Question What are we expanding into?

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Catastrophe

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In such an environment, I always remember that <5% is "ours" and the other >95% is dark energy and dark matter. Perhaps you could fill your "nothing" with some of these?

Cat :)
 
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Catastrophe

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Or if you like linear expansion:

Is Minkowski spacetime a solution of the Friedmann Equations? (1 Viewer)

timmdeeg
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The empty FRW-universe with curvature parameter k=−1 and expanding linearly is well known. Also that it is mathematically equivalent (after a coordinate transformation) with the Milne universe which also expands linearly.

I wonder if the Friedmann Equations have another solution (I remember something like that, but perhaps wrongly): The static Minkowski spacetime. If true this seems to require H=0 and k=0 and thus ρ/ρc=1. However this doesn't seem to make sense because in the empty universe the densities are zero and thus k has no defined value.

Any help appreciated.

The mind doesn't create the truth - but rather stumbles across it
- Aurelius Augustinus -

From: Cosmology Forum My emphasis.


Cat :)
 
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The empty FRW-universe with curvature parameter k=−1 and expanding linearly is well known. Also that it is mathematically equivalent (after a coordinate transformation) with the Milne universe which also expands linearly.
I'm not someone who has even tried to study GR, but from what I have gathered over time...

Originally, Friedmann demonstrated that gravity in GR would either expand or contract the universe based on his math. His work given to Einstein was on a mathematical level not a physics approach (suggesting a real expansion or contraction). Einstein later recognized Friedmann's, and Lemaitre's, work. [Lemaitre, however, took his work beyond math and into physics; he calculated the first attempt at an expansion rate using Slipher's redshifts.]

Einstein recognized, but inadequately, that his model had no expansion but that some pushing force within spacetime itself must exist to keep it from collapsing, hence his light-duty cosmological term, that proved way too short for modern observations with acceleration.

... in the empty universe the densities are zero and thus k has no defined value.
Yes, and deSitter discovered that redshifts would exist in his Static universe but....with no matter!. :) I'm sure he was just simplifying GR to get on a path to a better model. But he was able to show that a static universe could have increasing redshifts with distance in a static universe. Einstein's own model was fine with matter but he could not figure out how redshifts would work in what all knew was the actual universe - a static one. Lemaitre solved both their problems with expansion.

I do know that Hubble had worked with deSitter at IAU events in Europe and Hubble, no doubt, respected de Sitter. So, IMO, since redshifts could be shown within GR, by the great deSitter, then perhaps redshifts were not a result of expansion. He chose to letter theorists duke it out and he not once argued that the universe is expanding. He did produce, with Humason, the best known data giving the correlation of redshift and distance, hence people just connected the two big dots and assumed he was demonstrating an expansion rate, which, again, he never did.
 

Catastrophe

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My thought here:
"In such an environment, I always remember that <5% is "ours" and the other >95% is dark energy and dark matter. Perhaps you could fill your "nothing" with some of these?
was that, since we are aware of "absence of matter" only within the <5% have we any justification to assert that that same "nothing" is applicable to the other >95%? Do we know that our "nothing" is not simply brought about by dark whatever, taking up the space vacated by mass?

Cat :)
 
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Do we know that our "nothing" is not simply brought about by dark whatever, taking up the space vacated by mass?
This opens a whole host of interesting questions one may ask, but if your point is that dark matter and/or energy could explain "nothing" then this is theoretically impossible.

Isn't the effect of dark energy supposed to be visible in observable space?, that is the expansion of the universe.
 

Catastrophe

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This opens a whole host of interesting questions one may ask, but if your point is that dark matter and/or energy could explain "nothing" then this is theoretically impossible.

Isn't the effect of dark energy supposed to be visible in observable space?, that is the expansion of the universe.
I take your point. Perhaps I had in mind the possibility of something still unknown, its purpose' to abhor a vacuum. Not at all scientific - a philosophical flight into fancy for which I apologise to anyone taking it too seriously. :) :) :)
 
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Perhaps I had in mind the possibility of something still unknown, its purpose' to abhor a vacuum.
No actually this is really interesting because I never considered dark energy, vacuum or pressure for these kinds of questions.

A vacuum, dark energy, dark matter, nothing etc. may have something in common or related, I think I'll read more about this stuff only for the purpose to understand more.
 

Catastrophe

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No actually this is really interesting because I never considered dark energy, vacuum or pressure for these kinds of questions.

A vacuum, dark energy, dark matter, nothing etc. may have something in common or related, I think I'll read more about this stuff only for the purpose to understand more.
Sorry I can't refer to anything. It just came out of my philosophically flighty senile left hemisphere. If you find anything, I'd be grateful if you would inform me :) :) :)

P.S If it helps, it was shortly after I wrote post #8 in "What intrigues you about space".
 
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The belief that nothing exists outside "our" universe is akin to believing the world is flat. We have such a limited view of space, time and matter, making every thing fit into a very small space. What are we turning into? We as a species or we as this universe? Is the universe expanding, or are the tentacles that make up the spiral arms coagulating? The distance between the spiral arms create greater distances leaving a even greater void between galactic arms. We may not be able to traverse the space between arms, but can travel down the corridors that make each galactic tentacle which may stretch from the galactic core to the outer rim of the universe. Once at the outer rim of the universe we shall find infinity where an infinite number of independent universes exists. Time has no beginning, and time will have no end. As galaxies merger into larger one, so shall universes have and do merge. Did this universe begin with a bang, or did it begin with a merger of a smaller universe? Are there such things as Universal Clusters? Are there such things as Dwarf Universes? Are we now in the process of merging with yet another universe? Are we alone in the cosmic realm of space, or just a thread in the fabric of life? Time, space and matter are infinite, this universe is finite.
 

