How can space be both infinite and a vacuum at the same time?

Henning said:
The 'edge' of the universe is the speed of light, that's where time ends, and therefor matter and space since matter and space require time to exist.
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What does "time ends" mean?

I've certainly seen weird claims like that in the pop sci literature, but never in anything serious.

The speed of light is not a distance. Not even in the Hubble Law. Redshifts well above 1 have been observed, so the Hubble Law is obviously not linear forever (neither is it expected to be in any cosmology -- there is a derivation of it in my dissertation and in several other places like Ned Wright's cosmology web page).

It's a phrase without meaning or physical consequence.

If it has no consequence, it doesn't exist.
 
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MAKG1 said:
...There is no edge...
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Not only that, but as I understand it, there is no "is." Under the theory of relativity, we can't know the shape of the universe at the present time, because there is no simultaneity at a distance. "The present" is thus undefined at a distance, because it differs for different observers.
 
When I was a kid I started thinking about the following thing and it bothered me greatly that I couldn't wrap my mind around it or in any way understand it.

Imagine you had a spaceship and you were able to take it right up to the very edge of the universe. Then you accelerate forward. What happens?
 
cowman said:
When I was a kid I started thinking about the following thing and it bothered me greatly that I couldn't wrap my mind around it or in any way understand it.

Imagine you had a spaceship and you were able to take it right up to the very edge of the universe. Then you accelerate forward. What happens?
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What makes you think there is an edge?
 
MAKG1 said:
What does "time ends" mean?

I've certainly seen weird claims like that in the pop sci literature, but never in anything serious.

The speed of light is not a distance. Not even in the Hubble Law. Redshifts well above 1 have been observed, so the Hubble Law is obviously not linear forever (neither is it expected to be in any cosmology -- there is a derivation of it in my dissertation and in several other places like Ned Wright's cosmology web page).

It's a phrase without meaning or physical consequence.

If it has no consequence, it doesn't exist.
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Time only exists within space time, space time is what defines our universe as we can perceive it. There are more dimensions to our universe than just space time, think of a confluence of dimensions like a Venn Diagram. Quantum physics gives us both the quantum leap, instantaneous shifts of subatomic particles in space as well as quantum entanglements to show that there can be instantaneous transfers of both matter and information. The hardest thing there is for the human mind to comprehend is timelessness, however it has been known since the writing of the Torah, "I am the Alpha and Omega".
 
I like to (non-scientifically) theorize that gravity is not an attractive force, but repellant force, and the only reason it seems to be attractive is because the Earth (or other body) creates a "shadow." And with it being a repelling force, and the idea that the furthest reaches of the universe are expanding faster than the not so distant reaches there's nothing beyond the "edge" to push back.

I also think the reason that 90%(?) of the mass of the universe is dark matter, is because the universe is 9 additional dimensions like the one we are currently, but we can't detect with conventional means.
 
cowman said:
Imagine you had a spaceship and you were able to take it right up to the very edge of the universe. Then you accelerate forward. What happens?
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You fall off the edge of the universe...the ancients had it right, they just had the wrong edge...
 
cowman said:
When I was a kid I started thinking about the following thing and it bothered me greatly that I couldn't wrap my mind around it or in any way understand it.

Imagine you had a spaceship and you were able to take it right up to the very edge of the universe. Then you accelerate forward. What happens?
Click to expand...


That is how I came up with my Pac Man theory.
You show up on the inside of the opposite edge.
 
48dodge said:
Vacuum is simply the absence of pressure much like cold is the absence of heat.
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I vaguely remember being told in a physics class that there is no 'cold' and there is no 'heat'. Heat is simply a measurement of the amount of energy being radiated by a system.

Henning said:
The hardest thing there is for the human mind to comprehend is timelessness
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The entire concept of infinite anything is difficult for the human mind to comprehend.

For most, it's easier to look at what we have here and believe we are kings of our own little world than contemplate the fact that we are miniscule and insignificant outside of our tiny planet.
 
MAKG1 said:
At the speed of light?

No. The universe is known to be expanding, and the rate was measured long ago. More recently with some precision. It's proportional to distance from the observer (for redshifts well below 1), with a value of about 68 km/s/Mpc.
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We don't know if there is something at the edges of the Universe creating reverberation of the particles that have (finally) made it there, since we're at the centerpoint.
 
MAKG1 said:
Well, the speed of light is known not to change or molecular hydrogen hyperfine emission lines in distant galaxies would be spaced differently than nearby, and they aren't. They are easily observed with radio telescopes at a wavelength of 21 cm.
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It has been observed and measured that the speed of light changes while travelling through water.
 
Fredbob711 said:
I vaguely remember being told in a physics class that there is no 'cold' and there is no 'heat'. Heat is simply a measurement of the amount of energy being radiated by a system.



The entire concept of infinite anything is difficult for the human mind to comprehend.

