Expanding universe

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Expanding universe

Postby SirDice » Wed Nov 04, 2009 7:50 pm

This is something I just can't seem to wrap my head around, I've been pondering this for quite some time now.
Googled it, read a lot on the subject but found nothing conclusive except it's the exact opposite of what I'm thinking.
Hundreds of astronomers can't be wrong so I must be missing something crucial.

Here's the deal, Hubble found out that far away galaxies and objects move faster then the ones close by.
This is pretty much the cornerstone of the idea that the universe is expanding and it's doing this at an increasing rate.

Now I'm thinking, when you measure the speed of something at say 10 billion light years away you are actually measuring the speed it had 10 billion years ago.
Not it's current speed. So objects closer by move slower but the speed measurement is also younger.

If you put the time vs. speed in a graph starting at T-13.7 billion years ago with T the current time, you will see the speed is actually decreasing.

So how do they get to the conclusion that the universe is expanding at an increasing speed?
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Re: Expanding universe

Postby Aspman » Thu Nov 05, 2009 10:18 am

I belive it's related to doppler shift. The frequency of light from objects further away has shifted further than those that are closer.

A recent one about the origins of the universe that screwed my brain was that before the big bang what was there...and one physicist said they there wasn't necessarily the 4th dimension of time therefore there didn't have to be a before [the big bang] and ther5e doesn't have to be an after
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Re: Expanding universe

Postby SirDice » Thu Nov 05, 2009 10:55 am

Aspman wrote:I belive it's related to doppler shift. The frequency of light from objects further away has shifted further than
those that are closer.

Yeah, I get that whole redshift thing. Besides the movement that causes the shift (as with sound and the doppler effect), the expension of space also contributes to the redshift.

I'm not saying the universe isn't expanding, I get that bit. It's the increase of the rate I just don't get.


A recent one about the origins of the universe that screwed my brain was that before the big bang what was there...and one physicist said they there wasn't necessarily the 4th dimension of time therefore there didn't have to be a before [the big bang] and ther5e doesn't have to be an after

Well, Einstein said that space and time are the same thing, hence the term space-time. So if space didn't exist before the big bang time didn't either.
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Re: Expanding universe

Postby Aspman » Thu Nov 05, 2009 12:32 pm

SirDice wrote:
Aspman wrote:I belive it's related to doppler shift. The frequency of light from objects further away has shifted further than
those that are closer.

Yeah, I get that whole redshift thing. Besides the movement that causes the shift (as with sound and the doppler effect), the expension of space also contributes to the redshift.

I'm not saying the universe isn't expanding, I get that bit. It's the increase of the rate I just don't get.


The expected shift Vs distance isn't linear as would be expected if the expansion was constant, the redshift is a curve.
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Re: Expanding universe

Postby SirDice » Thu Nov 05, 2009 2:27 pm

Aspman wrote:The expected shift Vs distance isn't linear as would be expected if the expansion was constant, the redshift is a curve.

But Hubble's measurements show it is, at least for distances smaller than the radius of the Hubble Sphere.

http://en.wikipedia.org/wiki/Hubble%27s_law
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Re: Expanding universe

Postby Aspman » Thu Nov 05, 2009 4:03 pm

Oooh that's got maths and stuff in it. Plus some algebra with squiggly lines.

I think my fag packet cosmology has reached it's limit.
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Re: Expanding universe

Postby rapier57 » Thu Nov 05, 2009 5:11 pm

I'm coming into this from old school, so bear with me. The Law of Thermodynamics addresses the exchange of energy between physical systems and the loss during the exchange: entropy. That is a law, not a theory. Then there is the Law of Gravity. Gravity is a constant throughout the universe and is--basically--the glue that holds it all together. Gravity plays a part in generating entropy, since it affects physical systems.

The speed of light is another constant, 186,000 mps. Constant enough for our purposes, anyway.

