[Europa (OP)]

There was space which doesn't contain bread before the experiment, but does contain bread afterward.

True; but the space was not empty before the bread arrived.  What did the bread displace?

There is no known viable model of a bang happening at a location in otherwise empty space.  So the bread expanding into not-bread space analogy just doesn't work.  The bread is the space, and it having an edge would violate the cosmological principle on which all the theories rest.

What is the cosmological principle on which all the theories rest?

[Professor Mega-Mind]

In response to Bill S. ;
There is an argument to be made that the expansion of space is directly and proportionately related to the contraction and compression of most of the universe's mass . This concentration apparently includes a significant amount of the "field" or "substrate" that constitutes space-time itself ; the best analogy being that of a party-balloon being crushed in the middle , and then expanding at the ends .
The above is obviously mass-related and not volume-related , as different epochs of universal evolution have had widely differing rates of material agglomeration and mass-accumulation .
The possibility of significant regional variation definitely exists , and could possibly explain some notable large-scale anomalies , such as "dark-flow" , "great-attractors" , etc .
*Another hidden-balance it is ! .
------------------------------------------
*Read my Post #5 at :
^ quora.com/When-a-photon-is-cosmologically-redshifted-where-does-its-energy-go/ 

[Eternal Student]

Hi  @Professor Mega-Mind

    Thanks for your time but your reply seems to use words without providing useful understanding.  Well that is to say  I can't understand it and I'm not ashamed to admit that.

There is an argument to be made that the expansion of space is directly and proportionately related to the contraction and compression of most of the universe's mass

     A FRW universe does not have to contain any mass.  We can model a universe that is filled with radiation and therefore has no rest mass in it.  Expansion (or contraction) is still present in the model.

This concentration apparently includes a significant amount of the "field" or "substrate" that constitutes space-time itself

    There are quotation marks around "field" and "substrate" which indicate that they are not used in a conventional sense.  I have never seen space-time described as a field.   There are fields defined on space-time but space-time itself is not usually considered as a field.  Therefore this sentence conveys no useful information to me.

[yor_on]

You're correct ES. SpaceTime can't be described as a field. But what should we describe it as?

[Eternal Student]

Hi Yor_on I hope you are well.

    The simplest answer is to describe spacetime as being a mathematical space similar to ℜ⁴.  I'm not sure who is reading this, so I'll explain that this is just a 4-dimensional version of the mathematical representation of space that everyone learned about in school.   
    Thus, in school a point in space was specified as  (1 , 2, 3)  if it was 1 unit along the x-axis, 2 units along the y-axis    etc.    All of space was then the whole collection of points   (x,y,z)  where x,y,z are any real numbers.
    Space-time is just the 4-dimensional version of this.   The term "spacetime" was first used with Newtonian Mechanics and it was just a standard Cartesian product of space co-ordinates and the time co-ordinate.  It really wasn't anything complicated - just a way of specifying points or "events" in a 4-dimensional mathematical space.

    For more elaborate models in Physics, spacetime must have additional mathematical properties.  For example, we may require that spacetime is a vector space with a metric defined on it.  For Special Relativity that metric should be the Lorentzian metric and it is technically only a "pseudo-metric"  (but fine details like this only concern Mathematicians not Physicists and I won't bore anyone with more details).

   For General Relativity, a reasonable definition of spacetime is that it is a differentiable manifold.  The key point is that the spacetime is the domain (the background) on which we can define fields.  To phrase this more simply, it is just a set of points with some mathematical structure and only after we have established this can we sensibly define fields on it.

   "Spacetime" has come to take on many different meanings - but for the Cosmology which is being discussed in this thread, it's enough if spacetime is just a set of points  { (t,x,y,z) }.

Best wishes and bye for now.

[Professor Mega-Mind]

Mr. E-S and Yor-On ,
The application of numerical values to specific interrelations within space-time is a matter of quantification .
As an informed layman , I address these subjects primarily from a qualitative perspective , that is... cause-and-effect/structure/interelations/ characteristics/etc .
Now then , Yor-On made an excellent point above ; "we" really do not know exactly what space-time is made of . We can only be sure that it is not nothing , as that would not allow for any continuity/or contiguous traits/or interdependent relations/or consistent values/or even the enforcement of the Laws-Of-Physics !
Space-time obviously embodies an extremely strong form of universal connectedness , something which allows it to function as a consistent and contiguous entity .
If space-time were nothing , then no energy/mass/interrelation would be able to manifest or interact . In otherwords , the Universe absolutely could not exist !

*Measure it any way you want , my fundamental proposal is logical .

[yor_on]

That should mean that we move SpaceTime as we locally experience it to a mathematical abstraction, doesn't it ES? What I prefer to differ in calling one locality, versus a 'global approach'?.

