Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: geordief on 18/10/2021 13:02:08

Title: What if the universe really is infinite?
Post by: geordief on 18/10/2021 13:02:08
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?
Title: Re: What if the universe really is infinite?
Post by: alancalverd on 18/10/2021 13:29:44
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.
Title: Re: What if the universe really is infinite?
Post by: geordief on 18/10/2021 13:47:58
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?
Title: Re: What if the universe really is infinite?
Post by: Halc on 18/10/2021 16:54:58
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'.
Title: Re: What if the universe really is infinite?
Post by: Kryptid on 18/10/2021 20:43:44
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.
Title: Re: What if the universe really is infinite?
Post by: Halc on 18/10/2021 20:55:25
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.
Title: Re: What if the universe really is infinite?
Post by: geordief on 18/10/2021 21:21:29
@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
Title: Re: What if the universe really is infinite?
Post by: Kryptid on 18/10/2021 21:29:22
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.
Title: Re: What if the universe really is infinite?
Post by: geordief on 18/10/2021 21:33:23
I'm obviously talking about something being identical to within a particular volume
But isolated systems don't exist.
Title: Re: What if the universe really is infinite?
Post by: Halc on 18/10/2021 21:53:06
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'.
Title: Re: What if the universe really is infinite?
Post by: Kryptid on 19/10/2021 03:59:13
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?
Title: Re: What if the universe really is infinite?
Post by: Halc on 19/10/2021 13:14:14
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.
Title: Re: What if the universe really is infinite?
Post by: Harri on 19/10/2021 21:43:21
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?
Title: Re: What if the universe really is infinite?
Post by: Kryptid on 19/10/2021 21:48:29
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).
Title: Re: What if the universe really is infinite?
Post by: Halc on 20/10/2021 03:05:32
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'.
Title: Re: What if the universe really is infinite?
Post by: Zer0 on 20/10/2021 08:22:45
" 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)
🧠
Title: Re: What if the universe really is infinite?
Post by: Harri on 20/10/2021 09:59:25
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?
Title: Re: What if the universe really is infinite?
Post by: Colin2B on 20/10/2021 10:11:14
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.
Title: Re: What if the universe really is infinite?
Post by: Halc on 20/10/2021 12:56:43
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.

Quote
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.
Title: Re: What if the universe really is infinite?
Post by: alancalverd on 21/10/2021 00:19:33
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?
Title: Re: What if the universe really is infinite?
Post by: geordief on 21/10/2021 00:35:36
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?
Reminds me of the ending to The Truman Show where the intrepid hero comes to the end of the world and discovers it is made of  billboard paper.

Also reminds me of the crock of gold at the end of the rainbow

I feel  I can live with an infite  universe , but I wouldn't bet the house on it :-) :)
Title: Re: What if the universe really is infinite?
Post by: Halc on 21/10/2021 00:47:25
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.
Those sound like the same option. The boundary is when the vector changes to being outside.
No, the 2nd option is that a vector r with its origin here has its endpoint also here.
This is true of the surface of Earth (positive curvature, finite area, no boundary). It is also true of a torrid surface (like the Asteroids video game, no curvature, finite area, no boundary). In such cases, any vector comes back to someplace it's been before.

Quote
So what is outside that boundary?  Why can't we define a vector with magnitude 2r?
The Milne universe is sort of like that. Everywhere isotropic, and yet finite/bounded with 'nothing' beyond. The vector can be defined (you can give coordinates to locations outside), but you can't go there because no event outside the universe is in the future light cone of any event inside it.
Title: Re: What if the universe really is infinite?
Post by: alancalverd on 21/10/2021 11:47:34
The Milne universe is sort of like that. Everywhere isotropic, and yet finite/bounded with 'nothing' beyond.
This surely defines the observable universe, not the universe, which must include everything (or all the nothing) "beyond".
Title: Re: What if the universe really is infinite?
Post by: alancalverd on 21/10/2021 11:53:57
Those sound like the same option. The boundary is when the vector changes to being outside.
Not so mathematically. An unbounded set (cats) does not include objects that are not members of that set (dogs), but we can define a vector (quadrupeds) in terms of the parameters of that set, which can be extended beyond all possible members of the set (other quadrupeds, all dead cats....).
Title: Re: What if the universe really is infinite?
Post by: Harri on 21/10/2021 22:46:37
Does the big bang theory cause a problem for the infinitely expanding universe theory? Our universe is currently expanding and my understanding is that a reduction of that expansion would bring us to the big bang. But wouldn't that mean that the reduction would also have to be infinite?
Title: Re: What if the universe really is infinite?
Post by: geordief on 21/10/2021 22:59:58
Does the big bang theory cause a problem for the infinitely expanding universe theory? Our universe is currently expanding and my understanding is that a reduction of that expansion would bring us to the big bang. But wouldn't that mean that the reduction would also have to be infinite?
(think my head just expanded :)  )