Now, when we look at things in space, we see them from a time and distance perspective. Some things are moving toward us, some things are moving away from us. Some things move in a similar direction and speed relative to us. So, this provides some directional flow for us to use to postulate that there was a big bang, so to speak.

The Hubble (and future similar platforms) gives us an opportunity to view deeply into areas we have not been able to resolve before. And, measure distance and speed. However, you still have to factor that light takes a certain amount of time to reach us. Yes, SD, some things moving away from us seem to be "moving faster" than originally thought. This would seem to fly against the LoT and entropy. But, you are correct in that we are seeing the blue shift or red shift from a much more distant (time and space) light signal. It is entirely possible--very likely--that the objects we are trying to measure are no longer moving at that speed. LoT, gravity and entropy apply here, as everywhere.

If we look "the other direction" we see things moving from what seems to be a source location. Of course, the same effects apply to what we observe with regard to the light. So, like the three blind men and the elephant, we postulate from our perspectives and assume that everything is moving away from a central point. As far as we know, the universe is infinite. In an infinite universe, is it not possible that we see such a small part that we make erroneous conclusions of the size and shape of the universe, based on our observations?

It is possible that the universe is not expanding, but that we are just a small part moving in a flow.

I would speculate that the part we see coming and the part we see going are the part of the universe in which we are positioned that is revolving around a central core, much like a galaxy. This in itself could be moving around in a similar pattern in a larger dance.

Interesting discussion. James Blish addressed this in the Cities in Flight series. Of course, he assumed that at some point the collapse as entropy reached equilibrium would occur very quickly--almost instantaneously--and another "big bang" almost immediately after. And, this all occurred in the lifetime of the characters, long-lived as they were.
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Re: Expanding universe

Postby Timaxe » Fri Nov 06, 2009 3:29 am

Suppose we have a elastic strap anchored somewhere. There are 2 marks on it - the first one is 1 inch from the anchor point, and the second one is 10 inches from the anchor point. When we stretch the strap, consider how far the 1st mark travels from the anchor point. Now consider how far the 2nd mark travels. This is probably the underlying concept for things further away traveling faster away from us in an expanding universe. For fun, how far apart have the marks traveled from each other?

Now suppose we could only measure with the velocity "c", which is a constant for all of the above measurements, and not the actual distance "x". How far apart are the marks if we're continuing to stretch the elastic strap, and at what point can we no longer observe the marks? :D


Note: I don't know too much about astronomy and relativity, but it is interesting thinking of what it means to be in an expanding universe (where gravity isn't a large influence) with the speed of light being held constant. Strange things happen to concepts such as time and the definition of something familiar like distance...
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Re: Expanding universe

Postby SirDice » Fri Nov 06, 2009 10:44 am

Nice analogy :) Someone explained the concept to me using a balloon with marks on it. It nicely explains why most galaxies move away from us, except a few that are actually on a collision coarse with the milky way :shock: . It also explains that just because everything moves away from us we're not in the center of the universe. Because from the vantage point of every single dot on that balloon all the others are moving away from it.

I get all the expansion stuff, I just can't figure out if the rate of expansion increases (over time things move faster and faster away) or if it decreases. As rapier noted, gravity plays a big role in this. If the expansion rate decreases it might some day stop completely and start contracting everything again due to gravitational forces (the big crunch).

But because the rate is increasing they figure this must be caused by something else. Most bet on dark energy/matter, whatever the hell that may be..
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Re: Expanding universe

Postby SirDice » Fri Nov 06, 2009 10:44 am

Nice analogy :) Someone explained the concept to me using a balloon with marks on it. It nicely explains why most galaxies move away from us, except a few that are actually on a collision coarse with the milky way :shock: . It also explains that just because everything moves away from us we're not in the center of the universe. Because from the vantage point of every single dot on that balloon all the others are moving away from it.

I get all the expansion stuff, I just can't figure out if the rate of expansion increases (over time things move faster and faster away) or if it decreases. As rapier noted, gravity plays a big role in this. If the expansion rate decreases it might some day stop completely and start contracting everything again due to gravitational forces (the big crunch).

