Space and time: still a mystery after all this (time?)

How’s that for a self-referential title, hence the question mark and parentheses. It highlights the fact that time is an everyday phenomenon that literally runs our lives and yet it remains one of the great mysteries of the Universe, still debated among philosophers and scientists. You may think that space is less of a mystery, yet it sparks debate as well, even without Einstein’s revelation that they are cosmologically entwined thanks to the constant speed of light, c.

The problem is with how do we categorise space and time. Are they entities, parameters, dimensions, metrics, mathematical constructions? Perhaps all of the above. I think we can safely say they are not physical objects, yet they determine the relationships between objects everywhere in the Universe, including those that we can’t perceive. In fact, some scientists would argue that time and space are all about relationships and nothing else, which I’ll return to later.

 

But let’s start with one obvious question, which was raised by Kant and still persists today, thanks to Donald Hoffman (refer my last post), and that is: are time and space simply constructs of the mind? To quote Kant from Critique of Pure Reason:

 

But this space and this time, and with them all appearances, are not in themselves things; they are nothing but representations and cannot exist outside our minds.

 

The problem with this viewpoint is that it’s readily believed by almost everyone that space and time existed for billions of years before any ‘mind’ arose in the Universe.

 

Another contentious point is to whether space is an ‘entity’ that ‘expands’ and ‘stretches’ as the Universes itself expands (which is not disputed). Viktor T Toth, a renowned expert on physics on Quora, argues very strongly that it doesn’t and what we witness is the ‘distance’ actually increasing between objects. Proponents against space expanding (like Toth) argue that the space within atoms doesn’t expand. My response is that the size of atoms is determined almost solely by Planck’s constant (h), for which there is no evidence that it changes with the universe’s expansion.

 

However, space can travel faster than light, which suggests it is an entity. This is not disputable, and it’s why there is a horizon to the observable universe (refer my post on the End of the Universe). It’s also why we can incorporate ‘inflation’ into the birth of the Universe. It also has ramifications for black holes, which I’ll come to later. According to Einstein’s theories of relativity, both space and time can change according to the observer and these changes are measurable. In other words, space and time are not ‘fixed’ and they are affected by gravity. In fact, Einstein’s famous formula for his general theory has the curvature of spacetime on one side and the momentum-energy tensor on the other side. In other words, spacetime is curved by energy/matter. To quote John Wheeler: “Spacetime tells matter how to move; matter tells spacetime how to curve.”

 

During this discussion, I’ll cite people who know a lot more than me, like Viktor T Toth and John Wheeler (already cited), even if I disagree with them. But I’m going to attempt the impossible: I’m going to argue ideas that I consider obvious, though not incontrovertible, and I will probably fail, since they will include black holes, quantum mechanics and relativity, all of which I don’t have as much knowledge as I would like. But bear with me, because it’s mostly just logic.

 

I want to point out, right at the start, that I’m not one of those people who think Einstein got it wrong, quite the contrary, but I will point out the limitations of his theory based on what we can actually observe. And that’s a good place to start. A common diagram used to visualise Einstein’s formulation of spacetime is the light cone going both forwards and backwards in time. If you are an observer at the centre of this cone you can only be affected by events from the past within the past light cone, and you can only affect events in the future within the future light cone. Everything else outside these cones can’t be observed or have a causal relationship with you, and this is what I mean when I say relativity has limitations because they are real limitations. Sometimes people will tilt the cones over, indicating movement on your part and the horizontal plane, called the 'hypersurface present', also tilts over. However, there is no causal connection along that 'hypersurface' (through spacetime), according to what I’ve just described.

But this brings one to the subject of simultaneity, because Einstein showed with his famous train and platform thought experiment that 2 observers in different frames of reference could observe different sequences of the same event or perceive a difference in what occurs simultaneously.

