[geordief (OP)]

Watching a Horizon programme last night on BBC 4 (Sean Caroll was one of the contributers)

Apparently the Cosmic Microwave Background Map is like an expanding bubble around anywhere in our "neighbourhood" and its features have now been mapped in enough detail to "draw" a huge triangle from here to there.

The triangle ,according to the programme is evidence that  space (spacetime?) is probably flat and as a result the universe outside the observable part is  of infinite extent.

What might be the implications if this,startlingly  is true and can we now posit this provisional result as a stone to build our edifice of how "everything" works.

Can we ditch the "universe may be finite" for good unless we get  some new unexpected observations in the coming years or centuries?

[alancalverd]

The observable part of the universe is obviously finite if it is expanding, but it would be absurd to state that there is no unobservable volume outside, or to assert that the unobservable volume is also finite.

[geordief (OP)]

But can we begin to tentatively assume that the observable universe may well  be part of an (dynamic) infinite structure?

Rather than hedging our bets as it were,can we just let it sink in to our "world view" that this ,or something very similar can be the starting block  that all our other ideas and theories have to accord with?

A bit like Einstein and the invariance of the speed of light.Just accept it and build around it.

It makes me wonder where the energy "came from" to keep "all this" going.

Is it related to asymmetry?

[Halc]

But can we begin to tentatively assume that the observable universe may well  be part of an (dynamic) infinite structure?

That (the infinite part) has pretty much been the assumption all along, and all this latest finding only shows that it is flat to more zeros than had previously been measured. Any positively curved space would imply a finite volume just like Earth's surface is positively curved and thus has finite area despite the limited extent of the visible part of it. There's no edge. You can travel indefinitely and never get to a boundary, and yet the area is finite.

So while the assumption has always been an infinite universe, they've never really been able to put sufficient nails in the finite-volume model. This is just one more nail in that coffin. The finite models don't explain anything better than the infinite models.

I don't know what you mean by dynamic. Yes, the state at a given time is different than a state at a different time, but the 'state' isn't the structure, the latter being the whole of spacetime with time as part of the structure, so the structure itself isn't something that changes, and is thus questionably describable as 'dynamic'.

[Kryptid]

The implications of an infinite universe are pretty startling, actually. When you have an infinite amount of matter and energy with a relatively random distribution throughout space, then every possible scenario will have happened an infinite number of times in the past (so long as the scenario doesn't require longer than the current age of the Universe to occur) and will continue to happen an infinite number of times in the future.

Anything you can imagine that doesn't violate the laws of physics (except the 2nd law of thermodynamics, which is a statistical law) would happen. There would be a planet out there somewhere where random organic molecules in a pond spontaneously joined together to form a perfect copy of Michael Jackson, including all of his memories. There would be a planet populated entirely by clones that look exactly like you. There would be Boltzmann brains that formed spontaneously from clouds of gas in space that are haunted by false memories of having been tortured for hundreds of years on end.

[Halc]

The implications of an infinite universe are pretty startling, actually. When you have an infinite amount of matter and energy with a relatively random distribution throughout space, then every possible scenario will have happened an infinite number of times in the past (so long as the scenario doesn't require longer than the current age of the Universe to occur) and will continue to happen an infinite number of times in the future.

I must disagree. The current state of Earth can have only happened now and not in the past or later. Given an infinite universe (and a couple more assumptions, notably that the universe is in fact everywhere in some state, a premise which I find implausible), then Earth does indeed occur at an infinite number of places, but not at different times since the age of the universe is part of the current state of Earth. There can never be one like it again, because in the future the universe (visible from this hypothetical future Earth) will be in a state of higher entropy than can be measured from this future Earth.

OK, you mention Boltzmann brains, so I suppose a Boltzmann-Earth could exist that would momentarily be in a false state of having just measured a very different universe than the real one out there.

[geordief (OP)]

@Kryptid I see it the other way round.For there to be an identical system to another it has to have identical connections to its environment.

Taken to the extreme that would mean that system A would be a part of an identical universe (including its past ,since the universe is dynamic)  to that of system B.

So system A =system B

[Kryptid]

then Earth does indeed occur at an infinite number of places, but not at different times since the age of the universe is part of the current state of Earth.