[yor_on]

And you're right in that Mega, it has to have a 'global connection' to exist practically.  At least I think you're correct in that assumption. We have 'c' as a limiter, locally defined for it. We also have mass relative 'light', bosons and fermions. What defines ones reality is what we experience and can experiment on locally. It's very hard to imagine some 'higher dimension' joining my locality with that global definition. It makes us blind.


rearranging :)

You could express it this way. That the universe behave as it does moves the abstraction to something real.

Although with a caveat. It's not fields, ES is as far as I see perfectly correct in stating that this can't be the case.

[Professor Mega-Mind]

To yor-on ,
So... spacetime is contiguous AND differential , ergo it varies in both a qualitative and quantitative manner .
That speed-limit 'c' is fascinating , seeing as how powerfully integral space-time must be , in order to enforce such a law !
Also , Einstein himself described gravity-waves as "disturbances in the fabric of the Universe" . This of course , directly implies that space-time is a something , not a nothing .
Incidentally , this also explains how e-m radiation can be generated from nothing.

*There must be a joining element or constituent fundamental here , perhaps involving the quantum-universe ..🙂

[yor_on]

As far as I know Mega Einstein did not like any geometrical definition of it. He preferred a mathematical approach. What we can deduce from this universe is that it has to have a sort of logic to it. Otherwise, assuming relativity, it wouldn't exist except possibly locally defined. but to get a global definition we have to use mathematics joining it. The geometrical definition will be local, defined by your measurements.
=

that's the one that hurts my head. A local approach to a SpaceTime not needing this global description. It's a contradiction in terms assuming our commonly agreed on universe to exist using only a local definition. Because it differs between observers. So what we define as a global definition must by necessity become mathematical. But it is also so that we all agree on it existing, and experience much the same. Your clock is locally defined invariant, perfectly measuring your invariant lifespan. And so do mine.

And that is why I think you're correct in your assumption of us needing something to connect our local definitions. But it's not fields.

[Europa (OP)]

I keep hearing the Universe is expanding in comparison to like a balloon inflating, the evidence an apparent red shift observed of matter. We do not observe space red shifting we only observe light/matter interaction red shift, so how from that do you conclude the Universe is expanding when that makes no logical sense or is a any sort of rational thought?
I read this morning that it is now expanding faster than we first thought and soon and the Universe will become cold and the Universe will end, how on Earth doe's any one derive that ?

It it is not possible to expand into nothing
No human knows what the universe is expanding into, if anything.
The universe might actually be contracting not expanding

[Professor Mega-Mind]

To yor-on ,
I am full agreement with your view ; w/o a global "reality" , no common frame-of-reference is possible . Also , no two things would be able to relate to each other .
-----------------------
To Europa ,
Consider that as things gain velocity , they contract . Now suppose that the universe as a whole has gained a very high velocity , in a 4-dimensional sense , being drawn or pushed into the future ever faster . This could cause a type of Lorentz-Contraction , making everything inside of this universe get smaller , relative to the universe itself . If Lorentz-Contraction and Time-Dilation became more pronounced as "velocity" increased ,then time would pass ever slower for the affected contents , leading to the perception that the Universe's expansion was happening ever faster .
*.Badda-boom-badda-bang !
In a wild & crazy yuniverse , it could happen ! .🤯

[Europa (OP)]

To yor-on ,
I am full agreement with your view ; w/o a global "reality" , no common frame-of-reference is possible . Also , no two things would be able to relate to each other .
-----------------------
To Europa ,
Consider that as things gain velocity , they contract . Now suppose that the universe as a whole has gained a very high velocity , in a 4-dimensional sense , being drawn or pushed into the future ever faster . This could cause a type of Lorentz-Contraction , making everything inside of this universe get smaller , relative to the universe itself . If Lorentz-Contraction and Time-Dilation became more pronounced as "velocity" increased ,then time would pass ever slower for the affected contents , leading to the perception that the Universe's expansion was happening ever faster .
*.Badda-boom-badda-bang !
In a wild & crazy yuniverse , it could happen ! .🤯

No one knows that, in fact the universe might actually be contracting back to where it began.  Nothing is known so one theory is as good as the next which is why physicist are now speculating that the universe if fake, nothing more than a simulation

[Professor Mega-Mind]

Yes , but...
By "fake" they mean that there is no real "matter" , only energy in various forms .
In this paradigm , apparently solid objects , from particles to mountains , are composed of "looped" waves of energy . These can become locked together through interactions with various natural forces , thus giving the illusion of solid matter . .