 

This is a video that explains this better than I can, including the mathematics involved. Two things worth mentioning: the lecturer includes the spatial Lorenz contraction as well as the time dilation in his calculations; and the observer in the same frame of reference as the source of light sees zero difference and therefore observes a ‘true simultaneity’, though no one calls it that. I’ve long argued that the ‘other observer’ who doesn’t see the simultaneity, observes a difference in the Doppler effect caused by the ‘moving’ frame of reference with the moving light source, which should tell that observer that their observation is incorrect. The Doppler effect tells the observer if the light source is in their frame of reference or a frame of reference moving relative to them. It’s the Doppler effect that tells us that the Universe is expanding uniformly in all directions – it has no centre. It also tells us that we’re moving relative to the CMBR (cosmic microwave background radiation). In other words, we can measure our ‘velocity’ relative to the whole of spacetime, which, of course, is the Universe.

 

I’ve explained elsewhere how different observers in different parts of the Universe literally see different ‘now(s)’. They can literally see events occurring in opposite sequences, as a consequence of the finite speed of light, even without relativistic effects. However, if the events have a causal relationship, then all observers will see them in the same sequence. But this also means that my present will be seen in another observer’s past in their future, but it doesn’t mean the converse: that their future can be seen in my present. In fact, the relationship is reciprocal because I will see their past in my present. Observers can only see another observer’s past, no matter where they are. No observer can see another observer’s future. 

 

To give an example, a hypothetical observer in the Small Magellanic Cloud would see us 210,000 years ago when we were just emerging from Africa. Likewise, we would observe them 210,000 years ago (relative to us) if that was physically possible. Therefore, I don’t hold to the widely held view that we can theoretically see another observer’s future (due to the tilting 'hypersurface' plane in the light cone graphic), which infers that the future must already exist for everyone.

 

We know from the twin paradox thought experiment, as well as data from orbiting satellites, that clocks do literally run at different rates due to gravity as well as motion (your satnav depends on making corrections). Also, the famous muon observations arriving on the Earth’s surface. So both special and general theories of relativity change the rate of time, yet when the clocks are back in the same reference frame, they will show a different time duration while agreeing on where they are in the spacetime co-ordinates of the solar system. In other words, they don’t exist in different ‘now(s)’ just because they measured different durations to arrive at the same destination.

 

We know that different animals see time ‘flow’ at different rates. Many birds and insects see the world in slow-motion compared to us. This means they will see the hands of a clock literally moving slower while telling the same time. As Paul Davies has pointed out, if time was to slow down or speed up, you wouldn’t notice. But you can notice if you compare clocks in relativity. My point is that ‘now’ doesn’t change for these creatures even though they perceive time flowing at a different rate to us.

 

Well, I contend the same is true on a cosmic scale. If you were to go near the event horizon of a black hole, like in the movie, Interstellar, time would slow down for you compared to everyone back on Earth, even though you wouldn’t notice it. My argument is that this is no different, perceptually, to the bird observing time going slower. If you were to use the Doppler effect of receding galaxies as a clock, they would actually appear to be going faster (assuming you could take accurate enough measurements) compared to what Earthlings observed, and when you returned, you would agree on what ‘now’ is, compared to these distant cosmic clocks, though you would be considerably younger than your counterparts, if they were still alive, but more likely you would be meeting their subsequent generations.

 

And this is true even on Earth, where clocks run infinitesimally faster on mountaintops compared to sea level. But you don’t see an accumulated difference in ‘now’ over millions of years of the Earth’s rotation. All the while, the clocks are in the same ‘present’ while they are measuring different rates of time passing.

 

Carlo Rovelli gave a talk at the Royal Institute on ‘time’, where he argues that there is no ‘universal time’. But during the 15min question time (shown in another video), he contends that we arrive at a cosmic time for the Universe by taking an ‘average’. Brian Greene, in his book, The Fabric of the Universe, said something similar. However, if you lived on a planet orbiting near a black hole, surely the age of the Universe would be much less than what we observe, because any clock would be measuring time passing at a much slower rate than what we measure on Earth. Like the clocks on top of the mountains on Earth, I don’t believe hypothetical observers orbiting close to a black hole, perceive a ‘now’ that progressively gets out of step with the ‘now’ Earthlings observe over the course of their lives in the Universe, even if they measured a different age. In other words, I contend that you can have a universal now for the whole universe even if different clocks measure different rates of time dependent on where they are located.

