Need Lesson on Physics/Relativity

Superman · 10-29-2009, 08:18 AM

Scientists are reporting something exciting today. Gamma Ray bursts have allowed them to see the most distant object ever viewed in the Universe. A star exploded, spewing gamma rays, and that explosion is said to have occurred 13 billion light-years away. Scientists are also saying that this explosion occurred when the Universe was only 600 million years old.

Well, if matter cannot travel faster than the speed of light, then how did two objects (Earth and this exploding star) become 13 billion light-years apart in a period of only 600 million years?

Hugh R · 10-29-2009, 08:24 AM

If I read what you wrote correctly that would imply that the Universe is believed to be 13 Billion + 600 million years old

island911 · 10-29-2009, 08:32 AM

Admit it, Superman ... you're just confused (again) about which way to fly around the world, to turn back time.

Rick Lee · Rick Lee's Garage

They weren't that far apart 13 billion years ago. In fact, the Earth wasn't formed for several billion more years.

MotoSook · 10-29-2009, 08:38 AM

Worm hole.

RKC · 10-29-2009, 08:39 AM

I'm no expert, but if both the star and the Earth were moving away from each other at some % of the speed of light all that time, wouldn't it make sense?

In the same way that the sound from a car's horn blowing, once you've already passed that other car going the opposite way down the highway, wouldn't be heard at the expected, let's say, 1 second delay. This would be because even though you were 343 meters away from the car when the horn blew, by the time the sound catches up to you you are some distance greater than 343 meters away....

Add a great deal of speed to that thought, and it seems to make sense - just as that horn would play minutes later if you were traveling at 342 meters/sec.

KaptKaos · 10-29-2009, 08:40 AM

It also assumes that the universe started at a center and is expanding outward. Thereby placing the earth and this star that exploded 13 billion years ago much closer together.

As Hugh said, the "age" of the universe is really the question.

ckissick · 10-29-2009, 09:10 AM

The big bang was about 13.7 billion years ago. I suppose the star that they're talking about was 600 million years old, meaning it formed about 100 million years after the big bang. It took a long time before things cooled down enough to allow hydrogen to even form. This star formed early, and then exploded at a very young age. The larger the star, the shorter its lifespan.

As the universe expanded, this old star moved away from our region of space . When the Gamma Ray Burst occurred 13 billion years ago, the star was much closer to our region, and you'd think the light would have reached us billions of years ago. After all, the speed of light is constant, no matter what the relative velocities are of the object emitting the light, and the observer.

However, because the universe is expanding, it took longer for the light to get here because it has ever longer distances to travel as the universe continues to expand. It's like catching up to a speeding train. There is a threshold distance beyond which we cannot see into the past. We can't see back to the Big Bang because the light from it has not caught up to us yet, and it never will. The outermost regions of space are moving away from us at a rate greater than the speed of light.

Rick Lee · Rick Lee's Garage

Bottom line is that when we get hit with a gamma ray burst, there will be no warning, since it travels at the speed of light, and it will be all over for us when it hits.

Gogar · 10-29-2009, 09:52 AM

They weren't 13 billion light years away from each other when the explosion happened,

They are 13 billion light years away now.

You need to include the concept that the Earth and the the star that exploded are moving away from each other most of the time. Like, "Light-time doppler effect."

cgarr · cgarr's Garage

Maybe is just a big continuous loop of tape?

The Gaijin · 10-29-2009, 10:06 AM

As we all know, kryptonite is formed by gamma rays.

Supe Man - you had better get back to that fortress of solitude.

Rick Lee · Rick Lee's Garage

Quote:

Originally Posted by Gogar

They weren't 13 billion light years away from each other when the explosion happened,

They are 13 billion light years away now.

You need to include the concept that the Earth and the the star that exploded are moving away from each other most of the time. Like, "Light-time doppler effect."

The Earth was billions of years from even being formed when the explosion happened.

Pazuzu · 10-29-2009, 12:45 PM

I was researching gamma ray bursts in my previous career.

I'm not going to try to explain the expansionary universe here, I just wanted to toss that snippet out

Sammy will come by any second now and tell you that science is evil and lies and steals his lunch money, so why bother asking such questions in the first place?

island911 · 10-29-2009, 12:47 PM

Quote:

Originally Posted by Pazuzu

...

I'm not going to try to explain the expansionary universe here, ..

'cuz ya can't

Pazuzu · 10-29-2009, 01:06 PM

Quote:

Originally Posted by island911

'cuz ya can't

Why not? Lack of time, lack of knowledge, or lack of truth?

Bill Verburg · Bill Verburg's Garage

conventional matter cannot travel faster than light speed but the expansion of the universe itself, ie the expansion of space time can and has proceded faster than the speed of light, that is if inflation as described in the standard models is correct

Pazuzu · 10-29-2009, 01:57 PM

Quote:

Originally Posted by Bill Verburg

conventional matter cannot travel faster than light speed but the expansion of the universe itself, ie the expansion of space time can and has proceded faster than the speed of light, that is if inflation as described in the standard models is correct

Correct, and in the process it decoupled information transfer between any two points that separated faster than the speed of light. What that means in those two points in space can never know what is happening at the other one, since they are farther apart than light could travel in the age of the universe. Our "visible" universe is the sphere of space that is within 13.6 million light years. We do not know and cannot know how much larger space actually is outside that bubble.

Superman · 10-30-2009, 11:19 AM

Quote:

Originally Posted by Pazuzu

Correct, and in the process it decoupled information transfer between any two points that separated faster than the speed of light. What that means in those two points in space can never know what is happening at the other one, since they are farther apart than light could travel in the age of the universe. Our "visible" universe is the sphere of space that is within 13.6 million light years. We do not know and cannot know how much larger space actually is outside that bubble.

This is interesting, and illustrates my quandry. How can two objects, which are "within" each others' perceivable Universe, become 13B light years distant in a span of 600M years? Perhaps the Earth and the exploding star have been receding from one another at a rate approaching light speed, causing the light from the star to be coming toward us at far less than light speed due to a Doppler Effect. And yet.....that defies the principle that light travels at......light speed.

I have a headache.

Pazuzu · 10-30-2009, 11:52 AM

Quote:

Originally Posted by Superman

This is interesting, and illustrates my quandry. How can two objects, which are "within" each others' perceivable Universe, become 13B light years distant in a span of 600M years? Perhaps the Earth and the exploding star have been receding from one another at a rate approaching light speed, causing the light from the star to be coming toward us at far less than light speed due to a Doppler Effect. And yet.....that defies the principle that light travels at......light speed.

I have a headache.

You're misreading things. The star formed and exploded 600 million years after the big Bang, which is the same as saying 13 billion years ago. It was never near us, and it hasn't traveled away from us. As was stated, it was LONG gone before the Earth (heck, before the Milky Way galaxy!) was even a twinkle in daddy's eyes.

Don't worry about the expansion of the Universe for this scenario, it's not particularly important, and it'll just give you headaches

What's important is that it's taken this long for the light to reach us (13 billion years), and therefore, this is one of the most distant stars we've seen. The more distant it is, the older it is (since it took 13 billion years to reach us). The older it is, the closer to the beginning it was. The closer to the beginning, the more likely it was made of primordial materials (close to the original 75% hydrogen, 25% helium, and nothing else). We need to verify those percentages in the very early universe to give support to both the Big Bang theory, and atomic theory that calculated the formation of those first building blocks.