Freethought & Rationalism Archive

GPLindsey · 07-06-2002, 05:51 AM

Kenny's posts make sense to me in regards to another question I had about light--if light can be slowed down in some medium, say to 38mph, and then exits that medium and enters a vacuum, does it continue to travel at 38mph or would it return to the full speed of light?

If light were like other physical matter, say an asteroid passing through a dense gas cloud, it would not speed up again when it exited the cloud. The asteroid would need some energy source to begin accelerating again, because of the loss of momentum.

However with light, if what exits the cloud is just the light reemitted by essentially the last atoms in the cloud, then it would make sense that it would return to travelling the speed of light when it goes back into a vacuum. Do I have this right, Kenny?

If this isn't right, then what would make light return to the speed of light upon entering a vacuum, after it has been slowed down in a medium to a speed of 38mph or some other figure?

Kenny · 07-06-2002, 09:16 AM

Quote:

Originally posted by GPLindsey:
[QB]Kenny's posts make sense to me in regards to another question I had about light--if light can be slowed down in some medium, say to 38mph, and then exits that medium and enters a vacuum, does it continue to travel at 38mph or would it return to the full speed of light?

If light were like other physical matter, say an asteroid passing through a dense gas cloud, it would not speed up again when it exited the cloud. The asteroid would need some energy source to begin accelerating again, because of the loss of momentum.

However with light, if what exits the cloud is just the light reemitted by essentially the last atoms in the cloud, then it would make sense that it would return to travelling the speed of light when it goes back into a vacuum. Do I have this right, Kenny?

Yes, with the comments regarding the necessity of paying attention to the wave-nature of light to understand the full range of propagation effects duly noted. Light in a vacuum must travel at c; that is incontrovertible.

God Bless,
Kenny

beausoleil · 07-06-2002, 09:44 AM

Quote:

Originally posted by Kenny:
<strong>

Yes, with the comments regarding the necessity of paying attention to the wave-nature of light to understand the full range of propagation effects duly noted. Light in a vacuum must travel at c; that is incontrovertible.

God Bless,
Kenny</strong>

One might even say 'definitive'

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07-06-2002, 05:51 AM	#41
GPLindsey Regular Member Join Date: Dec 2001 Posts: 221	Kenny's posts make sense to me in regards to another question I had about light--if light can be slowed down in some medium, say to 38mph, and then exits that medium and enters a vacuum, does it continue to travel at 38mph or would it return to the full speed of light? If light were like other physical matter, say an asteroid passing through a dense gas cloud, it would not speed up again when it exited the cloud. The asteroid would need some energy source to begin accelerating again, because of the loss of momentum. However with light, if what exits the cloud is just the light reemitted by essentially the last atoms in the cloud, then it would make sense that it would return to travelling the speed of light when it goes back into a vacuum. Do I have this right, Kenny? If this isn't right, then what would make light return to the speed of light upon entering a vacuum, after it has been slowed down in a medium to a speed of 38mph or some other figure?

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