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CPT-Symmetric Universe

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Celebaelin
1390951.  Sun Sep 26, 2021 1:36 am Reply with quote

CPT (charge, parity, and time) symmetry



Quote:
For the past year, Turok and his Perimeter Institute colleagues Latham Boyle and Kieran Finn have been developing a new cosmological model that has much in common with the no-boundary proposal. But instead of one shuttlecock, it envisions two, arranged cork to cork in a sort of hourglass figure with time flowing in both directions. While the model is not yet developed enough to make predictions, its charm lies in the way its lobes realize CPT symmetry, a seemingly fundamental mirror in nature that simultaneously reflects matter and antimatter, left and right, and forward and backward in time. One disadvantage is that the universeís mirror-image lobes meet at a singularity, a pinch in space-time that requires the unknown quantum theory of gravity to understand. Boyle, Finn and Turok take a stab at the singularity, but such an attempt is inherently speculative.

https://www.quantamagazine.org/physicists-debate-hawkings-idea-that-the-universe-had-no-beginning-20190606/

Quote:
We propose that the state of the universe does {\it not} spontaneously violate CPT. Instead, the universe after the big bang is the CPT image of the universe before it, both classically and quantum mechanically. The pre- and post-bang epochs comprise a universe/anti-universe pair, emerging from nothing directly into a hot, radiation-dominated era. CPT symmetry selects a unique QFT vacuum state on such a spacetime, providing a new interpretation of the cosmological baryon asymmetry, as well as a remarkably economical explanation for the cosmological dark matter. Requiring only the standard three-generation model of particle physics (with right-handed neutrinos), a Z2 symmetry suffices to render one of the right-handed neutrinos stable. We calculate its abundance from first principles: matching the observed dark matter density requires its mass to be 4.8◊108 GeV. Several other testable predictions follow: (i) the three light neutrinos are Majorana and allow neutrinoless double β decay; (ii) the lightest neutrino is massless; and (iii) there are no primordial long-wavelength gravitational waves. We mention connections to the strong CP problem and the arrow of time.

CPT-Symmetric Universe Latham Boyle, Kieran Finn, Neil Turok
Phys. Rev. Lett. 121, 251301 (2018)
https://arxiv.org/abs/1803.08928

I'm nervous of misinterpreting what I've read on this since it's beyond my level of understanding to be certain of the implications but I think they're suggesting something like this.

 
CB27
1391004.  Sun Sep 26, 2021 3:41 pm Reply with quote

Because of the language used, it's hard for me to completely comprehend, but I find it impossible to consider the idea of a universe and anti universe inhabiting different "spaces" as that description and model seem to suggest (unless I got it completely wrong).

It would make more sense to me if the two were enmeshed together, inhabiting the same space, but perhaps separated by a different phase in time, thereby allowing for dual expectations as defined by quantum mechanics.

Or I could be talking rubbish because my understanding is very limited :)

 
ali
1391027.  Sun Sep 26, 2021 10:36 pm Reply with quote

Recent developments suggest that Majorana neutrinos may be necessary to explain experimental results, though as I understand it neutrinoless double β decay remains unobserved.

 
Celebaelin
1391243.  Tue Sep 28, 2021 4:36 pm Reply with quote

OK, since we're embarking on this let's see what YouTube (mainly in the guise of Sabine Hossenfelder and of Matt O'Dowd) can tell me about the physics stuff I've heard of but don't really get.

What does the universe expand into? Do we expand with it?

Not as enlightening as I was hoping for but fair enough.

Is Time Real?

Do the Past and Future Exist?

Time: Do the past, present, and future exist all at once?

This gets into the human perception of time rather than what the physicists posit based on the position and velocity of the observer.

The general notion seems to be about the capacity to observe the universe and whether it exists if we canít observe it. There are events we will be able to observe in the future as we move into their light cone; as a corollary distant events we can currently observe will move out of our light cone because expansion will take them out of our light cone. Do those two sets of events not yet exist or cease to have existed when they are not observable?

So is this the point about past present and future being simultaneous or do some physicists actually think that an individual observerís past, present and future occur simultaneously from the viewpoint of any one single* observer? Iíve not found any indication that anyone believes that but that has definitely been the impression Iíve gained (and found difficult to rationalise if not to conceptualise).

*I want to add Ďrelatively staticí to that as an observer who had moved at or close to the speed of light would achieve a position where the future relative to his start point would be observable.

Does Consciousness Influence Quantum Mechanics?

https://en.wikipedia.org/wiki/Sabine_Hossenfelder
https://en.wikipedia.org/wiki/Matt_O%27Dowd_(astrophysicist)
https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time)
https://en.wikipedia.org/wiki/Von_Neumann%E2%80%93Wigner_interpretation

I may get around to trying gain some further insight into eg warp drive theory (already looked at a bit of it), synchronicity, the Pauli exclusion principle and maybe some other bits at a later point though interested parties could accelerate the process by posting links they deem informative.


