Space is not infinite.

[michel123456]

According to the Big Bang theory there is no center or other fixed location inside the Universe that space is expanding from, space expands equally everywhere.

 

That is the reason why I dislike animations with balloon analogies like the one posted by stringjunky above (no offense intended): it shows a center.

[Spyman]

That is the reason why I dislike animations with balloon analogies like the one posted by stringjunky above (no offense intended): it shows a center.

The balloon analogy describes a closed Universe curved up on itself, all of the three spatial dimensions of space is located on the surface.

 

A common misconception is that the balloon is expanding into empty space that is "beyond the Universe" and that it is expanding from a single point in the center of the balloon. But the balloon analogy is a 2-dimensional model, and the center of the balloon and the space around are not part of the 2-dimensional Universe. In our 3-dimensional Universe, these points could only be reached by traveling in a 4th spatial dimension (not the time dimension of 4-D spacetime), but there is no evidence that this dimension exists.

http://www.astro.ucla.edu/~wright/balloon0.html

[michel123456]

The balloon analogy describes a closed Universe curved up on itself, all of the three spatial dimensions of space is located on the surface.

 

A common misconception is that the balloon is expanding into empty space that is "beyond the Universe" and that it is expanding from a single point in the center of the balloon. But the balloon analogy is a 2-dimensional model, and the center of the balloon and the space around are not part of the 2-dimensional Universe. In our 3-dimensional Universe, these points could only be reached by traveling in a 4th spatial dimension (not the time dimension of 4-D spacetime), but there is no evidence that this dimension exists.

http://www.astro.ucla.edu/~wright/balloon0.html

 

In the fight between image and text, image always win. If you show a balloon expanding into a black square, the people watching will see a balloon exapnding inside a black square. Point. You can add all the text you want after that explaining that blah blah blah, the image is there.

 

I should have stated I hate this kind of animations. They are doing more harm than anything.

 

P.S. your link is better, but IMHO the problems are still there.

Edited April 23, 2011 by michel123456

[Spyman]

I should have stated I hate this kind of animations. They are doing more harm than anything.

It is an analogy and not a full scale model, of course it has problems and of course a lot of people will misinterpret it.

 

If you can make a simple, better and catchy explanation accurately describing modern cosmology, you would surely become famous.

Edited April 23, 2011 by Spyman

[John Cuthber]

Yes all the pinpoints of light would be observable, but that infinite number of galaxies, extending to infinity, would also be very much smaller and dimmer the further they are, effectively invisible to us unless highly magnified. So the night sky of that universe remains dark.

Before we start expanding the universe, let's nail the issue of Olber for a static one.

The reply to Airbrush's comment is simple.

Q. what would be between all those bright points?

A Other stars

So the "gaps" would be bright too.

 

Olber was not an idiot.

[michel123456]

Before we start expanding the universe, let's nail the issue of Olber for a static one.

The reply to Airbrush's comment is simple.

Q. what would be between all those bright points?

A Other stars

So the "gaps" would be bright too.

Olber was not an idiot.

 

Isn't it exactly what we are observing?

Choose an empty part of the night sky, turn your telescope, and wait. What will be the result on the photographic plate?

Something like the Hubble Deep Field

 

"The HDF is at the centre of this image of one degree of sky. The Moon as seen from Earth would fill roughly one quarter of this image."

 

 

from Wiki.

 

At the end darkness is caused by our inability to see, not by the lack of astral objects.

Edited April 23, 2011 by michel123456

[IM Egdall]

It is an analogy and not a full scale model, of course it has problems and of course a lot of people will misinterpret it.

 

If you can make a simple, better and catchy explanation accurately describing modern cosmology, you would surely become famous.

 

 

I agree that coins on an expanding balloon analogy for an expanding universe has its limitations. But it has its merits too. When explaining it, I try to emphasize that the surface of the balloon represents our universe and only the surface. And the coins represent the galaxies and the coins/galaxies do not expand.

 

I ask my students to try to imagine being on one of those coins on that expanding balloon surface with no ability to sense outside that surface. From this point of view, all the other coins appear to be moving away from you. And the further away they are, the faster you see the coins move away (Hubble's Law). And there is no center to the surface of the balloon. And if you travel along the surface, you will never come to an edge. So this is an analogy for our universe having no center or edge.

 

As was pointed out - not a perfect analogy, but I do not know of a better one.

