The edge of time

This is a contentious idea, despite the fact that we all believe we experience it all the time. Many physicists, including ones I admire, and whom I readily admit know a lot more than me (like Sabine Hossenfelder), believe that ‘now’ is an illusion; or (in the case of Paul Davies) that it requires a neurological explanation rather than a physical one. I will go further and claim there is an edge of time for the entire universe.
 
I made the point in a previous post that if you go on YouTube, you’ll find discussions with physicists who all have their own pet theories that are at odds with virtually everyone else, and to be honest, I can’t fault them, and I’m pleased that they’re willing to share their views.
 
Well, I’m not a physicist, but this is my particular heretical viewpoint that virtually no one else agrees with, with the additional caveat that they all have more expertise than me. They will tell you that I’m stuck in 19th Century physics, but I believe I can defend myself against that simple rebut.
 
During COVID lockdown in 2021, I did a series of online courses through New Scientist, including one on The Cosmos, where one of the lecturers was Chris Impey (Distinguished Professor, Department of Astronomy, University of Arizona) who made the point that the Universe has an ‘edge in time’, but not an edge in space. He might have used the word ‘boundary’ instead of ‘edge’, which would be more appropriate for space. In fact, it’s possible that space is infinite while time is finite, which means that the concept of spacetime might have limited application, but I’m getting ahead of myself.
 
The one other person I’ve read who might (partly) agree with me is Richard Muller, who cowrote a paper with Shaun Maguire, titled Now, and the Flow of Time, as well as a book, NOW; The Physics of Time, which I’ve read more than once. Basically, the edge of time on a cosmic scale is the edge of the Big Bang (which is still happening). What I’m saying is that there is a universal ‘Now’ for the entire universe, which is one of the most heretical ideas you can hold. According to modern physics, ‘Now’ is completely subjective and dependent on the observer – there is no objective Now, which is what I challenge.
 
There is a way in which this is correct, in that different observers in different parts of the Universe see completely different things (if they’re far enough apart) and would even see different horizons for the Universe. In fact, it’s possible that an observer who is over the horizon to us will see objects we can’t see, and of course, wouldn’t see us at all. This is because objects over the horizon are travelling away from us faster than the speed of light.
 
Because the speed of light is finite, the objects that we ‘observe’ millions or billions of light years away, are commensurately that much older than we are. And it follows from this logic, that if anyone could observe Earth from these same objects, they would see it equally old compared to what we see. This means that everyone sees a different now. This leads to the logical question: how could an objective ‘now’ exist? I like to invoke Kant that we cannot know the ‘thing-in-itself’, only our perception of it.
 
And I invoke Kant when I look at relativity theory, because it’s inherently an observer-dependent theory. I would contend that all physics theories are epistemic, meaning they deal with knowledge, rather than ontic, which is what is really there. Some argue that even space and time are epistemic, not ontic, but I disagree. The dimensions of space and time determine to a large extent what sort of universe we can live in. A point made by John Barrow in his book, The Constants of Nature.
 
In a not-so-recent post, I explained the famous pole-in-the-barn paradox, where 2 different observers see different things (in fact, measure different things) yet, in both cases, there is no clash between the pole and the barn (or in the example I describe, a spaceship and a tunnel). One of my conclusions is that it’s only the time that changes for the 2 observers, and not the space. Instead, they measure a different ‘length’ or ‘distance travelled’ by using their clocks as rulers. But it also implies that one of the observers is more ‘privileged’ than the other, which seems to contradict the equivalence principle. But I can make this claim because there is a reference frame for the entire universe, which is provided by the CMBR (cosmic microwave background radiation). This is not contentious, because we can even measure our velocity relative to it by using the Doppler effect, hence our velocity relative to the entire universe.
 
But there is another famous and simple experiment that provides evidence that there is an overall frame of reference for the Universe, which philosopher of science, Tim Maudlin, called ‘the most important experiment in physics’. If you were to go to the International Space Station and spin an object, it would be subject to the same inertial forces as it would on Earth. So what’s it spinning in reference to? The spaceship, its orbit around Earth, or the entire cosmos? I’d say, the entire universe, which is obviously not spinning itself, otherwise it would have a centre. Of course, Einstein knew this, and his answer was there is no absolute time or space but absolute spacetime.
 
I raised this earlier, because, if time is finite and space infinite, the concept of absolute spacetime breaks down, at least conceptually. But space doesn’t have to be infinite to have no boundary. In fact, it’s either open and infinite or closed and finite, albeit in 3 dimensions. To provide a relatable analogy, the Earth’s surface is finite and closed, but in 2 dimensions. Marcus du Sautoy made the point that, if the Universe is spatially infinite, we might never know.
 