 

Another video, which is an interview with loop quantum gravity theorist, Lee Smolin, describes time and space as being separate, which is both heretical and interesting. I think he has a point when you consider that, on a cosmic scale, time is finite and space is possibly infinite. Space could also be finite but perceptually infinite, like a hyperbolic universe, but, as Marcus du Sautoy pointed out in his book, What We Cannot Know, if the Universe is truly spatially infinite, we might never know. Smolin conjectures that space could be a consequence of ‘causal relationships’ between physical objects, which he doesn’t elaborate on, but which I find difficult to conceptualise. Causation is determined by the speed of light, otherwise everything would happen at once (Caspar Henderson, A New Map of Wonders). Smolin also contends that time might be an ‘emergent’ property (also without elaborating). The point is that causality requires time axiomatically. The thing about both space and time is that they are dimensions and if you add light (c) into the mix, you get a 4-dimensional universe that is fundamental for it to function in the way it does. With more than 3 spatial dimensions, planets would not have stable orbits, and if there was more than 1 dimension of time you would get time loops. If you have 2 spatial dimensions you would literally fall apart. Also, more than 3 spatial dimensions causes light waves to travel inconsistently. Our universe has the ideal time-space dimensional combination for its goldilocks existence.

 

In the same video, Smolin explains how the event horizon of a black hole breaks causality. This can be seen mathematically by Schwarzchild’s equation for a static black hole, which is described in this video. As the presenter explains, the +ve and -ve signs of the equation change when you cross the event horizon, which breaks causality. Causality is caused by the space dimension being less than the (negative) time dimension, and they are reversed on the other side of the event horizon (watch the video). It should be pointed out that Einstein was initially sceptical about the existence of black holes, even though Schwarzchild derived his equation from Einstein’s tensor.

 

There is a paradox inherent in a black hole (more than one, actually) but the most fundamental one is that time theoretically stops at the event horizon because time is related to light, and light can’t escape a black hole by definition. Viktor T Toth says that ‘the event horizon is always in an observer’s future’, so how can anyone (or anything) fall into a black hole? In a previous post, I speculated that maybe ‘space’ itself ‘falls’ into the black hole and that’s exactly what the guy in the video says. This is only possible because space can travel faster than light, as I described earlier.

 

This is already a lengthy post but I can’t talk about time without mentioning quantum mechanics. The same guy (who talks about black holes), gives a very good summary explanation of Richard Feynman’s path integral formulation of QED (quantum electrodynamics) in this video. It should be pointed out that Julian Schwinger’s ‘field’ interpretation called QFT (quantum field theory) is now more popular, if that’s the right word. In QFT, particles are seen as ‘excitations’ of a quantum field which is everywhere in the Universe. Someone on Quora even suggested that the word ‘particle’ should be erased from every physics text book, because they just don’t exist. Curiously, Feynman, in his book, QED, argued that everything is ‘particles’, but that was in the context of whether quantum phenomena are ‘waves’ or ‘particles’ in the Bohr tradition. I like Freeman Dyson’s view that it depends on whether an event is in an observer’s future or past, but I’m getting ahead of myself.

 

A good place to start with QM is Schrodinger’s equation. Carlo Rovelli, whom I cited earlier, in one of his books, is almost dismissive of Schrodinger’s equation and argues that the wave function (ψ) has misled us in our understanding of QM. But Schrodinger’s wave function is the basis of Feynman’s QED, so that’s where I’ll start.

 

Schrodinger’s equation encapsulates all the characteristics of QM which make it weird: superposition, entanglement and the uncertainty principle. The wave function also incorporates time-reversal symmetry, which is an inherent feature of QM. It doesn’t incorporate relativity, but I’ll come to that later.

 

The thing about Schrodinger’s equation, which is rarely mentioned, is that it describes the future – it makes predictions about where something will be in time. It was Dirac who derived the Lagrangian for QM, and Feynman adopted that for his ‘sum over histories’ or ‘path integral’ formulation, because it calculates the path of ‘least action’, which dictates what something does. (This also applies in a gravitational field, by the way, but I don’t want to confuse you.) Feynman used the proper time (τ) in place of t (that Schrodinger used) which automatically allows for special relativity (as explained in the video).

