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How far does light travel?


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Showing 1-25 of 225 posts in this discussion
Initial post: Sep 24, 2011 3:25:39 PM PDT
chasmcg says:
How far does light travel before it dies? It doesn't seem to die since we're looking billions of years into the past. Also, if scientists claim to see leftovers from the 'big bang', how can this be? Wouldn't the light from the 'bb' have passed the earth long ago? Thanks.

In reply to an earlier post on Sep 24, 2011 4:43:31 PM PDT
noman says:
Cosmology FAQ
http://www.astro.ucla.edu/~wright/cosmology_faq.html

In reply to an earlier post on Jul 12, 2012 2:36:04 PM PDT
Charlie T. says:
Forever.

Posted on Jul 12, 2012 2:55:15 PM PDT
Julian says:
Light can potentially go on forever but dust, gasses, and other objects can get in the way and stop it.

Posted on Jul 12, 2012 3:21:40 PM PDT
Last edited by the author on Jul 12, 2012 3:22:40 PM PDT
According to the Inflationary Big Bang theory, the universe can grow faster than the speed of light. (Space itself can expand at any rate required, since it isn't subject to Einstein's law about the speed of light barrier.)

However, this expansion apparently has the property that it can go faster in certain eras than others. We happen to be in a slow era, and so the light from the BB is just catching up to us, now. (We are like the hare in the tortoise/hare fable--and light is like the tortoise.)

Hope this helps.

In reply to an earlier post on Jul 12, 2012 5:40:47 PM PDT
The Weasel says:
I don't think the leftovers from the big-bang specifically refer to light that we can now see as having been generated at the time of the big-bang.

However, since we can "see" into the past when observing light from far off we do gain some understanding of the past state of the universe when compared to what we observe from closer in time when looking at objects nearer to us.

By projecting our observations backwards we can hypothosize about the state of the universe before our ability to observe it. Okay, that's over simplified, but I'm not a scientist.

Hope that helps a little.

In reply to an earlier post on Jul 12, 2012 6:00:24 PM PDT
chasmcg wrote:
"How far does light travel before it dies? It doesn't seem to die since we're looking billions of years into the past. "
================================
You are rocking the boat harsher than you think.

Because, had light been waves, it should flatten out due to the red-shifting and the alleged expansion of the universe. Waves do not travel indefinitely unless energized to keep going. The same could be said on EM waves which definitely share the space with plenty of company.

Had light been particles, it is even harder to imagine that particles could travel indefinitely without losing their identity.

But, our distilled sciences deal with measurable variables, while remote traveling light falls outside our ability to detect or ascertain.

Mohamed F. El-Hewie

In reply to an earlier post on Jul 12, 2012 8:38:12 PM PDT
barbW says:
We can 'see' a planet that's been reliably calculated to be 12.7 billion years old.

In reply to an earlier post on Jul 12, 2012 8:54:11 PM PDT
does not die
goes forever until it hits something that stops it

how high is up
how big is the universe

In reply to an earlier post on Jul 12, 2012 8:55:06 PM PDT
wrong again

In reply to an earlier post on Jul 12, 2012 9:13:12 PM PDT
What is actually seen in the CMBR pictures is a time 380,000 years "post bang", when the expanding ionized plasma finally cooled off enough to see through. This event is called "photon decoupling". Prior to this, the situation was similar to what's inside a fluorescent lightbulb, which is hard to see through, because the charged ions inside scatter the photons. It does not appear to be in the cards to see further back than this, using photons. Maybe if we could build a "neutrino telescope", we could see further back.

In reply to an earlier post on Jul 12, 2012 11:36:36 PM PDT
Re OP: Light doesn't "die": it can go from one end of the universe to the other (speaking metaphorically, of course -- the universe doesn't have "ends".) The reason that we can see light from the big bang (actually, cosmic background radiation, which isn't really light) is because the universe has been expanding.