Last edited by Celebaelin on Thu Sep 30, 2021 10:57 am; edited 1 time in total

 
dr.bob
1391308.  Wed Sep 29, 2021 9:27 am Reply with quote

Celebaelin wrote:
So is this the point about past present and future being simultaneous or do some physicists actually think that an individual observerís past, present and future occur simultaneously from the viewpoint of any one single* observer? Iíve not found any indication that anyone believes that but that has definitely been the impression Iíve gained (and found difficult to rationalise if not to conceptualise).


I think this is a result of 4-dimensional space-time as described by Einstein's Theory of Relativity.

This describes time as simply a fourth dimension of the universe that we move through in exactly the same way we move through space. The maths of this is elegant and consistent. The fact that time slows down as your velocity increases is a direct result of rotating a vector through 4-dimensional space.

However, if time is simply another dimension like the three dimensions of space, then it implies that all of time exists and we move through it, in the same way that the other end of my street already exists and doesn't have to wait for me to walk down to it for it to pop into existence.

Clearly this causes some problems with our experience of time, since we cannot access anything other than the bit of time we're currently in. If that's a fundamental property of time, then it needs to be explained by relativity. However, it may simply be a failure on our part to perceive things that are already there, in the same way that a dog can't see colours even though they definitely exist.

 
Jenny
1391317.  Wed Sep 29, 2021 9:42 am Reply with quote

I am fascinated by stories involving time travel (and if any of you haven't come across Jodi Taylor's "Chronicles of St Mary's" series, or Connie Willis's books, I heartily recommend them) but I gather nobody thinks that is at all likely. It certainly raises issues of pre-determination, and also of multiple universes (in one you do one thing, in another a different thing), which becomes more unlikely the more you think about the number of people in the world and the different choices they might make.

 
PDR
1391329.  Wed Sep 29, 2021 10:47 am Reply with quote

I've always thought Predestination (the movie) was a very interesting take on time travel possibilities (especially time loops), but the problems of time travel are surely as much inertial as paradoxical. You need to pick a frame of reference, but even if we just anchor it to the centre of our galaxy our solar system has a tangential velocity of over 720,000mph. After 24 hours that gives us a distance of over 17 million miles between where *here* is now and where *here* will be tomorrow. So if you want to travel forwards to be in your house tomorrow then you need to travel 24 hours in time plus 17 million miles in space.

That leads to the meta-question of the journey time - how long do you want to spend travelling? If you want to take one leisurely hour on the journey then you will need to *average* 17 million miles per hour, half that time accelerating and the other half decelerating. So if we consider a journey of 8.5million miles in 30 minutes:

s = 1/2 at^2, so

a = 2s/t^2

s = 17,000,000 * 1,609 = 2,735,000,000 metres
t = 30 minutes = 1,800 seconds

a = (2 * 2,735,000,000) / (1,800^2)

= 1,688m/sec or 172G

So the leisurely stroll into the future would involve half an hour accelerating at 172G followed by another half hour decelerating back down again, also at 172G*. This would leave you compressed into your seat, which helps to explain why travel can be such a high pressure experience.

PDR

* this is a very rough approximation because (a) you would probably want to ramp the seed up and down in a more progressive rather than sudden manner, (b) it ignores the detail that you were already doing 720,000mph anyway, and (c) it involves travelling at a speed that peaks at around a tenth of the speed of light, so there would be some lorenz factor corrections (time dilation etc)

 
CB27
1391341.  Wed Sep 29, 2021 11:21 am Reply with quote

I've always thought time travel itself, while great for fiction, is not something I can conceive of IRL for reasons as stated above, and more.

1. The distance covered between two different points in time.
2. Where does the matter that allows you to exist at a different come from?
3. If you do somehow account for the extra matter to move between time, how do you maintain the momentum of particles on a molecular level to create the atoms and molecules, so that when you're transported you're not simply turned into some sort of matter soup.
4. How do you account for all events after an event if you can go back and change it.

So for some of those reasons, I suppose I could accept moving "sideways" into a different dimension that's a carbon copy of ours, except at a different age since the start of the universe. It doesn't explain away some of the issues still, but I imagine a disc full of rings (like the rings of a tree). Each ring is an identical dimension, and they each experience the age of the universe from start to end for the same length of time regardless if they're an inner ring or outer ring, but relative to the centre of the disc they're travelling at different speeds so if at any time you move from one disc to another, it's like travelling back and forth in time, but of course you being there already affects it in a way that might be different from other dimensions.

The alternative is that "time travel" is simply a way of looking further back in time through some means, perhaps collecting particles of light at a distance location and being able to "boost" the signal to view where those particles last bounced off.