 

As someone on Quora once explained (David Moore, who is a Sydney based GP), a probability of ONE exists in the past, after the event. In the future, the probability is always less than one. This is what happens when the wave function ‘collapses’, for want of a better word, and neatly incorporates Freeman Dyson’s view that QM describes the future while classical physics describes the past. Feynman’s formulation has an infinity of possible future paths, that he integrates (hence the ‘integral’ in path integral) and also gives the path of least action. There is an element of teleology in this, but I don’t believe it makes the universe deterministic, though others disagree. On a large enough scale, as Schrodinger himself pointed out, you get a statistical deterministic effect, which he coined ‘statistico-deterministic’. But it can’t predict individual events, like when a radioactive isotope will decay, which is the crucial component in his eponymous cat thought experiment.

 

In regard to photons being the ‘particle’ nature of light, Mark John Fernee (physicist at Queensland University and regular Quora contributor) made the point in one of his posts, that if we didn’t observe light as photons, we would not be able to see many of the distant stars that we do. If light was purely a wave, then it would be so dispersed over the massive sphere of its influence it would be too faint to see. But, as a photon, it can arrive in just one point in space, where we happen to observe it.

 

I will leave the last word to Paul Davies. Even though he’s talking about QM in reference to black holes and Hawking radiation, the principle he describes is universal.

 

The very act of measurement breaks the time symmetry of quantum mechanics in a process sometimes described as the collapse of the wave function... the rewind button is destroyed as soon as that measurement is made.

Addendum: This video gives a more detailed and accurate explanation of black holes. It's more complex than my exposition would suggest.

To the End of the Universe

I like to remind myself and others how little I know. It’s one of the reasons I like Quora, where I get to occasionally interact with people who know considerably more than me. One such person is Mark John Fernee, a physicist at the University of Queensland. I’ve learned a lot of science from an approach based on scepticism. For example, I was sceptical about relativity theory: that clocks could really slowly down and why did they slow down for one observer but not another, as demonstrated in the famous twin paradox. In fact, it’s nature’s paradoxes that provide the incentive to try and understand it to the extent that one can. 

 

Another example is quantum mechanics. For a long time, I followed David Bohm’s approach, which was really an attempt to bring QM back down to Earth so-to-speak. I believe that both Schrodinger and Einstein also believed in a ‘hidden-variables’ approach.

 

I finally gave this up when I concluded that QM and classical physics obey different rules: superposition and entanglement are not part of classical physics, either experimentally or mathematically. And I found that special relativity only made sense in the context of general relativity (which I discuss in more detail below).

 

And then you have the combination of special relativity with QM, which, from a mathematical perspective, allows anti-particles to exist. As Fernee points out, because an anti-particle can be represented mathematically by a particle going backwards in time, it ensures that charge is conserved by time’s arrow. In other words, you can turn an electron into a positron, or vice versa, by reversing time, which is why it’s never observed.

 

One of the paradoxes I now struggle with is that, according to special relativity, you can have different ‘nows’ in different parts of the universe. This is why most, if not all physicists, argue that the universe is completely deterministic, if someone’s future can be hypothetically observed by someone else’s motion. I confess I’m very sceptical about this. What they're saying is that the ‘now’ in some other part of the Universe is changed by an observer’s motion locally. Fernee quotes Roger Penrose in response to a question: can we theoretically teleport to some other location in the Universe instantaneously, like we see in science-fiction movies? According to Fernee (quoting Penrose), if you could and then teleport back, you might arrive before you left, because a random movement by you could change the ‘now’ in that distant part of the universe into your past. I’m assuming this can be demonstrated mathematically; it’s a consequence of simultaneity changing depending on the observer, according to special relativity. 

 

I’ve discussed this in other posts. I like to point out that, where there’s a causal relationship, the sequence of events can’t be changed, dependent on an observer’s perspective. Which makes me wonder: does a sequence change, dependent on an observer’s perspective, when they’re not causal? Is it possible that there is a sequence of events independent of any observer?