Posted on Jul 13, 2012 4:19:48 AM PDT
Yo says:
very, very far

In reply to an earlier post on Jul 13, 2012 5:34:25 AM PDT
Last edited by the author on Jul 13, 2012 8:58:10 AM PDT
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In reply to an earlier post on Jul 13, 2012 8:31:20 AM PDT
Last edited by the author on Jul 13, 2012 8:32:35 AM PDT
It travels one light second every second, one light minute every minute, one light day every day, one light week every week, one light month every month, one light year every year, etc.

A basic tenet of physics thanks to Einstein is that light travels at the same velocity (one light second per second, etc) in empty space in all inertial reference frames regardless of the velocity of its source.

Photons are stable particles, therefore they don't spontaneously "die". They exist until an interaction occurs in which they are absorbed by a charged particle. Absent such an interaction, their lifetime is infinite.

In reply to an earlier post on Jul 13, 2012 10:28:17 AM PDT
so that book lied
about the restaurant at the end of the universe

In reply to an earlier post on Jul 13, 2012 12:10:23 PM PDT
Yeah, just like the Bible lied about the "four corners of the earth" (Revelation 7:1).

In reply to an earlier post on Jul 13, 2012 12:14:22 PM PDT
hmmm..........

not sure which side you are takin g

Posted on Jul 13, 2012 12:43:32 PM PDT
D. Vicks says:
So did A+ Einstein know about FTL speed using a wormhole?

And if your going at FTL how do you slow down?

In reply to an earlier post on Jul 13, 2012 7:01:45 PM PDT
Doctor Who says:
you cant make an FTL drive. Stargate U lied.

The "hyperdrives" are actually much more realistic, as they leave "normal" space.

When you travel through a wormhole you maintain a velocity < c, you just take a shortcut. The best visual for this might just be Stargate SG1 or Stargate Atlantis when a ship opens a "hyperspace window" they fly into it at their normal sublight speed. They continue at this low speed until they exit "hyperspace" at which point the they arrive at the same slow speed. They appear to speed up for the camera because A) its a TV show, and B) because the space they are traversing is distorted relative to the camera. The person on the ship would feel no change between normal space and hyperspace as the ship still travels at the same speed. They also don't travel very far. They just take a short cut. The shortest distance between two points might be a line that is 200 ly long, but if you create a wormhole you might be able to traverse the same distance by taking a path that is only a few meters long. They key idea here is that you would not be going faster than the speed of light. You would essentially leave the 3 dimensional universe and go "up".

In reply to an earlier post on Jul 13, 2012 9:45:21 PM PDT
barbW says:
The planet is in M4, about 7200 light years away from us, so you're making the wrong assumptions.

In reply to an earlier post on Jul 13, 2012 10:20:42 PM PDT
http://en.wikipedia.org/wiki/PSR_B1620-26

In reply to an earlier post on Jul 13, 2012 10:26:14 PM PDT
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In reply to an earlier post on Jul 13, 2012 10:42:53 PM PDT
Although I notice that PSR_B1620-26 is reported to be 12400 light-years away, making the "in M4" idea a bit odd. It's 70% further away than M4 is. It _is_ in the direction of M4, and presumably had some history in common with M4 billions of years ago.

In reply to an earlier post on Jul 13, 2012 10:52:03 PM PDT
Last edited by the author on Jul 13, 2012 11:05:18 PM PDT
Read the link. Then read werranth's post again.

The two are reasonably consistent with each other. werranth is claiming that the AGE of the planet is 12.7 billion years, and claiming (indirectly) that it's DISTANCE is 7200 LY, on the assumption that it is "in M4". The actual distance appears to be more like 12400 LY, which is only 70% different. Your faulty INTERPRETATION of w's remarks, however, is wildly off, and by a much larger factor. Like about a million, or so.

PS.
Just so you know, my first impression was exactly like yours, in that I thought werranth must have been confusing the age due to distance with the actual age. Unlike you, however, I actually looked it up, and found out that werranth was essentially correct, BEFORE spouting off.

PPS.
It is best to condescend from a position of correctness. When you do it based on erroneous assumptions or misreads, it makes you appear foolish.
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Discussion in:  Science forum
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Initial post:  Sep 24, 2011
Latest post:  Nov 12, 2012

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