IG2007

"Don't criticize what you can't understand..."
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The belief that nothing exists outside "our" universe is akin to believing the world is flat. We have such a limited view of space, time and matter, making every thing fit into a very small space. What are we turning into? We as a species or we as this universe? Is the universe expanding, or are the tentacles that make up the spiral arms coagulating? The distance between the spiral arms create greater distances leaving a even greater void between galactic arms. We may not be able to traverse the space between arms, but can travel down the corridors that make each galactic tentacle which may stretch from the galactic core to the outer rim of the universe. Once at the outer rim of the universe we shall find infinity where an infinite number of independent universes exists. Time has no beginning, and time will have no end. As galaxies merger into larger one, so shall universes have and do merge. Did this universe begin with a bang, or did it begin with a merger of a smaller universe? Are there such things as Universal Clusters? Are there such things as Dwarf Universes? Are we now in the process of merging with yet another universe? Are we alone in the cosmic realm of space, or just a thread in the fabric of life? Time, space and matter are infinite, this universe is finite.
That is more of a Philosopher's approach than a Physicist's approach. But, I respect that. :)

According to the Big Bang Theory, the Universe is everything that exists. The word "Universe" comes from the Latin word "Universus" or "Universum," which literally means everything combined into one single whole. Now, if we consider the Universe to be something that is everything-that-exists and infinite, we get that there is no question of the Universe having an edge or having a centre, because something like that cannot exist. So, there is no question of an expansion or reduction, because infinity plus anything is infinity. But, if we consider the universe to be everything-that-exists and finite, we get that there is indeed a so-called "edge" of the universe and also a centre, but due to the way of expansion that happens in our Universe, it is impossible to find it. I can literally call myself the centre of the Universe and I won't even be lying! ( ;) ) Now, if you strictly adhere to the Big Bang Theory, there is no question of the Universe or time or space or matter or energy, being infinite, because... well, I guess I have again misplaced the sentences. ;)

But now, you might say, Science believes nothing but proof, what proof do I have that the Universe has nothing outside it? Well, nothing. And so do you, if you say that the Universe has infinity outside it. Now, as we are without proof, and Science ends here. I guess, I also have to take the help of Philosophy here. I have never beheld or heard or felt or tasted or smelled infinity. And nor has any human ever. I am about to make a parody of an old quote, "Nature abhors infinity." :)
 
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Catastrophe

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k276

If I may please help you a little:

Quote
The belief that nothing exists outside "our" universe is akin to believing the world is flat. . . . . . . . . . . . . . . . . . . . . . . . . Is the universe expanding, or are the tentacles that make up the spiral arms coagulating?
Quote

As IG has correctly pointed out, the Universe (the only one Universe) is, by definition, all there is.
As far as the tentacles are concerned, you seem to be mixing up galaxies with the Universe. There are billions of galaxies in the Universe, and billions of stars in a galaxy

I can highly recommend this as a reliable readable introduction:

Insights Intro to Big Bang and Infinity Concepts - Comments Last Post Nov 2, 2020 3 Replies 50 Views 5K

Source https://www.physicsforums.com/forums/cosmology.69/.

Cat :)
 
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Catastrophe

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IG, you ask: "what proof do I have that the Universe has nothing outside it? "

I would suggest that proof is not an issue. If, as you eloquently explain, Universe is totality, then the definition alone "does the job".
 
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IG2007

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IG, you ask: "what proof do I have that the Universe has nothing outside it? "

I would suggest that proof is not an issue. If, as you eloquently explain, Universe is totality, then the definition alone "does the job".
That's a good point, if the Universe is totality, there is nothing outside it. Thanks for that, Cat :)
 
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Catastrophe

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"We are expanding into nowhere". This is ambiguous (unfortunately).

1. not in or to any place; not anywhere.
In context, not anywhere, no place to expand into, .would mean nowhere outside the Universe, confirming the idea that the Universe is all there is

2. no place. "there was nowhere for her to sit"This sort of overlaps with 1. but can also mean (as in example), there is somewhere but it is occupied - this does not really translate into the Universe context.

Cat :)
 
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IG2007

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"We are expanding into nowhere". This is ambiguous (unfortunately).

1. not in or to any place; not anywhere.
In context, not anywhere, no place to expand into, .would mean nowhere outside the Universe, confirming the idea that the Universe is all there is

2. no place. "there was nowhere for her to sit"This sort of overlaps with 1. but can also mean (as in example), there is somewhere but it is occupied - this does not really translate into the Universe context.

Cat :)
Sorry, wrong word, we are expanding into "nothing." :)
 

Catastrophe

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IG, this is getting into semantic difficulties, isn't it? Are you not including space as part of the Universe?
Also "something devoid of space" surely be non-existant, and therefore cannot be expanded into?

Cat :)
 
Jun 1, 2020
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Actually, the Universe is not expanding, it is the space that is. So, a better one would be "space is expanding into something devoid of space."
Yes, and we, and our sister galaxies, are "floating" in space, so we see the results of what is truly expanding. And, the galaxies themselves aren't expanding since their local gravity is far stronger than the juice behind the expansion.
 

IG2007

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IG, this is getting into semantic difficulties, isn't it? Are you not including space as part of the Universe?
Also "something devoid of space" surely be non-existant, and therefore cannot be expanded into?

Cat :)
It's indeed hard to semantically describe something that doen't exist. Isn't it? :)

I guess, I am still semantically correct. Imagine the way we breathe, when our lungs are devoid of oxygen, oxygen gets into it because of the process of diffusion. In the same way, something that does not exist, has "no thing" and nor space, and thus space tries to fill it up. I guess I am happy with that analogy. I would love to hear comments on that.
 

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