 

And this leads to another paradox that is hardly ever addressed which is that, despite this proliferation of ‘nows’, dependent on observers’ perspectives, we have an ‘age of the Universe’. I actually raised this with Fernee in a dialogue I had with him, and he referenced a paper by Tamara M. Davis and Charles H. Lineweaver at the University of New South Wales, titled, Expanding Confusion: Common Misconceptions of Cosmological Horizons and the Superluminal Expansion of the Universe. I’ve lost the link, and I can no longer even find the post on Quora, but I downloaded the paper, which is 24 pages long, not including the references.

 

Of course, it’s an academic paper, yet I found it easier to follow and understand than I might have expected. Which is not to say I have a full grasp of it, but I feel I can relay some of its most pertinent points. The paper is dated 13 November 2013, so it seems apt I’m writing about it on 13 Nov, 2021. Firstly, the cosmological model of the Universe the authors discuss, is referred to as ΛCDM cosmology (Lambda-CDM cosmology), where CDM is an acronym for Cold Dark Matter. Lambda (Λ) is the cosmological constant that gives us ‘dark energy’, so the model includes both dark energy and dark matter.

 

As the title suggests, the authors discuss misconceptions found in the literature concerning the horizon problem, and at the end they provide a list of examples, including one by Richard Feynman (1995), 

 

“It makes no sense to worry about the possibility of galaxies receding from us faster than light, whatever that means, since they would never be observable by hypothesis.” 

 

And this one by Paul Davies (1978): 

 

“. . . galaxies several billion light years away seem to be increasing their separation from us at nearly the speed of light. As we probe still farther into space the redshift grows without limit, and the galaxies seem to fade out and become black. When the speed of recession reaches the speed of light we cannot see them at all, for no light can reach us from the region beyond which the expansion is faster than light itself. This limit is called our horizon in space, and separates the regions of the universe of which we can know from the regions beyond about which no information is available, however powerful the instruments we use.” 

 

What the authors expound upon in the main body of their text is that there are, in effect, a number of horizons, which makes these statements erroneous at best. To be fair to both Feynman and Davies, the ΛCDM model of the Universe wasn’t known at the time. Dark energy wasn’t officially ‘discovered’ until 1998. Davis and Lineweaver provide diagrams to show these various horizons, which I can’t duplicate here, and if I did, I’d have trouble explicating them. But basically, there is a particle horizon, which is the limit of the observable universe, the Hubble sphere, which is the boundary of the expanding universe (where it equals c) and the event horizon. (To quote the authors: Our event horizon is our past light cone at the end of time, t = ∞ in this case.) There is a logical tendency to think they should all be the same thing, but they’re not, as the authors spend a good portion of their 24 pages expounding upon. To quote again:

 

The particle horizon at any particular time is a sphere around us whose radius equals the distance to the most distant object we can see... Our effective particle horizon is the cosmic microwave background (CMB).

 

Whereas:

 

Hubble sphere is defined to be the distance beyond which the recession velocity exceeds the speed of light, DHS = c/H. As we will see, the Hubble sphere is not an horizon. Redshift does not go to infinity for objects on our Hubble sphere (in general) and for many cosmological models we can see beyond it... The ratio of ∼ 3/1 is the ratio between the radius of the observable universe and the age of the universe, 46 Glyr/13.5 Gyr.

 

What you have to get your head around is that the universe is dynamic, and given the time it takes for light to reach us from the edge of the Universe, both the edge and the objects (we’re observing) have moved on, quite literally. This means we can observe objects over the horizon so-to-speak. But it’s even more complex than that, because the Hubble sphere, which is expanding, can overtake photons that were emitted beyond the horizon but are travelling towards us. According to the authors, we can observe objects that are ‘now’ travelling at superluminal speeds relative to us. 

 

This is how the authors explain it:

 

Light that superluminally receding objects emit propagates towards us with a local peculiar velocity of c, but since the recession velocity at that distance is greater than c, the total velocity of the light is away from us. However, since the radius of the Hubble sphere increases with time, some photons that were initially in a superluminally receding region later find themselves in a subluminally receding region. They can therefore approach us and eventually reach us. The objects that emitted the photons however, have moved to larger distances and so are still receding superluminally. Thus we can observe objects that are receding faster than the speed of light. 

