 2 different sides, even opposite sides, and came up with the same answer, which, if I’m correct, says a lot.

Basically, Schrodinger approached it from the quantum side or U phase (to use Penrose’s nomenclature) and Heisenberg approached it from the measurement side or R phase. I’m reading another book on the same subject, What is Real? by Adam Becker, which I acquired at the same time as Ball’s book, and they are complementary, in that Becker’s approach is more historical yet also examines the philosophical aspects. Heisenberg was disappointed (pissed off may be more accurate) at Schrodinger’s success, even though Heisenberg’s matrix approach preceded Schrodinger’s wave function.

But it was Heisenberg’s specific interest in the ‘measurement problem' that led him to his famous Uncertainty Principle and a Nobel Prize. Schrodinger’s wave function, using a Fourier transform, also gives the Uncertainty Principle, so mathematically they are still equivalent in their outcomes. But the point is that Schrodinger’s wave function effectively disappears as soon as a measurement is made, and Heisenberg’s matrices with their eigenvalues don’t tell us anything about the evolution of any wave function because they don’t express it mathematically.

Ball makes the point that Schrodinger’s and Heisenberg’s approaches reflect an ontological and epistemological consideration respectively, which he delineates using the shorthand, ‘ontic’ and ‘epistemic’. In this sense, the wave function is an ontic theory (this is what exists) and Heisenberg and Bohr’s interpretation is purely epistemic (this is what we know).

I’m getting off the track but it’s all relevant. About a month ago, I wrote a letter to New Scientist on 'time'. This is an extract:

There is an obvious difference between time in physics - be it governed by relativity, entropy or quantum mechanics - and time experienced psychologically by us. Erwin Schrodinger in his seminal tome, What is Life? made the observation that consciousness exists in a constant present, and I would contend that it's the only thing that does; everything else we perceive has already happened, except quantum mechanics, which prior to a 'measurement' or 'observation', exists in the future as probabilities. An idea alluded to by Sir William Lawrence Bragg, albeit using different imagery: the future are waves and the past are particles – "The advancing sieve of time coagulates waves into particles at the moment ‘now’". So it's not surprising that the concepts of past, present and future are only meaningful to something with consciousness, because only the continuous ‘now’ of consciousness provides a reference.

Those of you who regularly read my blog will notice that this is consistent with a post I wrote earlier.

The letter was never published and New Scientist inform you in advance that they refer letters to ‘experts’ and that they don’t provide explanations if they don’t publish, which is all very fair and reasonable. I expect in this case the expert (possibly Philip Ball, as I referenced his review of Carlo Rovelli’s book) probably said that this is so wrong-headed that it shouldn’t be published. On the other hand, their expert (whoever it was) may have said this insight is so obvious it’s not worth mentioning (but I doubt it).

I expect that both my citing of Erwin Schrodinger and of Sir William Lawrence Bragg would have been considered, if not contentious, then out of date, and that my views are far too simplistic.

So let me address these issues individually. One reads a lot of words (both in science and philosophical essays) on the so-called ‘flow of time’, and whether it’s an illusion or whether it’s only in the mind or whether it’s the wrong metaphor altogether; as if time is a river and we stand in it and watch it go by.

But staying with that metaphor, the place where we are standing remains ‘now’ for ever and always, whilst we watch the future become the past in a series of endless instants. In fact, we never see the future at all, which is why I say that ‘everything we perceive has already happened’. But the idea that this constant now that we all experience is a consequence of consciousness is contentious in itself. We don’t see ourselves as privileged in that sense; we assume that it only seems a privileged position because we witness it. We assume that everything in the Universe rides this wave of now. But, for everything else, the now becomes frozen, especially if ‘now’ represents the decoherence of a quantum wave function into a classical particle. Without consciousness, ‘now’ becomes relative, an objective point in time between a future event and a past event that quickly only becomes perceived as a past event.

Let’s look at light, because it’s the most ubiquitous quantum phenomena that we all witness all the time (when we are awake). The other thing about light is that we can examine it on a cosmic scale. The Magellanic Clouds (galaxies) are approximately 200,000 light years from here and we can see them with the naked eye in Australia, if you can get away from townships on a clear night. So we can literally look 200,000 years into the past. (That is roughly when homo sapiens evolved in Africa, according to one reference I looked up.)