For most, it's easier to look at what we have here and believe we are kings of our own little world than contemplate the fact that we are miniscule and insignificant outside of our tiny planet.
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We are not only minuscule and insignificant outside our tiny planet, we are minuscule and insignificant on it at this point. We will not become significant until we start doing the right thing. The choice of significance is one we make, or rather refuse to make.
 
Don't weigh airplanes because they gain weight at the speed of light influenced by the time and vacuum of space?

 
Jaybird180 said:
It has been observed and measured that the speed of light changes while travelling through water.
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The speed of light in a medium is not relevant to an argument that distances have changed with time.

Nor is there a relevant observation of HI hyperfine emission from within liquid water.
 
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bnt83 said:
Don't weigh airplanes because they gain weight at the speed of light influenced by the time and vacuum of space?

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:rofl::rofl::rofl:

I'm taking that as sarcasm. I find it funny that people would rather not have accurate data to give them plausible deniability in case they have an accident due to being out of weight and balance. Better to have accurate data IMO, plausible deniability won't save your life.
 
Henning said:
Time only exists within space time, space time is what defines our universe as we can perceive it. There are more dimensions to our universe than just space time, think of a confluence of dimensions like a Venn Diagram. Quantum physics gives us both the quantum leap, instantaneous shifts of subatomic particles in space as well as quantum entanglements to show that there can be instantaneous transfers of both matter and information. The hardest thing there is for the human mind to comprehend is timelessness, however it has been known since the writing of the Torah, "I am the Alpha and Omega".
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Henning, that argument is circular.

The universe doesn't look like a Venn diagram. It doesn't expand "into" anything. It has no center and no direction and no edge. And you can derive the expansion from just that, a few parameters (all of which are well measured now, mostly from microwave background measurements), and Newtonian dynamics. You don't even need general Relativity, but if you use it, you get the same answer.

You can easily measure curvature without any reference to an outside, by trying to draw parallel lines or closed polygons. And that's the approach GR takes.

If you make an edge of the universe, you no longer have isotropy or homogeneity. You can be near the edge. In fact, most of the volume of the universe is near the edge, so you have to explain why we appear to be in the center if you want to make a model like that. The conventional explanation is that in a uniform infinite expansion, every place is the center.

And that Alpha and Omega thing is in Revelation, not the Torah. The Torah is too old for greek letters to be discussed; none of it was written in Greek.
 
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If it's not expanding how is everything* moving away from us?

* - yes, I know within our local group there is the Great Attractor
 
EdFred said:
If it's not expanding how is everything* moving away from us?

* - yes, I know within our local group there is the Great Attractor
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It is expanding. It's just not expanding into anything. Well, more precisely, adding an embedding space to the universe has no consequence, and is therefore completely untestable.

The universe isn't an inflating balloon, nor is it a bomb. The best (still rather limited) analogy is infinite rising bread.

The Great Attractor is not in the local group. It's in the (much larger) local supercluster in the direction of Virgo. The local group essentially has two large galaxies and a few dozen smaller ones.
 
MAKG1 said:
It is expanding. It's just not expanding into anything. Well, more precisely, adding an embedding space to the universe has no consequence, and is therefore completely untestable.

The universe isn't an inflating balloon, nor is it a bomb. The best (still rather limited) analogy is infinite rising bread.

The Great Attractor is not in the local group. It's in the (much larger) local supercluster in the direction of Virgo. The local group essentially has two large galaxies and a few dozen smaller ones.
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If expanding, it's getting bigger, ergo it is taking up more space. It has to be taking up space "somewhere." And how can one unequivocally say, "there is nothing beyond 'the edge'" No one can know that, and to state it as fact.

And yes I meant supercluster, I was multitasking.
 
EdFred said:
It has to be taking up space "somewhere." And how can one unequivocally say, "there is nothing beyond 'the edge'"
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You're assuming space is conserved. It is not. Nothing in GR requires it. A rather deep theorem (Noether's) would tie it to some symmetry if it were conserved. Unlike energy and momentum (which are related to time and space symmetries, respectively), there is no corresponding symmetry to space conservation. But there has to be if it exists.

Saying "there is nothing beyond the edge" and "there is no edge" are very different statements. There is no evidence whatsoever that there is an edge, and you can define a completely coherent and much simpler model of the universe that has no edge.

There is evidence against an edge in the fact that it has never been observed, and most of the volume should be near the edge, if it existed.

The earth has no edge as well; this is familiar. You can drive/boat/fly/whatever in any direction forever and never fall off. It also has finite surface area. The universe might have been built that way, but it's ruled out by distant supernovae observations.
 
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MAKG1 said:
You're assuming space is conserved. It is not. Nothing in GR requires it. A rather deep theorem (Noether's) would tie it to some symmetry if it were conserved. Unlike energy and momentum (which are related to time and space symmetries, respectively), there is no corresponding symmetry to space conservation. But there has to be if it exists.