Edited April 23, 2011 by I ME

[random]

as per my previous post perhaps I was incorrect as to which sun's light took over 1000 years to reach us.

 

Since we have never seen the edge of the universe we do not know if it is infite or not, I thought I read somwhere though about a high powered telescope that took a picture of itself suggesting the universe is curved but I have no way to locate that article. Maybe someone with a better memory will know what I am talking about.

But even then the knowledge gained from that is limited because we know strong gravity (black holes) can bend light.

[StringJunky]

as per my previous post perhaps I was incorrect as to which sun's light took over 1000 years to reach us.

 

Since we have never seen the edge of the universe we do not know if it is infite or not, I thought I read somwhere though about a high powered telescope that took a picture of itself suggesting the universe is curved but I have no way to locate that article. Maybe someone with a better memory will know what I am talking about.

But even then the knowledge gained from that is limited because we know strong gravity (black holes) can bend light.

 

That was just a thought experiment to illustrate the curvature of space.

 

I ME

 

I find as long as I don't try and imagine the shape of the Universe from the 'outside' it all makes sense and I can picture the expansion in 3 dimensions...all the effects are relative to me within the Universe

Edited April 23, 2011 by StringJunky

[michel123456]

I agree that coins on an expanding balloon analogy for an expanding universe has its limitations. But it has its merits too. When explaining it, I try to emphasize that the surface of the balloon represents our universe and only the surface. And the coins represent the galaxies and the coins/galaxies do not expand.

(...)

 

Good for you.

 

But if you want to talk about surface & coins, why do you use a balloon which is 3D, and not use a stretched surface? It is better to remain in 2D all along.

 

Take your wife's panties, put coins on it and stretch. Your students will be enjoyed to help you stretching in all directions at the same time, especially if you are a female and got your panties off for the sake of science.

Edited April 23, 2011 by michel123456

[StringJunky]

Good for you.

 

But if you want to talk about surface & coins, why do you use a balloon which is 3D, and not use a stretched surface? It is better to remain in 2D all along.

 

Take your wife's panties, put coins on it and stretch. Your students will be enjoyed to help you stretching in all directions at the same time, especially if you are a female and got your panties off for the sake of science.

 

If you use a flat surface as an analogy you lose that part of the Balloon Analogy which explains how it can expand without an edge in sight and also a flat sheet analogy would imply that the Universe was expanding into a pre-existing space.

Edited April 23, 2011 by StringJunky

[pwagen]

According to the Big Bang theory there is no center or other fixed location inside the Universe that space is expanding from, space expands equally everywhere.

I think I understand how space itself is expanding (and not the galaxies simply moving further apart etc). But even acknowledging space is expanding "equally everywhere", wouldn't that still suggest everything was condensed in a single point, thus can be said to expand from there? Or is that just arguing semantics?

 

For example, looking at the image on this Wikipedia article:

http://en.wikipedia....ansion_of_space

 

namely this:

http://upload.wikime..._(Galaxies).png

 

Going back in time, those dots would be on top of each other, right? So can that position be said to be the place space is expanding from? Or would relativity kick in, so each point would see every other point moving away, right from the get-go, and each dot will always look like the origination of the universe no matter how you look at it?

 

Sorry for the silly questions, but my head won't easily wrap around these things.

[Spyman]

Going back in time, those dots would be on top of each other, right? So can that position be said to be the place space is expanding from? Or would relativity kick in, so each point would see every other point moving away, right from the get-go, and each dot will always look like the origination of the universe no matter how you look at it?

Going back in time will place the dots closer together but never precisely on top of each other, so each dot will always look like the center of the Universe.

 

Extrapolation of the expansion of the Universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past. This singularity signals the breakdown of general relativity. How closely we can extrapolate towards the singularity is debated—certainly not earlier than the Planck epoch.

http://en.wikipedia.org/wiki/Big_Bang

 

The earliest phases of the Big Bang are subject to much speculation. In the most common models, the Universe was filled homogeneously and isotropically with an incredibly high energy density, huge temperatures and pressures, and was very rapidly expanding and cooling.

http://en.wikipedia.org/wiki/Big_Bang

 

Maybe this explanation will be simpler than Wikipedia: Where was the center of the Big Bang?

[zapatos]

as per my previous post perhaps I was incorrect as to which sun's light took over 1000 years to reach us.

Perhaps you were thinking of the time it takes a photon to leave the sun...

