expansion of the universe

[rafman400]

So basically the idea is that the whole of the universe is expanding. The most common analogy I have seen is the balloon analogy depicted here:

 

This is where Im supposed to post a picture of the expanding universe balloon. Just image search "expanding universe balloon" and you'll see it

 

This analogy must he broken.

 

If the universe is expanding, then the galaxies are expanding. If the galaxies are expanding,than the bodies in them must be expanding. If all that is true than we,as physical bodies, must also be expanding!!

 

Think about putting a little dot in one of those galaxies on the balloon to represent yourself. You'll see that it also expands.

 

So if the only motion we can really measure is relative motion, this model really shows that we are all expanding at the same rate relative to each other so really we should NOT be noticing anything.

 

If you sitting on your computer expanded and your computer expanded and everything else in your room also expanded at the same rate than you wouldn't notice it.

 

A truly uniform expansion should not be visible to one within said universe.

 

What I'm asking is, is this a bad analogy and and isthe universe "stretching"/expanding or .... What?

[pwagen]

A thread only a few days old answers this question:

http://www.scienceforums.net/topic/72570-how-can-galaxies-exist-with-the-expansion-of-space/

 

 

 

Think about putting a little dot in one of those galaxies on the balloon to represent yourself. You'll see that it also expands.

Try gluing coins to your balloons. You'll see the universe (balloon) expands on the big scale, but galaxies (coins) stick together locally due to gravity.

 

 

What I'm asking is, is this a bad analogy and and isthe universe "stretching"/expanding or .... What?

I've actually heard it's a crappy analogy, but I can't remember why it was said so. However, to very basically show how the universe expands, it could probably be worse.

[rafman400]

thank you for the response! The thread was helpful and i've read some more explanations with the analogy of raisins in a cake when being baked. I see that the determining factor here is gravity. What i am getting from these explanations are that it is the space that we occupy that is expanding and not us....BUT i still find it hard to swallow.

 

As light travels between galaxies it is stretched by this phenomenon causing the red shit.

 

So If you take out light and put me in between these galaxies would I stretch too?

 

 

Try gluing coins to your balloons. You'll see the universe (balloon) expands on the big scale, but galaxies (coins) stick together locally due to gravity.

 

The problem with this is when you "play it in reverse" or rewind the inflation you'll come to a point when the composite of all the galaxies is larger than space itself.

 

I really feel like there are too many holes in this thing, and yet accepted without much explanation except for some observations throughout various experiments.

[StringJunky]

thank you for the response! The thread was helpful and i've read some more explanations with the analogy of raisins in a cake when being baked. I see that the determining factor here is gravity. What i am getting from these explanations are that it is the space that we occupy that is expanding and not us....BUT i still find it hard to swallow.

 

As light travels between galaxies it is stretched by this phenomenon causing the red shit.

 

So If you take out light and put me in between these galaxies would I stretch too?

 

No. The atomic bonds that hold you together are far stronger than cosmological expansion.

 

 

...The problem with this is when you "play it in reverse" or rewind the inflation you'll come to a point when the composite of all the galaxies is larger than space itself.

 

I really feel like there are too many holes in this thing, and yet accepted without much explanation except for some observations throughout various experiments.

 

You have to be careful not to push an analogy too far...they are not meant to be, nor can be, totally accurate. all the penny/balloon analogy is meant illustrate is the intra-galactic components not being affected by the forces of expansion due to their combined gravity.

 

Don't forget galaxies are evolving too. As you go back in time they become more gaseous in structure and the makeup of the universe becomes more homogenous.

 

 

 

 

.

Edited February 23, 2013 by StringJunky

[rafman400]

Thanks for the reply. I know it can be annoying repeatedly explaining something, but this expansion thing confuses me. I know I'm really pushing these analogies, but I just think they shouldn't be used at all because they only confuse and demonstrate an expansion of a different nature, not the one currently occurring.

 

What you said here really strikes a chord with me though:

 

No. The atomic bonds that hold you together are far stronger than cosmological expansion.

.

 

To me it seem like those things aren't even playing the same game of "tug of war". Cosmological expansion is not force(right?). It seems to me that cosmological expansion is not a physical stretching but a dimensional stretching and if my atoms stretched along with it, in a dimensional way (not physically), than the bonds would hold.

 

If we lived in a universe where nothing seems to move, everything could still be expanding but nothing would be noticed since everything relative to itself stays the same.

 

Im no physics expert but to me detecting an actual expansion of the universe aka the dimensions we live in (remember no galaxies are actually moving away from each other, they are stationary) would be extremely difficult. I mean what implications would this even have for time!?

 

The evidence seems weak to me. And newer observations seem to throw out the old rate and put in a new one. I don't see how this is immediately taken as fact. When i search for proof i get the Hubble observation and some quantum theory.

 

really?

 

My gut tells me its a trick of the light. Much like when seeing two stars when actually the light is being gravitationally(not a word) split by a third massive star.

 

again, i am no expert.

Edited February 23, 2013 by rafman400

[pwagen]

The evidence seems weak to me. And newer observations seem to throw out the old rate and put in a new one.

It's not that bad, is it? The expansion of the universe has been known for like 80 years, so that hasn't changed a whole lot. The details and our knowledge of it has improved though. We now know the expansion is actually accelerating, which at first glance doesn't seem possible. We know about the inflation period, which we wouldn't know back then. So the theories improve all the time, but I wouldn't say new theories take the place of old ones in this case. After all, the basic idea of the Big Bang and an expanding universe haven't changed.

 

As for gut feeling speaking up against these ideas, I can understand where you're coming from. Myself, I had a very hard time understanding something as simple as Einstein's E=mc^2. I accepted it, partly because I trusted scientists knew what they were doing. But also because they built bombs based on the equation, so it obviously worked. This all changed, however, in physics class at one point, when we were learning about it. Out of nowhere it seemed, we suddenly deduced that very equation, and it all made sense to me. So the only advice I can give you if you don't trust the evidence is to learn about it and do the works yourself. If you take the time and dedication to actually try and understand it, I'll guarantee the evidence will add up!

[elfmotat]

Read the whole thread pwagen posted, because you're essentially asking the same question that he was. Understanding what "expanding space" means requires knowledge of General Relativity, or at least some experience in working with a metric. The best way to demonstrate why galaxies are accelerating away from us without using any GR is with the Newtonian approximation with nonzero Cosmological Constant:

 

[math]F=m \left (- \frac{GM}{r^2}+\frac{c^2 \Lambda r}{3} \right )[/math]

 

The second term acts as a repulsive force so that when you get far enough away from a gravitating mass, gravity actually becomes repulsive. Up close, gravity is still attractive because the first term dominates the second. In Newtonian gravity the space is static and unchanging, so you don't need to worry about expansion. Keep in mind that this is just an approximation to GR.