Well could you have it so that some of the universe did fall back on itself but some was just too far distant and "out of reach" so that it  continued its expansion "to infinity and beyond" :)  ?
Title: Re: What if the universe really is infinite?
Post by: Halc on 21/10/2021 23:05:54
Does the big bang theory cause a problem for the infinitely expanding universe theory?
The big bang theory is the infinitely expanding universe theory

Quote
Our universe is currently expanding
Careful. The space in our universe is expanding over time. 'The universe' is typically defined as all of (or sometimes the visible portion of) spacetime, and spacetime doesn't expand or otherwise change, so while wording it that way is common in pop articles, it is technically wrong.

Quote
my understanding is that a reduction of that expansion would bring us to the big bang.
That would be a big crunch, a sort of different thing that the big bang in reverse since the entropy would be so much higher. Our expansion doesn't look like it will ever slow let along reverse, so no crunch is anticipated.

Quote
But wouldn't that mean that the reduction would also have to be infinite?
The expansion isn't infinite, so neither need be the reduction. The expansion is currently at a non-infinite rate of 70 km/sec/mpc and might eventually settle on an exponential rate of around 57.  The size of space is posited as infinite, but you can expand that or reduce it by any finite figure and it's still infinite. Expansion/reduction works just the same (same finite measured rate) regardless of whether the size of space is finite or not.
Title: Re: What if the universe really is infinite?
Post by: Halc on 21/10/2021 23:07:05
Well could you have it so that some of the universe did fall back on itself
That's one way to describe a black hole. All very crunchy.
Title: Re: What if the universe really is infinite?
Post by: geordief on 22/10/2021 12:31:18
Well could you have it so that some of the universe did fall back on itself
That's one way to describe a black hole. All very crunchy.
Wasn't expecting that. Do the models of the BH and any possible Big Crunch differ in other respects?
Title: Re: What if the universe really is infinite?
Post by: Halc on 22/10/2021 16:08:22
Do the models of the BH and any possible Big Crunch differ in other respects?
In both cases, time ends abruptly for a given worldline, just as it starts abruptly at the big bang.

The big crunch is not a black hole in that matter is still evenly distributed everywhere over infinite space.
I'm not sure if light is still prevent from reaching null-infinity in the crunch scenario. It seems to depend if there's something like anti-inflation at the end. I'd be guessing if I posted an opinion on that.
Title: Re: What if the universe really is infinite?
Post by: yor_on on 28/10/2021 21:19:04
I think I will agree with you Kryptid, although also presuming a 'infinite time' for it. Depending on permutations, assuming that there are only so many ways to arrange them. Atoms, electrons whatever.


syntax
=

Thinking some more of it, I don't need that infinite time, do I? It should be enough with a combination of restricted permutations in a infinite universe for it to be possible. Thermodynamics assume a heat death so with that everything has a end of sorts. But in between, in a universe without end everything (inside those permutations) should be possible. Locally defined at least :) If we add observer dependencies it becomes really tricky.

Although, quantum physically not even a heat death stops those random processes as I understand.
And damn, if that is correct 'time' must exist, even in a heat death of a universe.

I should have realized this sooner. Both Relativity and quantum mechanics agree on this. And it's a shot across the bow for the idea of equalizing thermodynamics to the arrow of time, isn't it?
Title: Re: What if the universe really is infinite?
Post by: yor_on on 28/10/2021 21:22:05
And yes, the universe is weird but no weirder than the assumption of it being some sort of ball containing everything. Once you made that presumption the next question becomes

What's outside it?
Title: Re: What if the universe really is infinite?
Post by: alancalverd on 28/10/2021 23:06:10
The implications of an infinite universe are pretty startling, actually. When you have an infinite amount of matter and energy.......