The other point is that you could have clocks running at different rates dependent on where they are in the Universe, yet there could still be a universal Now. This is implicit in the famous twin paradox thought experiment. I like to point out that when the twins reunite they have lived different durations of time, yet agree where they are in time together. This means you can have a universal Now for the universe while disagreeing on its age; if you lived near a massive black hole, for instance.
 
In the same way observers can travel different distances to arrive at the same destination, they can travel different time intervals as well. In fact, they would agree they’ve travelled the exact same spacetime, which is why relativity theory argues you can only talk about spacetime combined rather than space and time separately. But I argue that it’s the clock that changes and not space, where the clock is the ruler for space.

The fly-in-the-ointment is simultaneity. According to relativity theory, simultaneity is completely dependent on the observer, but again, I invoke Kant. There could be an objective simultaneity that can’t be observed. I’ve written on this before, so I’ll keep it brief, but basically, you can have a ‘true’ simultaneity, if both the observer and the events are in the same frame of reference. And you can tell if you’re not, by using the Doppler effect. Basically, the Doppler effect tells you if the source of the signals (that are apparently simultaneous) are in the same frame of reference as you. If they’re not, then they’re not simultaneous, which infers there is an objective simultaneity. Whether this applies to the entire universe is another matter.

You may be familiar with this diagram.

 

 
I want to make a couple of points that no one else does. Firstly, everything outside the past light cone is unobservable (by definition), which means relativity theory can’t be applied, yet people do. As I said earlier, relativity is epistemic and all epistemic theories (or models) have limitations. In other words, I contend that there is an ontology outside the light cones that relativity theory can’t tell us anything about (I discuss this in more detail in a post appositely titled, The impossible thought experiment).
 
Secondly, the so-called ‘hypersurface’ is a fiction, or at best, a metaphor. Yet Brian Greene, to give one example, discusses it and graphically represents it as if it’s physically real. If ‘Now’ is the edge of the Big Bang, it suffuses the entire universe (even if it’s physically infinite), which means it’s impossible to visualise.
 
Let’s talk about another epistemic theory, quantum mechanics. In fact, the ontology of QM has been an open debate for more than a century. I recently watched a discussion between Matt (from PBS Space Time) and Mithuna Yoganathan (of Looking Glass Universe), which is excellent. It turns out they’re both from Melbourne, which is where I’m writing this. I figured Mithuna was Aussie, even though she’s based in London, but I didn’t pick Matt’s accent. I have to admit he sounds more Australian in his conversation with her. Towards the end of the video, they readily admit they get very speculative (meaning philosophical) but Mithuna provides compelling arguments for the multiple worlds interpretation (MWI) of QM. Personally, I argue that MWI doesn’t address the probabilities which is intrinsic to QM. Why are some worlds more probabilistic than others? If all outcomes happen in some universe somewhere, then they all have a probability of ONE in that universe. If there are an infinite number of universes then probabilities are nonsensical.
 
If you go to 37.10m of the video where Mithuna talks about the Schrodinger equation and the ‘2 rules’, I think she gets to the nub of the problem, and at 38.10 puts it into plain English. Basically, she says that there are either 2 rules for the Universe or you need to reject the ‘measurement’ or ‘collapse’ of the wave function, which means accepting MWI (the wave function continues in another universe), which she implies without saying. She says the 2 rules makes ‘the Copenhagen interpretation untenable’. I find this interesting, because I concluded many years ago that the Universe obeys 2 sets of rules.
 
My argument is that one set of rules, determined epistemically by the Schrodinger equation, describes the future and the other set of rules, which is classical physics and is determined by what we observe, describes the past.
 
A feature of QM, which separates it from classical physics, is entanglement and non-locality. Non-locality means it doesn’t strictly obey relativity theory, yet they remain compatible (because you can’t use entanglement to transmit information faster-than-light). In fact, Schrodinger himself said that “entanglement is the characteristic trait of quantum mechanics, the one that enforces its entire departure from classical lines of thought.” In other words, it obeys different rules to classical physics, with or without ‘measurement’.
 
MWI effectively argues that superposition exists in reality, albeit in parallel universes, whereas I contend that it only exists in the future. The wave function describes all of these possibilities, and via the Born rule, gives them probabilities. But when we observe it, which axiomatically puts it in the past, there is only ONE and there is no longer any superposition.
 
All physicists agree that entanglement, in principle, can apply to objects on opposite sides of the Universe. In fact, Schrodinger’s equation, in principle, can describe a wave function for the entire universe, which is why I’ve half-jokingly called it God’s equation, and have it tattooed on my arm.
 
I contend (though, as far as I know, no one agrees with me) that entanglement across the entire universe only makes sense if there is a universal Now for the entire universe. A Now that separates QM future superpositions (described by the wave function in Schrodinger’s equation) from past ‘observables’ in classical physics.