I'm not sure I fully understand your reply. Are you saying there is some reason that there cannot be a planet out there somewhere that is identical down to the subatomic level to the way the Earth was 60 million years ago?

@Kryptid I see it the other way round.For there to be an identical system to another it has to have identical connections to its environment.

I'm obviously talking about something being identical to within a particular volume.

[geordief (OP)]

I'm obviously talking about something being identical to within a particular volume

But isolated systems don't exist.

[Halc]

I'm not sure I fully understand your reply. Are you saying there is some reason that there cannot be a planet out there somewhere that is identical down to the subatomic level to the way the Earth was 60 million years ago?

Yes, it can exist, but only 60 million years ago as measured by cosmological time. It can't exist 'now' relative to that coordinate system, and no other <reasonable> coordinate system reaches that far away, but I suppose you could do a custom ad-hoc foliation of spacetime that just asserts that this remote dino-laden Earth happens to be simultaneous with 2021 here.

This again assumes that the universe has a state, unmeasured.

I see it the other way round.For there to be an identical system to another it has to have identical connections to its environment.

There are connections only to the volume's past light cone, so an identical Earth only needs to have identical past with ours, which reaches out at best less than 6 billion LY out. No event in our causal past has ever been further away from 'here' than that, so only the state within that light cone matters, not the whole state of the observable universe, the vast majority of which is not in our current causal past and not even in the causal past of any possible future state of Earth for that matter. It's not what they mean by 'observable universe'.

[Kryptid]

But isolated systems don't exist.

I never said otherwise.

and no other <reasonable> coordinate system reaches that far away

I'm admittedly confused as to why you say this. There is a limited distance for coordination systems?

This again assumes that the universe has a state, unmeasured.

Would not the living things on that hypothetical, far away planet count as doing measurements by making observations? Or are we entering "Wigner's friend" territory?

[Halc]

The triangle ,according to the programme is evidence that  space (spacetime?) is probably flat

Space is flat, not spacetime, as I go into below (bold)

and no other <reasonable> coordinate system reaches that far away

I'm admittedly confused as to why you say this. There is a limited distance for coordination systems?

Inertial coordinate systems, or 'coordinate space' (adjusted for local wiggles for local masses) for instance require (at the largest scales at least) flat Minkowskian spacetime. Space may be flat but spacetime certainly isn't. Such coordinates are subtlety dropped for cosmological coordinates in any situation where the two differ significantly, which is over several billion light years. So for instance, consider visible galaxy X. In cosmological coordinates, the time there is currently 13.8 BY (same as it is anywhere), it is 16.5 BLY away, receding at a rapidity of 1.2c, and the light from that event will never get here because it's somewhat outside the event horizon. Same object in the inertial frame of Earth: The time there is about 8.3 BY. It is about 11.4 BLY away, receding at a velocity of about .83c, and the light from that event should get here in 11.4 billion years, but it won't so that's a contradiction. The coordinate system doesn't work at that scale.

In a theoretical zero-energy solution to the FLRW model, spacetime does become Minkowskian and one can apply inertial coordinates to the entire universe, but the current size then would not be infinite, but rather frame dependent, having a current diameter of 27.6 BLY in in the frame of Earth. A finite size would mean that it indeed has an edge. Anyway, this FLRW solution doesn't match empirical observations.

So that leaves what I called 'ad-hoc' coordinate systems where axes might not be orthogonal and other oddities that prevent the same arithmetic from being used in any direction. One can just assign arbitrary times to all the events of the universe and make the distant dino-laden Earth have the same time coordinate as us.

This again assumes that the universe has a state, unmeasured.

Would not the living things on that hypothetical, far away planet count as doing measurements by making observations? Or are we entering "Wigner's friend" territory?[/quote]
Yes, positing that living things have anything to do with it is the Wigner interpretation, which even Wigner himself abandoned since it was shown that solipsism follows from its premises.

