Starship Asterisk*

Just as a matter of interest. And not just for me.

1 Astronomers talk of expansion accelerating. How fast is expansion at the moment? And how much is it increasing per year?

2 How long will it be, before expansion Becomes so fast we can no longer see all the stars and galaxies?

3 Why After 13.7 billion years, is expansion accelerating Now?

4 What Is Entropy And does this effect acceleration?

5 What tell tell signs say the universe expansion is accelerating?

6 Why does the universe have less time left than previously thought as described below?

http://www.cosmosmagazine.com/news/3263 ... ly-thought

Day one no Answer.

If I get to 7 days do I get Any Points?

Mark

Google "Hubble Constant" and see if that helps.

Mark, awhile back you posted several questions here, one of which was about entropy. If you haven't come across this recent online article in Wired Science, you might be interested in following this link:

http://www.wired.com/wiredscience/2010/02/what-is-time/

jacklap wrote:Mark, awhile back you posted several questions here, one of which was about entropy. If you haven't come across this recent online article in Wired Science, you might be interested in following this link:

http://www.wired.com/wiredscience/2010/02/what-is-time/

Thanks Mate.

Much appreciated. Book marked already.

Mark

Years ago in a P-Chem class, any explanation of entropy I came across was a bit stuffy, as I supposed it had to be. I do like the very informal explanation of entropy in the Wired Science article, that (at some level) you could accept a neatly stacked pile of papers on your desk when you left the office to be in disarray when you returned. On the other hand, you might be at a completely surprised if you left papers on your desk in a big mess and came back later to find them ordered and neatly stacked. Dr. Carroll was referring to the "arrow of time" being unidirectional and its cosmological implications, but I wonder if he realized that maybe it's something that humans intuitively understand. We seem to accept the fact that as hard as we try to construct and maintain order in our "universe", in time it will deconstruct to disorder. But we should never give up trying!

Hi,
some answers to Questions above:
1. the speed of expansion depends on how far the objects are. there is this equation, V=h.D, which you can calculate the speed of expansion in a specific region using it. V is Speed of expansion, D stands for distance (in parsec) and h is hubble constant, which is around 71.you can find the exact number in wikipedia.
and why does it depend on distance? because it's just like a balloon! we dont have a center for expansion. when you're blowing a balloon, the spots with less distance get away from each other with a less speed than the spots with more distance. the expansion in our universe is like the one in balloon, except the universe is expanding in 3 Dimensions.

2. based on the first answer, i guess there would be a distance which the objects get away from us with such a speed that their light shifts out of visible band of Spectrum then we can not see them, but we can detect them.
although I'm not so sure of my answer, because i don't know if visible light can shift out to radio wave or not. can it?
but assuming it can, you have to calculate the enough speed for shifting the objects light, then put the speed in the first equation to find the distance that the object could not be seen further than that.

3. the expansion was always accelerating, but we just discovered in lately!
but the point is that the bigger the universe becomes the more expansion accelerates.

4. i never heard of it, does it affect?

5. well one of the clues is that we receive a red light from a star which is not that red itself!
more specifically the light that travel a long distance along the universe, become red-shifted.
why is that? because as the universe expands, the space that light is traveling in stretches. and increases the wave length of light.

Hi Amir

Thank you for your time.
1

Amir wrote:1. the speed of expansion depends on how far the objects are. there is this equation, V=h.D, which you can calculate the speed of expansion in a specific region using it. V is Speed of expansion, D stands for distance (in parsec) and h is hubble constant, which is around 71.you can find the exact number in wikipedia.
and why does it depend on distance? because it's just like a balloon! we dont have a center for expansion. when you're blowing a balloon, the spots with less distance get away from each other with a less speed than the spots with more distance. the expansion in our universe is like the one in balloon, except the universe is expanding in 3 Dimensions.

mark swain wrote:1 Astronomers talk of expansion accelerating. How fast is expansion at the moment? And how much is it increasing per year?

My motives for this Question. Were based on a faster than Light first expansion rate, to then slow down, And Later accelerate again. In the universes "life time" .

2

Amir wrote:2. based on the first answer, i guess there would be a distance which the objects get away from us with such a speed that their light shifts out of visible band of Spectrum then we can not see them, but we can detect them.
although I'm not so sure of my answer, because i don't know if visible light can shift out to radio wave or not. can it?
but assuming it can, you have to calculate the enough speed for shifting the objects light, then put the speed in the first equation to find the distance that the object could not be seen further than that.

mark swain wrote:2 How long will it be, before expansion Becomes so fast we can no longer see all the stars and galaxies?

My motives for this Question. Were based on acceleration increasing, back to faster than light. If this happens we will start to lose the distant galaxies from view.

3

Amir wrote: the expansion was always accelerating, but we just discovered in lately!
but the point is that the bigger the universe becomes the more expansion accelerates.

I do not think this was always the case. accelerating expansion was never constant at one speed. My question is asking why?

4

jacklap wrote:Mark, awhile back you posted several questions here, one of which was about entropy. If you haven't come across this recent online article in Wired Science, you might be interested in following this link:

http://www.wired.com/wiredscience/2010/02/what-is-time/

And a very interesting read, Thank you.

5

Amir wrote:well one of the clues is that we receive a red light from a star which is not that red itself!
more specifically the light that travel a long distance along the universe, become red-shifted.
why is that? because as the universe expands, the space that light is traveling in stretches. and increases the wave length of light.

Understood.

Thanks Amir.

welcome! I'm glad at least one of my answer was useful to you.
but after explaining your motives, I'd like to add some stuff:

1. i don't exactly know what you mean by "a faster than Light first expansion rate, to then slow down, And Later accelerate again. In the universes life time". but the first thing that comes to my mind is "Inflation Theory".
this theory, which is now a part of Standard Model, explains the homogeneity of universe (which is so unexpected) by saying that just after big bang an Inflation which lasted 10^-36 Seconds caused that tiny spot to expand to almost the size that our universe now is!
well, as the Inflation lasted just a tiny fraction of second, i think this will be the point it slows down, and then dark energy causes a new, rather much slower, expansion until now.

2. i believe regardless of red shift affect, we wont lose their light even if they move away faster than light!
let me explain: if you sit in a car which is moving 20m/s, and throw a stone with 5m/s (in the same direction), the speed of the stone will be 25m/s. and 15m/s if you throw it in the opposite direction.
if i got you right, you mean as the galaxies get away with speed of light, then there would be no light coming to us.
what happened to the stone, would never be true about light, because the speed of light is always a constant, and would never change due to the speed of light source or the observer.

3. i didn't say expansion was always constant at one speed, there was no "one speed" for whole universe at any time. because the speed varies with distance.
i can't say what the "why?" you wrote applies to, but if it says "why expansion was not always at one speed?", i repeat: because it varies with distance. and as the whole universe becomes bigger, and the distances increase, the speed of expansion increases too, in other words it accelerates.

Sorry if i got any of your questions wrong again, i did my best to comprehend.

and last time, a question came to my mind, I'll ask it again:
is it possible for the visible light to be red-shifted out of visible band of spectrum? shift into Infra-Red for instance?

Amir wrote:is it possible for the visible light to be red-shifted out of visible band of spectrum? shift into Infra-Red for instance?

Yes, see Hubble News Release STSci-2009-31 from Dec 2009, the latest Hubble Ultra Deep Field in near infrared.

That UDF near IR image would be great to see overlayed on a blink comparison with the same area in visible light