 
PDR
1391347.  Wed Sep 29, 2021 11:32 am Reply with quote

Of course just *viewing* the past is an entirely different matter. Scientists have developed devices that are mounted in various locations on the Isle of Wight which feed a website on which you can browse authentic views of what life was like there in the 1950s. They call them "webcams".

PDR

 
CB27
1391357.  Wed Sep 29, 2021 12:42 pm Reply with quote

The US likes to do things even bigger, they've got webcams that can let you see what life and attitudes were like 170 years ago, though mostly in Republican led counties.

 
Jenny
1391365.  Wed Sep 29, 2021 2:41 pm Reply with quote

Actually it's an immersive experience, especially if you're female. Go and live there and you'll find out.

 
dr.bob
1391419.  Thu Sep 30, 2021 8:40 am Reply with quote

CB27 wrote:
2. Where does the matter that allows you to exist at a different come from?


Slight typo there. I assume you meant to write: "Where does the matter that allows you to exist at a different time come from?"

This question makes no sense if you view time as simply another dimension in four-dimensional spacetime as described by the Theory of Relativity. It would be exactly like asking "Where does the matter that allows you to exist in a different place come from?"

The answer, of course, is that it doesn't come from anywhere. It simply moves from one location to the other.

CB27 wrote:
4. How do you account for all events after an event if you can go back and change it.


This is, of course, the biggest problem as it would violate the principle of causality. As far as we can tell, the principle of causality is a fundamental basis of physics and violating it would cause many problems.

However, bear in mind that I said "as far as we can tell". It may be that we haven't fully understood the universe yet and there may be some theory that explains how the principle of causality can be sidestepped without ruining the whole of physics. If we were to discover this, then one major obstacle to time travel would be removed.

 
Jenny
1391430.  Thu Sep 30, 2021 9:58 am Reply with quote

Most of the fiction writers I have come across who deal with time travel (sorry but this is as close as I can get to the concept...) seem to deal with that by asserting a multi-universe capability. A character can die in one world but survive in another.

The one constant I've come across in the fictional descriptions is not being able to meet yourself in an earlier existence - being able to have two of you in the same area at the same time seems to be a massive no-no.

 
Celebaelin
1391445.  Thu Sep 30, 2021 11:15 am Reply with quote

Celebaelin wrote:
The general notion seems to be about the capacity to observe the universe and whether it exists if we canít observe it. There are events we will be able to observe in the future as we move into their light cone; as a corollary distant events we can currently observe will move out of our light cone because expansion@ will take them out of our light cone#. Do those two sets of events not yet exist or cease to have existed when they are not observable?

@ The expansion being referred to which I cite above must be the extremely rapid expansion of the early universe rather than the rate at which the universe is currently expanding... mustn't it?

# I've spent some time thinking about light 'cones' now and for those like me who are hard of understanding in such matters some explanation might be of use. The depiction of light cones substitutes time for one of the other dimensions of space-time to arrive at the cone - the hourglass-like depiction exists with the direction of the time axis preserved in the great celery vase of the universe with time as the height of the vase (after time begins anyway).

It seems to me that the future light cone of Wiki's illustration (which confirms my thinking) defines the limits of movement not of observation and that the relevant criterion for observation of 'new' objects is that those objects enter our past light cone. If our instruments were good enough our observable universe would extend in a sphere (the exact shape would be modified by obstacles to observation and the curvature of space-time by gravity) around our planet with a radius of the speed of light multiplied by the duration of the existence of time in the universe (this is thought to be less than the duration of the existence of the universe but, for obvious reasons, to an immeasurable extent).

https://en.wikipedia.org/wiki/Light_cone

Wiki seems to have reversed the direction of the arrow of time on the past portion of the time axis; this is not what is happening as time proceeds from bottom to top in our universe as things stand.

 
CB27
1391449.  Thu Sep 30, 2021 11:44 am Reply with quote

dr.bob wrote:
CB27 wrote:
2. Where does the matter that allows you to exist at a different come from?


Slight typo there. I assume you meant to write: "Where does the matter that allows you to exist at a different time come from?"

This question makes no sense if you view time as simply another dimension in four-dimensional spacetime as described by the Theory of Relativity. It would be exactly like asking "Where does the matter that allows you to exist in a different place come from?"

The answer, of course, is that it doesn't come from anywhere. It simply moves from one location to the other.

It's a typo, but I meant to say dimension rather than time.

The issue I have here is that I I see each dimension as a carbon copy of a universe in that they contain the same amount of matter from the beginning. Matter doesn't come from nothing, nor does it extinguish to nothing, it merely changes state.

Therefore, if we take matter from one dimension and add it to another dimension, neither of them are true copies of the same universe to each other or to all other dimensions, so they are no longer dimensions of the same universe.

 

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