 

The high-energy photons (gamma rays and x-rays) released in fusion reactions take a long time to reach the Sun's surface, slowed down by the indirect path taken, as well as by constant absorption and reemission at lower energies in the solar mantle. Estimates of the "photon travel time" range from as much as 50 million years[5] to as little as 17,000 years.[6] After a final trip through the convective outer layer to the transparent "surface" of the photosphere, the photons escape as visible light.

http://en.wikipedia.org/wiki/Solar_core

[MigL]

String Junky is correct. The observable universe is limited by the fact that the speed of light is finite and that the universe is expanding. That is all.

As we look farther and farther out we see objects receding faster and faster, ie their light is shifted more and more towards the red end of the spectrum. because the universal expansion is not constrained relativistically, at some distance, the recession speed is equal to c and the red shift is infinite, ie the wavelength of the light is infinite and so its energy is zero. That means we don't see it anymore.

The observable universe isn't due to finite size or time of existence.

 

Light takes 1000 yrs to reach the surface of the sun due to the absorption and re-radiation by solar plasma, it travels to the earth at speed c.

 

Assume you are correct and the universe is finite, and bounded, what do you see when you get to the edge ??? What is the edge made of which keeps everything from spilling out ?? What happens if you take a step past the edge, where are you ?? When you can begin to answer questions like these, then a finite bounded universe can be considered, until then K.I.S.S. and assume the universe is finite but unbounded ( warps back onto itself ) or infinite

[steevey]

That is the reason why I dislike animations with balloon analogies like the one posted by stringjunky above (no offense intended): it shows a center.

 

Well thats also weird that the observations happen to be that way, because studies by NASA claims to see the entire universe when it was some 300,000 years old using the microwave background, so I don't see why they don't just say that the reason we can't see a center is because the universe is a REALLY big place now, there'a matter everywhere and there's bun millions of interactions with galaxies changing their courses.

[IM Egdall]

Well thats also weird that the observations happen to be that way, because studies by NASA claims to see the entire universe when it was some 300,000 years old using the microwave background, so I don't see why they don't just say that the reason we can't see a center is because the universe is a REALLY big place now, there'a matter everywhere and there's bun millions of interactions with galaxies changing their courses.

 

 

Oy! The reason we do not see a center is because there is no center. This may violate your intuition, your assumptions, and your common sense; but this is what general relativity tells us about the universe.

[steevey]

Oy! The reason we do not see a center is because there is no center. This may violate your intuition, your assumptions, and your common sense; but this is what general relativity tells us about the universe.

 

No I completely understand why it would "look" that way, I'm just not entirely sure that it is actually that way since I can see the same principal with a static object. If I look at the certain comb completely parallel to the ground, then I see that the brussels close to the center aren't that separated by distance, and then the further I get away from the center, the further the brussels seem to be from each other, even though they are all equidistant from each other form region to region and there's a concrete center of the comb part (like lets say 6 form a hexagon with 1 in the center. The distance from the center ones for all the ones that make vertices are equidistant from the center one, only theres multiple hexagons and overlapping). There's also the fact that the universe is really big, and if we are near the center, it might be leading us to see that matter is equally scattered everywhere around us or in every direction, which it would be.

[Mr. X]

To my knowledge, an infinite universe doesn't go very well with an infinite one. Because if it's expanding, it's expanding from something. That means that it originates somewhere, and that means it's not infinite.

 

I read some old 60s book on astronomy that suggested an "ever creating" universe, which is basically creating matter out of nothing at some point, and then expanding like we think our universe does at the moment. So I guess that would be a valid universe by your example, but there's not a lot to suggest ours is one of those.

 

 

 

Well, what exactly is expanding?

We see the contents of the universe traveling away from something. Maybe their origin; as you say. But, does that mean the universe, or an infinite shell of the universe, was not already there?

[DrRocket]

Well, what exactly is expanding?

We see the contents of the universe traveling away from something. Maybe their origin; as you say. But, does that mean the universe, or an infinite shell of the universe, was not already there?

