Osm bsm Y.

this answer is what spawned my new question, and thanks eh for the answer. i opened a new post because it didn't really fit to what was being discussed as the head topic on the other post.

if there was ever a time when matter or energy expanded/traveled faster then the speed of light/gravity, how could that expansion/travel be stopped?

doesn't this poke a hole in faster then light/gravity travel, even in inflation theory?

something about inflation theory doesn't jive for me =(

cfgauss

There's no trouble going faster than light is now then, if light was faster then!

eh

No signal can go faster than the speed of light, but there in no limit to hav fast space itself can expand. Or at least, that's what they say.

cfgauss

Nope, space is limited to expand (or move in any way) at exactly c.

Hawkingfan

Wrong, eh? I copied it straight from "A Brief History of Time". Do you want me to give you the page numbers?

Hawkingfan

That is 100% false. Are you familiar with Einstein and the theory of relativity?

Yes, time IS a dimension of space-time. But it is NOT ABSOLUTE. If two observers who are travelling at different speeds and are observing the same object travelling through space, they will disagree on the distance it travelled, and therefore DISAGREE on the time it took the object to get there! (my post below illustrates this better). Therefore, time is relative. This is one of the greatest contributions Einstein has made to the understanding of the universe.

Hawkingfan

Here is a great website that explains Einstein's 2 theories of relativity:

http://web.wt.net/~cbenton/relativity.htm

After it explains it in layman's terms, it has a quiz using thought experiments to see how well you understand it. I'll include experiment #2 and #3 from the site.

Experiment 2: Mrs. Einstein is standing in a field. Next to her is a light clock. That is, two mirrors that are reflecting a beam of light back and forth, and the journey from one mirror to the other and back again counts as one tick of the clock. Also, Mrs. Einstein is wearing a watch that is synchronized with her light clock.
Standing on a railroad car is Mr. Einstein. He also has a light clock, and his clock is synchronized with Mrs. Einstein's and his own wristwatch. The railroad car is not moving.
(the site shows a picture here of the setup)

Question: What happens?
Answer: Nothing unusual happens. Mr. Einstein's watch and clock stay perfectly synchronized with Mrs. Einstein's.

Now,

Experiment 3: We now have the same set up except that the railroad car is now moving to the left with a velocity v.


(the site has a picture here of the setup)

Question: What happens?
Answer: From Mr. Einstein's perspective, the beam of light keeps going up and down between the mirrors, but from Mrs. Einstein's perspective, the light now has to travel a diagonal path from one mirror to the other. Since Mrs. Einstein still measures the speed of light as c, she is now going to observe Mr. Einstein's light clock as ticking slower than hers since the light now has a longer distance to travel. However, since Mr. Einstein still experiences his watch as being synchronized with his clock, Mrs. Einstein will see his watch slow down along with his clock!
Conclusion: If someone moves in a straight line with velocity v with respect to you, then you will observe time passing more slowly for them.
With a little algebra we can compute exactly how much time will slow down.

In the millenium issue of "Time" magazine where Einstein was named man of the century, experiment #3 appeard in one of the articles to show how time is relative. You can probably see a copy online at "Time" magazine.

Hawkingfan

from one of the many articles on Eistein at Time Magazine--http://www.time.com/time/time100/scientist/profile/einstein.htm/

BY FRANK PELLEGRINI

Everything's relative. Speed, mass, space and time are all subjective. Nor are age, motion or the wanderings of the planets measures that humans can agree on anymore; they can be judged only by the whim of the observer.

Hawkingfan

From Stephen Hawking's article "A Brief History of Relativity" appearing in the Millenium Issue of Time magazine where Einstein was named man of the century:
http://affiliate.timeincmags.com/tim...of_rela6a.htm/

In that 1905 paper, Einstein pointed out that because you could not detect whether or not you were moving through the ether, the whole notion of an ether was redundant. Instead, Einstein started from the postulate that the laws of science should appear the same to all freely moving observers. In particular, observers should all measure the same speed for light, no matter how they were moving.
This required abandoning the idea that there is a universal quantity called time that all clocks measure. Instead, everyone would have his own personal time. The clocks of two people would agree if they were at rest with respect to each other but not if they were moving. This has been confirmed by a number of experiments, including one in which an extremely accurate timepiece was flown around the world and then compared with one that had stayed in place. If you wanted to live longer, you could keep flying to the east so the speed of the plane added to the earth's rotation. However, the tiny fraction of a second you gained would be more than offset by eating airline meals.

NumberTenOx

As to why inflation stopped, this is from Guth's "The Inflationary Universe":

"Since the supercooled false vacuum state is not stable, the exponential expansion would not continue forever. Eventually the false vacuum would decay by quantum tunneling."

I won't tell you that I understand this. But the idea that I get is that the Higgs field that is causing inflation is in a state that is metastable, like a coin that is on it's edge. By random chance it will fall out of this state into a more stable state: the real vacuum that we know as space. When this happens somewhere, the effect starts spreading at the speed of light. Eventually, bubbles of this type merge and we get a region of space that is our universe.

Can space expand faster than the speed of light? Take two points in the false vacuum that is inflating. Between these two points space, energy, and gravity are being created at an exponential rate. These two points will soon be moving apart at much faster than the speed of light, even though neither point is really "moving".

The quantum tunneling above can happen many many places at once, quickly turning a large region into real space. How quickly does this happen? Something like 10E-35 seconds, from the start of inflation to the end of decay. I don't understand the issue of time measurement raised elsewhere in this thread. I don't think a time interval that short has anything to do with human perception.

Also remember that light didn't start traveling through the universe until it cooled down enough so that atoms formed, an estimated 300,000 years. Before that the ionized particles would absorb and reemit the light so often that it couldn't travel very far. Once neutral atoms were made they stopped interfering with the light and it's been traveling ever since.

Inflation may or may not be true. But it's so cool because it explains so much about the universe, including how energy, space, and gravity can be related in a way that they can be created from each other.

With inflation we don't need a god that can create the entire universe. We just need an explanation as to where the small amount of Higgs field that started it all came from. Logically this is not a different question, but the quality of this question is dramatically different.