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Junior
Joined: 18 Nov 2005
Location: the eye
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 Posted: Sun Apr 29, 2012 6:00 pm Post subject: |
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| leicsmac wrote: |
If I may interject here...this is sort of my territory.
Some objects are indeed moving away from us at a relative (and that's the important term here) speed that is faster than lightspeed.... |
Not sure what you mean by "relative"...
The universe expands faster than the speed of light.
Some of the galaxies we see right now are moving away from us faster than the speed of light.
http://curious.astro.cornell.edu/question.php?number=575
What these guys on here have failed to recognize is that space is a vacuum, lol.
If you want to state that nothing can exceed lightspeed while it is within the earths atmosphere, then yes, I'd agree with you.
But its the implications of lightspeed in space that interest me.
If we could travel with a ray of light that is now at the furthest reaches of our universe, one initially emitted from the big bang, then no time would have passed.
A thousand, a million years might pass on the earth, but on that ray of light..no time would have elapsed.
time is relative depending on your refernece point. The earth could easily have been created in 6 days, depending on where you are looking at it from.
Last edited by Junior on Sun Apr 29, 2012 6:13 pm; edited 1 time in total |
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leicsmac
Joined: 07 Jul 2010
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| Posted: Sun Apr 29, 2012 6:03 pm Post subject: |
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| Junior wrote: |
| leicsmac wrote: |
If I may interject here...this is sort of my territory.
Some objects are indeed moving away from us at a relative (and that's the important term here) speed that is faster than lightspeed.... |
Thankyou. Exactly.
The universe expands faster than the speed of light.
Some of the galaxies we see right now are moving away from us faster than the speed of light. |
Not quite Junior....that's the whole point - we can't see them, because the radiation they emit will never reach us for observation. But we have a pretty good idea (through secondary information) that they're out there. |
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Junior
Joined: 18 Nov 2005
Location: the eye
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| Posted: Sun Apr 29, 2012 6:18 pm Post subject: |
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| leicsmac wrote: |
Not quite Junior....that's the whole point - we can't see them, because the radiation they emit will never reach us for observation. But we have a pretty good idea (through secondary information) that they're out there. |
Read the link I posted..
| Quote: |
Since we know that the speed of light is around 300,000 kilometers per second, it is easy to calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light. The answer we get is that the two galaxies must be separated by around 4,200 megaparsecs (130,000,000,000,000,000,000,000 kilometers).
if you use a value of around 1.4 for z (the redshift), you get the required distance of 4,200 megaparsecs. Therefore, any galaxy with a redshift greater than 1.4 is currently moving away from us faster than the speed of light.
Can we see these galaxies? Yes, we certainly can! Bright galaxies are regularly detected out to redshifts of a few; a redshift of 1.4 isn't really that much. For example, here are some pictures of quasars (galaxies with extremely active black holes in their centers) with redshifts around 5. We can even see light (although not individual objects) all the way back to a redshift of 1000 or so. |
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leicsmac
Joined: 07 Jul 2010
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| Posted: Sun Apr 29, 2012 6:48 pm Post subject: |
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| Junior wrote: |
| leicsmac wrote: |
If I may interject here...this is sort of my territory.
Some objects are indeed moving away from us at a relative (and that's the important term here) speed that is faster than lightspeed.... |
Not sure what you mean by "relative"...
The universe expands faster than the speed of light.
Some of the galaxies we see right now are moving away from us faster than the speed of light.
http://curious.astro.cornell.edu/question.php?number=575
1.) What these guys on here have failed to recognize is that space is a vacuum, lol.
If you want to state that nothing can exceed lightspeed while it is within the earths atmosphere, then yes, I'd agree with you.
But its the implications of lightspeed in space that interest me.
If we could travel with a ray of light that is now at the furthest reaches of our universe, one initially emitted from the big bang, then no time would have passed.
A thousand, a million years might pass on the earth, but on that ray of light..no time would have elapsed.
2.) time is relative depending on your refernece point. The earth could easily have been created in 6 days, depending on where you are looking at it from. |
Numbers are mine for reference.
1.) The difference between the speed of light in a gas atmosphere and in a vacuum is actually very small. It's all to do with the refractive index of the medium (formula is refractive index = speed of light in vacuum/speed of light through medium). So we know to a certainty that the speed of light in a vacuum is 299,792,458 m/s (taken from satellite data exchanges) and the speed of light in Earth's atmosphere is about 90 m/s slower than this.
2.) You're actually not too far off with this one. Of course, all of the units we used to measure distance and time are entirely arbitrary and manmade...all distance and time is measured relative to something else. From the view of a human, the Universe has existed for around 13.7 billion years). From the view of a 'different' being...it could be anything. Could have been 6 days. [/b] |
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Underwaterbob
Joined: 08 Jan 2005
Location: In Cognito
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| Posted: Wed May 02, 2012 4:43 pm Post subject: |
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| Junior wrote: |
| leicsmac wrote: |
Not quite Junior....that's the whole point - we can't see them, because the radiation they emit will never reach us for observation. But we have a pretty good idea (through secondary information) that they're out there. |
Read the link I posted..
| Quote: |
Since we know that the speed of light is around 300,000 kilometers per second, it is easy to calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light. The answer we get is that the two galaxies must be separated by around 4,200 megaparsecs (130,000,000,000,000,000,000,000 kilometers).
if you use a value of around 1.4 for z (the redshift), you get the required distance of 4,200 megaparsecs. Therefore, any galaxy with a redshift greater than 1.4 is currently moving away from us faster than the speed of light.
Can we see these galaxies? Yes, we certainly can! Bright galaxies are regularly detected out to redshifts of a few; a redshift of 1.4 isn't really that much. For example, here are some pictures of quasars (galaxies with extremely active black holes in their centers) with redshifts around 5. We can even see light (although not individual objects) all the way back to a redshift of 1000 or so. |
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You left out this part:
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| You might be wondering how we could possibly see a galaxy that is moving away from us faster than the speed of light! The answer is that the motion of the galaxy now has no effect whatsoever on the light that it emitted billions of years ago. The light doesn't care what the galaxy is doing; it just cares about the stretching of space between its current location and us. So we can easily imagine a situation where the galaxy was not moving faster than the speed of light at the moment the light was emitted; therefore, the light was able to "outrun" the expansion of space and move towards us, while the galaxy moved away from us as the universe expanded. Keeping in mind what we learned above -- that farther objects recede faster in a proportionally stretching universe -- we can immediately see that right after the light is emitted, the galaxy is moving away from us faster than the point at which the light is located, and that this disparity will only increase as time goes on and the galaxy and light separate even more. Therefore, we can easily have a situation where the galaxy keeps on moving away faster and faster, eventually reaching or exceeding the speed of light relative to us, while the light which it emitted billions of years ago leisurely coasts on, never having to move across a region of space that was stretching faster than the speed of light, and therefore reaches us eventually. |
So while yes, we can see light from galaxies moving relatively faster than the speed of light away from us, it does not prove that anything moves faster than the speed of light.
Relative velocities are not absolute velocities.
The bigger challenge to the speed of light as a universal constant would be something like quantum entanglement or superposition, but we've known about that stuff for years now and nothing seems to be coming of it. |
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