 

http://www.scienceforums.net/topic/33180-cosmo-basics/

[Spyman]

Observable universe

Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct experimentation about any part of the universe that is causally disconnected from us, although many credible theories require a total universe much larger than the observable universe. No evidence exists to suggest that the boundary of the observable universe constitutes a boundary on the universe as a whole, nor do any of the mainstream cosmological models propose that the universe has any physical boundary in the first place, though some models propose it could be finite but unbounded, like a higher-dimensional analogue of the 2D surface of a sphere which is finite in area but has no edge. It is plausible that the galaxies within our observable universe represent only a minuscule fraction of the galaxies in the universe.

http://en.wikipedia.org/wiki/Observable_universe

 

 

Copernican principle

In physical cosmology, the Copernican principle, named after Nicolaus Copernicus, states that the Earth is not in a central, specially favored position. More recently, the principle has been generalized to the relativistic concept that humans are not privileged observers of the universe. In this sense, it is equivalent to the mediocrity principle, with important implications for the philosophy of science.

...

Measurements of the effects of the cosmic microwave background radiation in the dynamics of distant astrophysical systems in 2000 proved the Copernican principle on a cosmological scale. The radiation that pervades the universe was demonstrably warmer at earlier times. Uniform cooling of the cosmic microwave background over billions of years is explainable only if the universe is experiencing a metric expansion.

http://en.wikipedia.org/wiki/Copernican_principle

[StringJunky]

Observable universe

Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct experimentation about any part of the universe that is causally disconnected from us, although many credible theories require a total universe much larger than the observable universe. No evidence exists to suggest that the boundary of the observable universe constitutes a boundary on the universe as a whole, nor do any of the mainstream cosmological models propose that the universe has any physical boundary in the first place, though some models propose it could be finite but unbounded, like a higher-dimensional analogue of the 2D surface of a sphere which is finite in area but has no edge. It is plausible that the galaxies within our observable universe represent only a minuscule fraction of the galaxies in the universe.

http://en.wikipedia.org/wiki/Observable_universe

 

Martin showed an interesting arxiv paper here once to help explain the cosmological expansion for us and it said (speculating) that eventually, in the extremely far distant future, the only stars we would be able to see were those in our Local Group because the light from the other superclusters would be outside the Observable Universe and therefore couldn’t reach us.

 

One consequence of this, it went on, was that if humanity somehow lost all it’s knowledge via a global nuclear war or some massive catastrophe and had to start again the cposmologists of the future would conclude that we live in an Island Universe surrounded by space...it would have an edge!

 

If we were having this conversation in that time, the people that are ‘wrong’ in this day would be ‘right’ in the future bercause that would be what the observational evidence suggests!

Edited April 26, 2011 by StringJunky

[michel123456]

Martin showed an interesting arxiv paper here once to help explain the cosmological expansion for us and it said (speculating) that eventually, in the extremely far distant future, the only stars we would be able to see were those in our Local Group because the light from the other superclusters would be outside the Observable Universe and therefore couldn’t reach us.

 

One consequence of this, it went on, was that if humanity somehow lost all it’s knowledge via a global nuclear war or some massive catastrophe and had to start again the cposmologists of the future would conclude that we live in an Island Universe surrounded by space...it would have an edge!

 

If we were having this conversation in that time, the people that are ‘wrong’ in this day would be ‘right’ in the future bercause that would be what the observational evidence suggests!

 

IMHO this reasoning shows that our concepts are wrong.

 

IMHO again, the Copernican Principle must be enlarged: we are not only anywhere in the Universe, we are also at anytime. What we observe today must be the same as yesterday and the same as tomorrow. A full Mediocrity Principle in Space and in Time.

[DrRocket]

IMHO this reasoning shows that our concepts are wrong.

 

IMHO again, the Copernican Principle must be enlarged: we are not only anywhere in the Universe, we are also at anytime. What we observe today must be the same as yesterday and the same as tomorrow. A full Mediocrity Principle in Space and in Time.

 

That is what Bondi called the "perfect cosmologicalrinciple". It leads to s steady state theory of cosmology as advanced by Hoyle or Bondi and Gold.

 

These theories intuitively appealing, relatively simple and wrong.

[StringJunky]

IMHO this reasoning shows that our concepts are wrong.

 

IMHO again, the Copernican Principle must be enlarged: we are not only anywhere in the Universe, we are also at anytime. What we observe today must be the same as yesterday and the same as tomorrow. A full Mediocrity Principle in Space and in Time.

 

The paper didn't discredit present understanding at all, in fact, it was explaining it but it added an interesting and alternative conceptual scenario if our accumulation of knowledge were to suffer some abrupt discontinuity in the future. I might try and find it later.

Edited April 26, 2011 by StringJunky