Now, in my previous post I argued that light is effectively in the future until it interacts with matter, so how is that possible if it took the entire history of humanity to arrive at my retina? Well, from the star’s perspective (in the Magellanic Cloud) it’s in the future because it’s going away from it into the future, quite literally. And no one can perceive the light ray until it interacts with something, so it’s always in the future of whatever it interacts with. For the photon itself, it travels in zero time. Light turns time into distance, which is why there is really only spacetime, and if light didn’t do that (because it has a constant velocity) then everything would happen at once. So, as soon as it hits my retina and not before, I can see 200,000 years into the past. That's a quantum event.

Early in his book, Adam Becker (What is Real?) provides a very good metaphor. A traveller arrives at a fork in a path and we don’t know which one he takes until he arrives at his destination. According to QM he took both at once until someone actually meets him and then we learn he only took one. The 2 paths he can take are in the future and the one he actually took is in the past. But wait, you say: in QM a photon or particle can literally take 2 paths at once and create an interference pattern. Actually, the interference pattern is created by the probabilistic outcomes of individual photons or particles, so there is still only one path for each one.

Superposition is a much misunderstood concept. As Ball explains in a foonote: “…superposition is not really ‘two states at once’, but a circumstance in which either state is a possible measurement outcome.”

He gives a very good description of the Schrodinger wave function and its role in QM:

The Schrodinger equation defines and embraces all possible observable states of a quantum system. Before the wave function collapses (whatever that means) there is no reason to attribute any greater degree of reality to any of these possible states than to any other. For remember that quantum mechanics does not imply that the quantum system is actually in one or other of these states but we don’t know which. We can confidently say that it is not in any one of these states, but is properly described by the wavefunction itself, which in some sense ‘permits’ them all as observational outcomes. Where then do they all go, bar one, when the wavefunction collapses? (emphasis in the original)

He was making this point in the context of explaining why the parallel universe or ‘Many World Interpretation’ (which he calls MWI) is so popular and seductive, because in the MWI they do all exist. Ball, by the way, is not a fan of MWI and gives extensive and persuasive arguments against it.

This leads logically to Feynman’s integral path method or his version of QED (quantum electrodynamics) where all paths are allowed, but the phase interaction of the superposed wave functions cancel most of them out. Only a wave function version of QM with its time dependent phases can provide this interaction. Brian Cox gives a very good, succinct exposition of Feynman’s version of QM on Youtube and Freeman Dyson, who worked with Feynman and who originally showed that the independent work of Schwinger, Feynman and Tomonaga were equivalent, which got them all the Nobel Prize (except Dyson), explains that Feynman’s integral method predicts 'future probabilities from a sum over histories'. The point is, as Ball says himself, none of these histories actually happen. I argue that they never happen because they’re all in the future. Certainly, we never see them or measure them, but one of the probability outcomes will be realised when it becomes the past.

Because a specific path is only known once an observation is made, it appears that we are determining the path backwards-in-time, which has been demonstrated experimentally. I feel this is the key to the whole enigma, like the photon coming from the Magellanic Clouds – the path is revealed in retrospect. Until it’s revealed, it’s effectively in our future. Also this is consistent with the asymmetry in time we all experience. The future is many paths (as per QED) but the past is only one.

Ball argues consistently that there is a transition from ‘quantumness’ to classical physics (as per Penrose, though he doesn’t reference Penrose) but he argues that classical physics is a special case of QM (which is the orthodoxy).

His best argument is that decoherence is the loss of quantum information to the environment, which can happen over time, so not necessarily in an instance. He uses the same idea to explain why large objects decohere virtually instantaneously, because they are exposed to such a massive expanse of the environment.

There is much about QM I don’t discuss, like spin states that distinguish bosons from fermions and the role of symmetry and Emmy Noether’s famous theorem that relates symmetry to conservation laws (not only in QM but relativity theory).

I’m trying to understand QM and how it relates to time. Why is it, as Ball himself asks, are there many possibilities that become one? My contention is that this is exactly what distinguishes the future from the past as we experience it. The enigma with QM, as when we look backwards in time through the entire cosmos, is that those many paths only become one when the quantum object (photon or particle) interacts with something, forcing a wave function collapse or decoherence. Is there a backwards-in-time cosmic scale loop as proposed by John Wheeler? Maybe there is. Maybe the arrow of time goes both ways.


