The Most Distant Object Discovered in the Universe - Page 3

On May 07 2009 16:47 shavingcream66 wrote:
who cares :X

On May 06 2009 17:44 Thats_The_Spirit wrote:
A little more than a week ago scientists discovered a gamma ray burst from outer space lasting 10 seconds with a redshift of 8,2. It is calculated that the source is more than 13 billion lightyears away, probably an explosion of a star.
Because of the finite speed of light, observing a lightsource 13 billion lightyears away also means observing an explosion that happened 13 billion years ago, only about 600 million years after the birth of the universe (according to the big bang theory).

Source:
http://www.eso.org/public/outreach/press-rel/pr-2009/pr-17-09.html

At first i just thought it was cool that we are able to observe this kind of stuff. After a while I gave it some more thought:
How is it that we are able to observe light from an explosion that happened more than 13 billion years ago?
To answer this question, assuming the most popular theories of physics (and my knowledge of it) and the method of measurements are correct, I thought of the following:

During the first couple of million years the universe had to be expanding at a rate tremendously faster than the speed of light. If this wasn’t the case then the light of the explosion would have passed our location in the universe a couple of billion years ago (because of the limited side of the universe at an age of 600 million years) and we never would have been able to see it.
After a while the expansion rate had to slow down, or the light wouldn’t be able to catch up to us, and we again wouldn’t be able to see it.

Recent observations show that the galaxies surrounding us are moving away from us at an increasing rate, indicating that the expansion of the universe is accelerating again?

I don’t know if what I’m saying is correct, cause I don’t have a background in physics. But I think this observation can cause more interesting thoughts and a nice discussion. And maybe a person with a background in physics can shed some light onto this.

On May 06 2009 19:22 Thats_The_Spirit wrote:


I've read "stars and falling apples" by ulf danielsson. I think it was really good and easy accessible by people without a background in physics. It covers the different theories (including relativity, and string) and other things about the universe and explains them with good and understandable examples.
Also i liked "a brief history of time", by stephen hawking

On May 07 2009 01:17 ilj.psa wrote:

Define "infinitely dense singularity."

On May 07 2009 18:35 Cascade wrote:

Most distant if you don't count background radiation that is.
(self advertising of my old writeup on cosmic background radiation)


ok. Thing here is that you shouldn't have the image of the universe as a pancake that grows, but rather an image of an inflating balloon as proposed by other posters. So light passing us first time will not go on and hit the "end of the universe" (no such thing exists), but it will rather continue around the balloon and could possibly hit us on the second passing, or third etc.


If you trust this observation (WMAP satellite iirc), then yes, the expansion of the universe is accelerating. There have recently been some doubts on this experiment though, but i'm not sure about the details. You would have to research that further if you want an up to date view of that.


That'd be me.

Let me also comment on this "faster than light expansion".
As many pointed out, the relativity bound of "impossible to go faster than light" cannot be used here. Reason is that what we actually measure is not only the relative speed between the earth and a distant star in an instance (this is bounded by light speed), but we measure also how fast the space grows in between us (this comes from the increased redshift while the photons are traveling). The rate with which extra space is created between us is not limited by light speed, since it cannot be seen as a relative speed between two objects, and special relativity do not apply.

What people normally mean when they talk about the universe expanding faster than light is the following:
Let's talk about the inflating balloon again. Place an ant at a certain point on the balloon, and let it start moving towards an other point on the balloon. As it moves, it will come closer to the other point, but the point will also get more distant as the balloon inflates. If the balloon is inflated fast enough, the ant will never reach the other point.

Now replace the balloon with the universe, the ant with a beam of light, and you will understand what is meant with the universe growing faster/slower than light. As has also been said already, during inflation in the first fraction of the second of the universe, the universe expanded (much) faster than light in this sense, but by the time stars were formed, it had since long slowed down below light speed.

ok, I hope I contributed with something, back to work now for me.
hf guys.

On May 07 2009 05:41 Luddite wrote:


Usually when you talk about things going faster than light speed, what it means is that the light wasn't in a vacuum (light goes slower through matter than it does through a vacuum). But if you really want to "break the speed of light", in other words to have something faster than light, in a vacuum, in the same reference frame, you'd pretty much need to prove that the theory of relativity is wrong, because the theory is quite clear about that (as speed goes to C, energy increases to infinitiy, so you'd need an infinite amount of energy to get to light speed. Interestingly the mathematics DO allow for something which is already traveling faster than light speed, and which could never slow down below C. But that wouldn't really make much sense). Anyway I wouldn't bank on relativity being wrong since it's been tested countless times and it's ALWAYS help up perfectly.

On May 07 2009 18:35 Cascade wrote:
As has also been said already, during inflation in the first fraction of the second of the universe, the universe expanded (much) faster than light in this sense, but by the time stars were formed, it had since long slowed down below light speed

As the Universe expands, the density of dark matter declines more quickly than the density of dark energy (see equation of state) and, eventually, the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved but the density of dark energy is nearly unchanged (it is exactly constant for a cosmological constant).

On May 07 2009 15:43 Thats_The_Spirit wrote:


Makhno is referring to "the best of all possible worlds" by ulf danielsson, not brian greene. I've found that the english version is also called "the best of worlds"

And Makhno, that is really cool that hes at your university. Did you ever attended any of his lectures? I'll see if i can find his newest book you talked about, the reviews i've found show that it's an interesting read.

On May 08 2009 06:38 sith wrote:


Uhh not sure how I misread that conversation thread. I feel retarded.

I still I can't find this book though, under either name.