*.To examine this more closely , search up "Photon Pair-Production"
--------------------------------------
Now then , Second-Moon...
IF the Universe is , in a sense , plummeting through higher dimensions at ever-increasing speed , does that not engender the possibility that it might eventually hit bottom ?
In otherwords , is it not possible that the Universe smashes into a giant pile of dead universes , and explodes like an M-80 dropped into an outhouse pit ?
*.Every dynamic system/body in existence produces waste , so doesn't it follow that whoever or whatever made the Universe , did so as a natural function ? .

[Europa (OP)]

Yes , but...
By "fake" they mean that there is no real "matter" , only energy in various forms .
In this paradigm , apparently solid objects , from particles to mountains , are composed of "looped" waves of energy . These can become locked together through interactions with various natural forces , thus giving the illusion of solid matter . .

*.To examine this more closely , search up "Photon Pair-Production"
--------------------------------------
Now then , Second-Moon...
IF the Universe is , in a sense , plummeting through higher dimensions at ever-increasing speed , does that not engender the possibility that it might eventually hit bottom ?
In otherwords , is it not possible that the Universe smashes into a giant pile of dead universes , and explodes like an M-80 dropped into an outhouse pit ?
*.Every dynamic system/body in existence produces waste , so doesn't it follow that whoever or whatever made the Universe , did so as a natural function ? .

Wrong, by fake they literally mean that everything is a simulation and that we and the universe exist on a hard drive

Not my idea but watch if you want a laugh

[Professor Mega-Mind]

Second-Ice-Cube ,
I meant the serious version .
Even Mr.Neil there is laughing up his sleeve ! .😂

[Origin]

Saying the universe is expanding into nothing is misleading.  The problem is the statement implies nothing is something, because you are saying the universe is expanding into...something.
A more accurate statement is 'the universe is expanding'.

[Eternal Student]

Hi.

Now then , Yor-On made an excellent point above ; "we" really do not know exactly what space-time is made of .

    Yes, although that is "spacetime" in the wider sense.  Spacetime does not have to be any sort of substance or thing.  It can be just a co-ordinate system.  There may be real stuff in spacetime but spacetime does not need to be made up from real stuff.
    You can define and imagine "spacetime" in other ways, much as you (Yor_on and Prof. Mega) have done, if you wish.

 - - - - - - -
Europa said the following about expansion and the universe:

No one knows that, in fact the universe might actually be contracting back to where it began.  Nothing is known so one theory is as good as the next which is why physicist are now speculating that the universe if fake, nothing more than a simulation

    It might be contracting but the current evidence and observations suggest that expansion is continuing and actually accelerating.
    "Nothing is known" - maybe -  but that does not imply "one theory is as good as the next".  There are various ways of measuring a theories usefulness.  For example, it has usefulness if we (human beings) can understand it and use it to make predictions.  It does not need to be the absolute truth.  Even if we were in the position of having the absolute truth written down and put in front of us, it won't be useful if we can't understand it and use it to make predictions.  It may be the truth but it will be a poor and useless piece of science.
    "Which is why physicist's are now speculating that the universe is just a simulation":   I don't think that's why they are doing this, or that they (Physicist's) are actually doing this.  The simulation idea has been around for several years now.  It was not started by Neil deGrasse Tyson or any other well-known physicist.  Nick Bostrom, a philosopher from Oxford University, is generally recognised as having started this version of the idea.  If any one group of experts is speculating that the universe is a simulation then it is the Philosophers.  None the less, there is some relevance for Physics and Physicists don't just draw arbitrary lines between their field of study and some other field of study.  There may be some interesting Physics within the idea and Nick Bostrom's original paper did utilize mathematics so it is naturally of some interest to Mathematicians and Physicists.
     To be quite honest, I'm surprised that  Neil dGT is still making youtube videos about this.  It's getting to be quite an old idea now and the videos you keep linking to are really only of "popular" or "surface interest" - but in defence of Neil dGT this is probably what his audience and the producers of the show are asking for.

Best wishes to everyone.

[yor_on]

Well, I look at it as a logic. And that logic leads us to Lorentz transformations when we want to define a 'global universe'. What that means is that we locally defined all have a different definition of it, it's geometry etc. But that we also find things joining it, as laws, symmetries, properties. We expect those to exist everywhere and at all times. If we didn't this universe would become 'magical' to me.
=

Once upon a time I got hooked. On the definition of 'frames of reference' and how it could join us in a same description of the universe geometry etc. I'm still hooked on that one.

[yor_on]

Well ES, you write that the coordinate system used is the 'background' if I get you right. Also that there exist several 'backgrounds' wherefrom we can choose. How about turning it around, the background being a result of your local definition?
=

It's kind of crazy but it connects to this question I have of how we can define a commonly agreed on universe while still defining it as 'observer dependent'. As far as I get it really is observer dependent, the geometry or if you like the manifold change, although maybe not mathematically? I'm not sure about that one. If you are close to light speed measuring on the stars is the manifold mathematically observer dependent? Locally defined.