 

One of the most illuminating aspects of their dissertation, for me, was that one needs to use a general relativistic (GR) derivation of the Doppler redshift and not a special relativistic (SR) derivation, which is usually used. They show graphically that the SR and GR derivations diverge, especially for further distances. On the same graph, they show how a non-relativistic Doppler shift, which would be ‘tired light’ (authors’ term) is actually a horizonal line, so nowhere near. The graph, of course, shows these curves against observations of super novae. As they explain it:

 

The general relativistic interpretation of the expansion interprets cosmological redshifts as an indication of velocity since the proper distance between comoving objects increases. However, the velocity is due to the rate of expansion of space, not movement through space, and therefore cannot be calculated with the special relativistic Doppler shift formula. 

 

What they are saying is that there is a distinction between the movement of the objects in space and the movement of space itself. For me, this ends the debate about whether ‘space’ is an entity or just the distance between objects. As much as I admire and respect Viktor T Toth, I’ve always had a problem with his argument that space ‘doesn’t expand’, but only the objects ‘move’ thus creating more space between them. The Hubble sphere, as I understand it, is where space equals c.

 

Later in their paper, Davis and Lineweaver describe how they derived their equation for the GR redshift.

 

For the observed time dilation of supernovae we have to take into account an extra time dilation factor that occurs because the distance to the emitter (and thus the distance light has to propagate to reach us) is increasing.

 

In other words, in calculating the redshift of a ‘comoving galaxy’, they also have to take into account the constant expansion of space in the photon’s journey to the observer. 

 

....the peculiar velocity of a photon, Rχ ̇, is c. Since the velocity of light through comoving coordinates is not constant (χ ̇ = c/R), to calculate comoving distance we cannot simply multiply the speed of light through comoving space by time. We have to integrate over this changing comoving speed of light for the duration of propagation. Thus, the comoving coordinate of a comoving object that emitted the light we now see at time t is attained by integrating.  (χ ̇is the time dependent expansion of space and R is the radial distance). 

 

Notice that in contrast to special relativity, the redshift does not indicate the velocity, it indicates the distance. That is, the redshift tells us not the velocity of the emitter, but where the emitter sits (at rest locally) in the coordinates of the universe. 

 

In other words, when we integrate χ ̇, we get χ, which is distance. The authors provide another equation for determining the velocity.

 

Now, one of the obvious aspects of this whole exercise is that they are calculating a redshift across space that changes over time, so what does time mean in this context?

 

This is how the authors explain it, just before their conclusion:

 

Throughout this paper we have used proper time, t, as the temporal measure. This is the time that appears in the RW metric and the Friedmann equations. This is a convenient time measure because it is the proper time of comoving observers. Moreover, the homogeneity of the universe is dependent on this choice of time coordinate — if any other time coordinate were chosen (that is not a trivial multiple of t) the density of the universe would be distance dependent. Time can be defined differently, for example to make the SR Doppler shift formula correctly calculate recession velocities from observed redshifts (Page, 1993). However, to do this we would have to sacrifice the homogeneity of the universe and the synchronous proper time of comoving objects.

 

I find it interesting that they adopt a ‘proper time’ for the whole universe. It makes one wonder what ‘now’ really means.

 

Footnote 1: I want to point out that in their acknowledgements, Davis and Lineweaver reference Brian Schmidt, who received a joint Nobel Prize for his work in empirically confirming dark energy, or the cosmological constant (Λ).

Footnote 2: You can download the paper here.

Addendum: This is a video by someone (who knows more than me) and doesn’t give his name. I posted a video by him before, regarding the question: Is gravity a force? His videos on Penrose tiling and the Feigenbaum constant are among the best.

 

In this video, he refutes my claim, arguing that space doesn’t expand. He makes one very compelling point that if space expanded so would atoms and so would we. Victor T Toth makes the exact same point, and I’d have to agree. The size of all atoms is determined by h (Planck's constant), which doesn't change with the expansion of the Universe. I might add that this presenter and Toth disagree on whether gravity is a force or not, so physicists don’t always agree, even in the same field, like cosmology.