Footnote: This video gives a good summary of QM as discussed above; in particular, the presenter discusses the fundamental enigma of the many possibilities becoming one, and the many paths becoming one, only when an observation or measurement is made. He specifically discusses the so-called Copenhagen interpretation, but in effect describes QED.

Addendum 1: Sometimes I can't stop thinking about what I've written. I'm aware that there is a paradox with a light ray from the past intersecting with our future, so I've shown it in a very crude spacetime diagram, with time on the vertical axis and space on the horizontal axis. The Magellanic Clouds and Earth are 200,000 light years apart and there is a light cone which goes at 45 degrees from the source to the Earth 200,000 years into the future. (Actually, the small Magellanic Cloud is 199,000 while the large one is 158,000, which is probably the one you can see with the naked eye, so maybe you need a telescope for this after all.)

It's assuming that the distance between the Magellanic Clouds and Earth doesn't change (for simplicity) which is almost certainly not true. It allows the Earth to be a vertical line on the spacetime diagram with light being at 45 degrees, so they intersect 200,000 light years in the future.

It also suggests that the photon exists in a constant 'now' (until it interacts with something). As I said before, light is unique in that it has zero time, which explains that particular effect. Consciousness is unique in that it provides a reference for ‘now’ all the time. Light is always in the future of whatever it interacts with, when it becomes ‘now’, then becomes frozen in the past, possibly as an image (e.g. a photo) or a dot on a screen. Consciousness never becomes frozen, but it does become blank sometimes.

Addendum 2: This is a Youtube lecture by Carlo Rovelli, who would tell you that virtually everything I've said above is wrong, including what I said about entropy and time.

Addendum 3 (Conclusion): I've since read Carlo Rovelli's latest book, The Order of Time, where he completely dismantles our intuitive concept of time. For one, he says that Einstein has demonstrated that time doesn't flow at the same rate everywhere, but then effectively says that time doesn't flow at all. He points out that in QM, time can flow both ways mathematically, which is the U phase (using Penrose's nomenclature), and that the only time direction comes from entropy, which is contentious, in as much as many physicists believe that entropy is not the cause of time's apparent direction, but a consequence.

He says that there is no objective 'now', yet elsewhere I've read him being quoted as saying 'now' is the edge of the big bang. In his book, he doesn't discuss the age of the Universe at all, yet it has obvious ramifications to this topic.

There are 4 ways of looking at QM (5 if you include multiple worlds, which I'm not). There is the Copenhagen interpretation, which effectively says the only reality is what we measure or observe, and the wave function is simply a mathematical device for making probabilistic predictions prior to that.

There is Bohm's pilot wave theory, which says there was always a path, created by the pilot wave but not known until after our observation.

There is QED, in particular Feynman's sum over integral interpretation, that says there are an infinitude of paths, most of which cancel each other out, that give the most probabilistic outcome. When the outcome is known they all become irrelevant.

There is a so-called transactional interpretation that says the wave function goes both forwards and backwards in time, formulated by John Cramer in the mid 1980s, but foreshadowed by Schrodinger himself in 1941 (John Gribbin. Erwin Schrodinger and the Quantum Revolution, pp.161-4).

My interpretation effectively captures all of these (except multiple worlds). I don't think there is a pilot wave but I think there is 'one path' that is discovered after the observation. If you take the example I use in the main text; of observing the light from a star in the Magellanic Cloud: when you see it, you instantly look 200,000 light years into the past (or thereabouts). So there is a link between your current 'now' and a 'now' 200,000 years ago. My contention is that this is only possible because there is a backwards in time path from your eyeball to the star.

Addendum 4: Much of what I discuss above was foreshadowed in a post I wrote over 2 years ago; possibly more succinct and more accessible.

Addendum 5: This is a brief interview with Freeman Dyson, which has some relevance to this post. I have to say that Dyson probably comes closest to expressing my own views on QM and classical physics - that they are, in essence, incompatible. By his own admission, these views are not shared by most other physicists (if at all).