Saying "there is nothing beyond the edge" and "there is no edge" are very different statements. There is no evidence whatsoever that there is an edge, and you can define a completely coherent and much simpler model of the universe that has no edge.

There is evidence against an edge in the fact that it has never been observed, and most of the volume should be near the edge, if it existed.

The earth has no edge as well; this is familiar. You can drive/boat/fly/whatever in any direction forever and never fall off. It also has finite surface area. The universe might have been built that way, but it's ruled out by distant supernovae observations.
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We're told the universe was once a singularity. It's gotten bigger since then. There is definitely a boundary to the universe. And it's taking up more space than it was x-billion years ago.
 
For those genuinely curious and able to invest the time...

ITunesU has a Yale University course titled "Astronomy - Frontiers and Controversies".

Quite comprehensive. I was lost on much of the math, but still got a lot out if it.
 
We're told the universe started as a singularity, then inflation caused it to expand for some unknown reason, then stop for some unknown reason, there is dark matter that makes up 90% of universe but we can't find it, there is dark energy that we don't know anything about, all this happen once 16 billion years ago....
What kind of drugs do you need to be on to be an astrophysicist?
 
EdFred said:
We're told the universe was once a singularity. It's gotten bigger since then. There is definitely a boundary to the universe. And it's taking up more space than it was x-billion years ago.
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I think you're in the same conceptual hang up that we all get. If the universe is everything that exists, there doesn't need to be anything outside of the universe. It is not a requirement that the universe be expanding into something or some space. Indeed, a concept of outside the universe may not even make sense.

I struggle with the concept too.
 
I get the concept. What I don't get is the absolute statement that the universe absolutely positively isn't part of a superverse. We might be that rising bread in a super bakery.
 
EdFred said:
I get the concept. What I don't get is the absolute statement that the universe absolutely positively isn't part of a superverse. We might be that rising bread in a super bakery.
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"It's taking up more space" doesn't seem to gel with the concept, because it presupposes that the universe is expanding into some space beyond it.
 
It does if it is part of something bigger.
 
If God is reading this thread, She's probably laughing Her ass off!
 
I thought the universe was everything.
It sounds like most think of it is a subset of everything
 
EdFred said:
We're told the universe was once a singularity. It's gotten bigger since then. There is definitely a boundary to the universe. And it's taking up more space than it was x-billion years ago.
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Singularity does not imply zero diameter. It means infinite density. You can still have infinite extent with infinite density. Infinity is not a number, and it's incorrect to think of it as 1/0, though that's the way most of us made infinite numbers in high school. 1/0 is not invertible. As an example, if you consider the limit as x -> 0 of 1/x, you can always invert it, but whether x is positive or negative, you get a different inverse. If it's complex, you get even more fun stuff.

So, the "definitely" doesn't work. There is no evidence whatsoever for a boundary to the universe.

Most scientists don't believe there really was a singularity anyway, as quantum effects probably start to get in the way below the Planck scale. While the Planck scale is really, really, really small, it's not zero. There could be a singularity; that part is not terribly well understood, as it's not possible to probe down to that scale yet (and it's gonna be a lllloooonnnnngggg while before that changes).

The "observable" universe was once very tiny, but that is not the universe. It's actually not nearly as useful a concept as you might think, and you need scales larger than that to explain the microwave background.

A "closed" universe takes up the same (finite) volume for all time. Our universe is known not to be closed, so it's volume is infinite.
 
EdFred said:
I get the concept. What I don't get is the absolute statement that the universe absolutely positively isn't part of a superverse. We might be that rising bread in a super bakery.
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No one made that statement.

My statement was that there was no evidence whatsoever for that.

Some folks have speculated on it, particularly Andrey Linde, but it's not science, it's speculation. There is no evidence, and it is not testable.

But that "super verse" (Linde actually calls it the multiverse) is not something the universe is expanding into, and the universe still doesn't have an edge. It's an interesting concept involving the occasional quantum fluctuation that produces a new "normal" universe while most of the universe is in an exponentially inflating space. That is, the stuff far outside our horizon is expanding much faster than our simple t^(2/3), so every part of it gets further from us faster than the horizon grows. A lot faster.

I don't buy it; it's cute, but not unique and not testable in any way, which makes it metaphysics rather than physics. But it's out there and can be an interesting read. Despite not being a native English speaker (he's a former Soviet, one of quite a number of emigres who came in the early 90s), Linde's writing is surprisingly good. It is self consistent, but it's not unique in that regard.
 
Palmpilot said:
If God is reading this thread, She's probably laughing Her ass off!
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Hehe! good one.

I wonder if she sent Feynman a message; "hey - you wanna good laugh? check out the space vacuum thread on POA. lol".

I'm sure he would appreciate it.
 
I am really trying to keep up.
My brain cannot grasp a lot of the real thinking much beyond my little epiphany
I may have to go back to d!ck and fart jokes.
 
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