 

In the video, he argues that there are 3 types of Doppler shift and contends that they are actually all the same. Most intriguing was the thought experiment that someone in ‘free fall’ wouldn’t see the Doppler shift that another observer would. In other words, it’s observer dependent.

 

But there is a spacetime metric or manifold, which forms the basis of general relativity theory (GR) and this can warp and curve (according to said theory). In fact, there is a phenomenon called ‘frame dragging’, where spacetime is dragged around by a spinning black hole. Light is always c in reference to this spacetime manifold. So when ‘space’ reaches the speed of light at the horizon relative to us, light is still c in that reference frame, even though it is expanding away from us at c or more. Space can travel faster than light, even though massive particles can’t, which is why ‘inflation’, proposed at the birth of the Universe, is possible.

 

Getting back to the Doppler shift the authors cite in their paper, they use a GR Doppler shift, which I believe isn’t covered in the video.

A philosophical exploration of Type A and Type B time

 This arose from a question referred to me on Quora. As part of my discussion, I wondered into philosophical territory originally posited over a century ago by a forgotten philosopher, J.M.E. McTaggart, thanks to A.C. Grayling (English philosophers seem to have a predilection for using initials). It seems to fit seamlessly into my own particular philosophy on the relationship between time and consciousness.

 

The original question on Quora, asked by Adriana Moraes (from Sao Paulo, Brazil):

 

How does the past, present, and future exist simultaneously?

 

I don’t believe they do. In fact, I contend that past, present and future are only meaningful concepts in some creature’s mind; which means that I don’t believe it’s a cognitive state unique to humanity.

 

We are only aware of the past because we have memories. In fact, without memory, you wouldn’t know you are conscious. Consciousness exists in a constant present, so time for us is always ‘now’. This, of course, applies to all sentient creatures. For all events that we witness or observe, ‘now’ is ephemeral – they become the past as soon as they happen - which is demonstrated every time someone takes a photo. We say it ‘freezes time’, when in fact, it records an event that would otherwise vanish.

 

Past, present and future require a reference point, and consciousness provides that reference point. We imagine futures, and curiously, the same part of the brain that imagines what might happen, conjures up memories of what has happened. This makes sense when one realises that we attempt to predict the future based on what we have experienced in the past. 

 

Raymond Tallis, who has a background in neuroscience and writes books as well as a regular column in Philosophy Now, makes the observation that our ability to ‘imagine’ future ‘possibilities’, and select one to make ‘actual’, is the very definition of free will, only he calls it 'agency'.

 

In 1908, an Oxford philosopher, J.M.E. McTaggart published a paper titled, On the Unreality of Time in the journal, Mind (ref: A.C. Grayling, The History of Philosophy, 2019). McTaggart argued that there are 2 types of time: Type A, which is based on using the ‘present’ as a reference point for ‘past-present-future’; and Type B, which is just the ordering of events into ‘earlier than/later than’. He contended, in effect, that because ‘now’ is constantly changing, you get contradictions with Type A and Type B (which is perceivably 'fixed'). I’ve over-simplified his argument for brevity, and given it my own interpretation, which is that you can’t have both Type A and Type B. However, I contend that Type B time is just Type A time without consciousness, which resolves that particular paradox.

 

Most physicists, if not all, believe that the past, present and future are all fixed, because, according to Einstein’s special theory of relativity, ‘now’ is totally subjective. This is the so-called ‘block universe’, which is a logical consequence of treating time as a spatial dimension, giving us space-time.

 

You can observe time as a dimension by looking at the night sky and seeing stars hundreds, if not thousands of years, in the past. This means that hypothetical observers in different parts of the Universe see a different ‘now’ and will observe events occurring in different sequences. This is a logical consequence of the finite speed of light. However, causally related events must happen in an objective sequence, irrespective of observers. This is Type B time, as defined by McTaggart. We are able to deduce causality of events that have happened in our past, which gives us theories of cosmology and evolution. This has to be compatible with Type A time, which is dependent on the fact that we all live in the present all of the time. 

 

Whether our present is different to someone else’s present (somewhere else in the Universe) just means that their Type A experience of time is different to ours, but Type B time occurs regardless of conscious observers.

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.