But because the rate is increasing they figure this must be caused by something else. Most bet on dark energy/matter, whatever the hell that may be..
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Re: Expanding universe

Postby Ignatius » Fri Nov 06, 2009 3:12 pm

This whole thing has my head in knots. I'm not sufficiently bright (in this area!) not to believe in the Big Bang and have accepted that everything in the universe at T=0 was compressed into a single point. However ... if the universe is expanding, what's it expanding into?
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Re: Expanding universe

Postby SirDice » Fri Nov 06, 2009 3:42 pm

That bit is still somewhat beyond me, including the bit about what was before the big bang :mrgreen:

Most of what I understood deals with M-theory, which is more or less an expansion of string theory. It deals with multiple dimensions and the idea is that in those 11 dimensions there's something called branes. These branes vibrate and when 2 branes make contact a huge amount of energy will be released. This generates "bubbles" of energy and one of those bubbles is our universe. Interesting enough this also opens up the idea on multiverse or multiple universes :swoon:

http://en.wikipedia.org/wiki/M-theory
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Re: Expanding universe

Postby Aspman » Fri Nov 06, 2009 5:48 pm

SirDice wrote:That bit is still somewhat beyond me, including the bit about what was before the big bang :mrgreen:

Most of what I understood deals with M-theory, which is more or less an expansion of string theory. It deals with multiple dimensions and the idea is that in those 11 dimensions there's something called branes. These branes vibrate and when 2 branes make contact a huge amount of energy will be released. This generates "bubbles" of energy and one of those bubbles is our universe. Interesting enough this also opens up the idea on multiverse or multiple universes :swoon:

http://en.wikipedia.org/wiki/M-theory


that what got me on the brane theory. before the big bang there wasn't necessarily a before because there may not have been time as such. So how did anything happen.

I belive it is a proven theory that the rate of expansion is increasing and the previous thought that the rate would have decreased due to the actions of gravity haven't been borne out. This is where the dark matter, dark energy and superstring theories kick in and they are in no way proven yet.
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Re: Expanding universe

Postby Harbinger » Sat Nov 07, 2009 7:02 am

It would seem to me that, like many, perhaps the speed of light is not at a constant at which it once was, or at least under certain circumstances. A vaccum of human creation is not truely empty, so I would not be surprised if the experimentation is off. I imagine that the outside of the universe is closer to holding absolutely nothing, which through simple laws of thermodynamics and inertia would explain why the boundries of the universe are accelerating ever faster.

The main problem with that is there are too many unknowns, and no existing human technology truely capable of testing it. Astrophysics is something where I am merely a layman though. Any knowledge of physics I have is mostly specialized to the elemental and molecular levels.
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Re: Expanding universe

Postby keezel » Sun Nov 08, 2009 2:35 am

"before the big bang" there wasn't necessarily a before because there may not have been time as such. So how did anything happen.


I'll admit this is way over my head, but it seems illogical to me to suppose that prior to the big bang, time did not exist. It's difficult enough to wrap my head around the thought that up until the big bang, all matter was contained within a near infinitely dense point. To go further and suppose that prior to the "bang" time did not exist just seems illogical. Is it not more logical to suppose that this point existed in a vacuum for an indeterminable span of time?

There are other theories that postulate that the big bang/big crunch cycle has happened before, which would also suggest that time has existed prior to the most recent "big bang".

My final thought: I once heard an apologist state that the first step in deciding between being an atheist or a theist is to determine if one believes that matter has always existed or if some greater power that has always existed brought that matter into being. With what we know now, we are unable to explain how matter could come into being on its own, therefore it either must be eternal OR something else that is eternal brought the matter into existence. I think this argument will hold true until science is able to explain more about the mystery of the big bang event, because as it stands now we simply do not know enough about it. Even then the argument may still be valid depending on what we learn.

That should stir up some interesting debate. :mad:
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