Rovelli showed that no system can measure itself, and thus the cat in the box cannot collapse its own wave function any more that can the poison bottle when it obviously measures the result of the radioactive decay detector. These things are still in a state of superposition relative to anything outside the box, and thus the distant Earth is in superposition of being-there/not-being-there relative to here, as is every event sufficiently distant. Similarly, relative to that distant event which has not measured 'here', Earth doesn't exist since we similarly cannot collapse the wavefunction of 'here' as defined at that distant location. To do so (collapse a wave function outside our past light cone like that) would require faster than light cause/effect. Bell proved this: You can have locality (no FtL cause/effect) or you can have state unmeasured (counterfactuals), but not both.

[Harri]

I have often read about infinite numbers of infinite universes and that there will be another 'me' doing exactly what I am doing now at this exact time. If I am the product of the laws of physics in 'our' universe, and there are an infinite number of universes, could there not be an infinite variety of the laws of physics applying to each universe which could mean there would never be another me?

[Kryptid]

could there not be an infinite variety of the laws of physics applying to each universe

We don't know. Each universe might have the same laws of physics. Or there could be an infinite number of different laws of physics, but with an infinite number of universes having the same laws as each other (and for every possible set of laws).

[Halc]

I have often read about infinite numbers of infinite universes and that there will be another 'me' doing exactly what I am doing now at this exact time. If I am the product of the laws of physics in 'our' universe, and there are an infinite number of universes, could there not be an infinite variety of the laws of physics applying to each universe which could mean there would never be another me?

The point was that our one universe was large enough that there are other copies of you in this universe, never mind any hypothetical other ones. If they're not doing exactly what you're doing now, then they're not exact copies, are they? Depending on your QM interpretation of choice, these might be very (but computably) distant, or quite close, or completely nonexistent.

Are those copies also 'you'? That depends on how you define your identity, something most people don't think about deeply.
Do they 'exist'?  That depends on how you define 'exists'.

[Zer0]

" I Think... therefore I Am! "


Ps - & what about " Some of the other animals that survive without brains include the sea star, sea cucumber, sea lily, sea urchin, sea anemone, sea squirt, sea sponge, coral, and Portuguese Man-O-War. A brain is basically what results when a large group of nerve cells called neurons form one large cluster. "?
(Think about it)
🧠

[Harri]

I know the idea of another 'me' out there in our universe is totally hypothetical and possibly not provable one way or another, ever. But for those who have indicated the possibility of this being the case, have they or do they need to take into consideration what happens to 'me' and our universe before relativity, at the uncertain quantum level?

[Colin2B]

But for those who have indicated the possibility of this being the case, have they or do they need to take into consideration what happens to 'me' and our universe before relativity, at the uncertain quantum level?

Not sure how relativity would come into it, but if you don’t know of their existence then it would be impossible to take into account what happens to them.
As @Halc says, you need to consider what you mean by identity ‘me vs otherme’. This has been explored to some extent in Star Trek and other sifi with respect to the transporter.

[Halc]

I know the idea of another 'me' out there in our universe is totally hypothetical and possibly not provable one way or another

Again: If
A) our universe is spatially infinite
B) You accept that effect can precede cause or that a cause can have effects at faster than light
C) The universe is everywhere in some state at a given time, however unknown or unmeasured

Only then does it logically follow that there must be arrangements of atoms identical to the arrangement of atoms that is you here. All that remains is:
D) do you consider that identical arrangement of atoms to be another 'you' which of course depends on your definition of identity.

I personally accept only premise A) and neither B nor C, and therefore if asked if these copies exist, I'd say no.
It depends significantly on your quantum interpretation of choice. There's a nice chart on wiki: https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics#Comparisons
The 3rd to last column is 'local dynamics' which is green if B) is false.
The 2nd to last column is 'counterfactual' which is green if C) is true. No valid interpretation can list both as green, as proven by Bell.  Only the bottom two interpretations meet the criteria above. Essentially Bohmian mechanics. If that's not your interpretation of choice (it certainly isn't mine), then these 'copies' don't exist.

do they need to take into consideration what happens to 'me'

I don't think this can be answered without a definition of what you consider 'me' to mean.

[alancalverd]

I think the question deserves inverting - often a good starting point for an investigation.

If the universe is finite, either it has a boundary, or we can define a vector r with its origin here and its endpoint outside the universe. So what is outside that boundary?  Why can't we define a vector with magnitude 2r?