But a finite amount of stuff expanding into an infinite void is not at all difficult to visualise. Just think of any explosion in a space movie, on a really big scale.
Title: Re: What if the universe really is infinite?
Post by: yor_on on 29/10/2021 06:39:31
What physics refers to as 'densities', isn't it Alan? :)
Funny word that.
Title: Re: What if the universe really is infinite?
Post by: Zer0 on 30/10/2021 00:11:43
Perhaps Fancy Science Magazines are responsible for this logical contradiction.

The Universe, They say...was once packed into a small impeccable point...then grew from a mustard seed to a football in a flash...then inflation from football to earth size...n then kept expanding Forever!

Ps - So then...it's quite possible to pack an Infinity of mangoes into a Finite picnic basket.
🍊
(I cannot see the Earth as a whole one planet until i go into space, and the Earth has no edges...hence the Earth must be Infinite.)
Title: Re: What if the universe really is infinite?
Post by: yor_on on 08/11/2021 19:29:12
Did you know that you have neurons in your stomach Zero? Communicating with your brain :)

There is nothing stating that a 'brain' must be centralized, it may be easier that way but it depends on evolution I think. And I seem to remember that sea stars have neurons too?

https://www.ted.com/talks/heribert_watzke_the_brain_in_your_gut
=

so talking about having a 'gut feeling' may not be that much off the mark.
Title: Re: What if the universe really is infinite?
Post by: Zer0 on 08/11/2021 19:42:45
Did you know that you have neurons in your stomach Zero? Communicating with your brain :)

There is nothing stating that a 'brain' must be centralized, it may be easier that way but it depends on evolution I think. And I seem to remember that sea stars have neurons too?

https://www.ted.com/talks/heribert_watzke_the_brain_in_your_gut
=

so talking about having a 'gut feeling' may not be that much off the mark.

What are you even on about?
🤔
I am unable to make a sensible connection with what i said, & what your responded with.
🙏
I'm not asking you to elaborate, maybe im simply Not at your level hence even if you explained, i still might not get it.
Title: Re: What if the universe really is infinite?
Post by: yor_on on 09/11/2021 11:52:01
Sorry zero, looking at it again I don't see what I reacted on here? Probably me placing it in the wrong thread? It was a comment by you about brains, as far as I remember?
Title: Re: What if the universe really is infinite?
Post by: Zer0 on 09/11/2021 18:08:56
Sorry zero, looking at it again I don't see what I reacted on here? Probably me placing it in the wrong thread? It was a comment by you about brains, as far as I remember?

Section - Physics, Astronomy & Cosmology.

https://www.thenakedscientists.com/forum/index.php?topic=83391.msg658496#msg658496

You are Spot On Buddy!
👍
I dug it up n found it.
(Reply #15)

Very Nicely Done!
& Yes l, what you say resonates & makes sense to me.

Ps - i Apologize i could not relate to it before.
🙏
Now i truly understand what it means when people say, " i have a gut feeling about this "...thinking/guessing/memory is not just in the domain of the brain alone.
(No wonder heart transplant patients report a change of taste or pick up a new habit)
💓
Title: Re: What if the universe really is infinite?
Post by: JohnPi on 27/11/2021 21:46:52
IMHO, universe is just a circle. It may seem that every time you reach its edge it is the universe's end, but it's actually not. Of course many common space facts won't let u believe it, but how we can be sure about fact that universe is not infinite if we have never reached its end, and would we?
Title: Re: What if the universe really is infinite?
Post by: yor_on on 01/12/2021 12:27:58
Thanks for looking it up Zero, so it wasn't just me imagining it. One never knows when senility may hit, every day becoming a first one. Driving by the seat of my pants as it might be seen :)

And yes JohnPi. that's how some theorists imagine it. As a sort of 'dimensional circle'. You can also use time for it, as time dilation should make any recognition of a 'origin' very questionable if one now expect oneself to return, well, depending on scale and lifespans etc.

but it doesn't answer what's 'outside it', and introducing that question will lead you to an even bigger headache than a 'infinite universe'.
Title: Re: What if the universe really is infinite?
Post by: yor_on on 01/12/2021 12:30:21
It could be that the answer to those two is the same. There is nothing outside it and the universe is infinite, as far as we are concerned.