# Speed of light and absolute zero
**URL:** https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785
**Category:** Factual Questions
**Created:** [June 28, 2007, 4:38pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785 "2007-06-28T16:38:18Z")
**Posts on this page:** 15
**Page:** 1
### Author:  [@sweeteviljesus](https://boards.straightdope.com/u/sweeteviljesus)
#### Post date: [June 28, 2007, 4:38pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/1 "2007-06-28T16:38:18Z")
My dad was saying something the other day about the relationship between the speed of light and absolute zero. I am confident he didn’t have his facts right, but IIRC, there is some way in which they are related. Can the usual suspects enlighten me?
Thanks,
Rob
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [June 28, 2007, 4:52pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/2 "2007-06-28T16:52:27Z")
Likely your dad heard something about the effect of Bose Einstein condensates on the speed of light:
[Physicists Slow Speed of Light](http://www.hno.harvard.edu/gazette/1999/02.18/light.html)
> [@](#):
>
> Light, which normally travels the 240,000 miles from the Moon to Earth in less than two seconds, has been slowed to the speed of a minivan in rush-hour traffic – 38 miles an hour.
>
> An entirely new state of matter, first observed four years ago, has made this possible. When atoms become packed super-closely together at super-low temperatures and super-high vacuum, they lose their identity as individual particles and act like a single super- atom with characteristics similar to a laser.
>
> Such an exotic medium can be engineered to slow a light beam 20 million-fold from 186,282 miles a second to a pokey 38 miles an hour.
The cite’s from 1999, when physicists first started reporting the effect. Since then, other tricks have been played on the lowly photon: [Light Changed to Matter, Then Stopped and Moved](http://www.photonics.com/content/news/2007/February/8/86331.aspx)
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### Author:  [@Grey](https://boards.straightdope.com/u/Grey)
#### Post date: [June 28, 2007, 5:07pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/3 "2007-06-28T17:07:55Z")
It should be noted that any kind of matter slows down light. Cherenkov radiation (when charged particles move faster through matter than photons) is a neat example of this.
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### Author:  [@Psycho\_Originals](https://boards.straightdope.com/u/Psycho_Originals)
#### Post date: [June 28, 2007, 5:17pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/4 "2007-06-28T17:17:20Z")
I saw on [www.livescience.com](http://www.livescience.com) last year that scientists have actually made light go in reverse. I didnt understand the physics of it at all, hopefully someone can find this article, because i have not been able to find anything.
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### Author:  [@FatBaldGuy](https://boards.straightdope.com/u/FatBaldGuy)
#### Post date: [June 28, 2007, 7:55pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/5 "2007-06-28T19:55:49Z")
[QUOTE=Psycho Originals]
I saw on [www.livescience.com](http://www.livescience.com) last year that scientists have actually made light go in reverse.
[/QUOTE]
Heck, that’s easy to do. Just hold up a mirror.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [June 28, 2007, 8:38pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/6 "2007-06-28T20:38:19Z")
> [@](#):
>
> I saw on [www.livescience.com](http://www.livescience.com) last year that scientists have actually made light go in reverse. I didnt understand the physics of it at all, hopefully someone can find this article, because i have not been able to find anything.
Nothing too fancy there. Once you get the trick of slowing light down to 38 mph or 15 mph or whatever, you just put the whole apparatus on a truck driving in the other direction at a faster speed.
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### Author:  [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)
#### Post date: [June 28, 2007, 8:50pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/7 "2007-06-28T20:50:15Z")
[QUOTE=Chronos]
Nothing too fancy there. Once you get the trick of slowing light down to 38 mph or 15 mph or whatever, you just put the whole apparatus on a truck driving in the other direction at a faster speed.
[/QUOTE]
Oh, sure, it’s going in reverse in _your_ reference frame, but it’s still going forward relative to the guy in the truck.
Or something. 😉
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### Author:  [@OldGuy](https://boards.straightdope.com/u/OldGuy)
#### Post date: [June 29, 2007, 2:42am UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/8 "2007-06-29T02:42:14Z")
[QUOTE=Squink]
An entirely new state of matter, first observed four years ago, has made this possible. When atoms become packed super-closely together at super-low temperatures and super-high vacuum, they lose their identity as individual particles and act like a single super- atom with characteristics similar to a laser.
[/QUOTE]
Just how do you pack atoms closely together in a vacuum? A vacuum is the absence of any atoms (or particles) at all.
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [June 29, 2007, 3:09am UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/9 "2007-06-29T03:09:28Z")
By vacuum, they mean that there’s nothing in there _besides_ their closely packed array of sodium atoms.
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [June 29, 2007, 7:30am UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/10 "2007-06-29T07:30:54Z")
[QUOTE=Chronos]
Nothing too fancy there. Once you get the trick of slowing light down to 38 mph or 15 mph or whatever, you just put the whole apparatus on a truck driving in the other direction at a faster speed.
[/QUOTE]
Is this a whoosh? Isn’t the speed of light independent of reference frame? Or does that only count when it’s going full whack?
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### Author:  [@Liberal](https://boards.straightdope.com/u/Liberal)
#### Post date: [June 29, 2007, 10:41am UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/11 "2007-06-29T10:41:42Z")
[QUOTE=Mangetout]
Is this a whoosh? Isn’t the speed of light independent of reference frame? Or does that only count when it’s going full whack?
[/QUOTE]
I believe it applies only to the speed of light in vacuum. At least, Einsteins first premise was that the speed of light is constant _in a vacuum_.
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### Author:  [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)
#### Post date: [June 29, 2007, 1:32pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/12 "2007-06-29T13:32:19Z")
[QUOTE=Mangetout]
Is this a whoosh? Isn’t the speed of light independent of reference frame? Or does that only count when it’s going full whack?
[/QUOTE]
c is the speed of light in a vacuum and is the maximum rate that light, or anything else, can have. Electro magnetic waves such as light travel slower in a medium such as glass or air or water.
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### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [June 29, 2007, 2:13pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/13 "2007-06-29T14:13:47Z")
I understand that, but it’s the relativistic aspects I don’t get - if we have light travelling at, say, 0.75c in water and I am travelling at 0.75c in the opposite direction towards it (ignoring for a moment that such velocity would be rather difficult for a physical object in water), do I observe the light as incoming at a greater velocity than c?
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [June 29, 2007, 8:17pm UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/14 "2007-06-29T20:17:56Z")
> [@](#):
>
> if we have light travelling at, say, 0.75c in water and I am travelling at 0.75c in the opposite direction towards it (ignoring for a moment that such velocity would be rather difficult for a physical object in water), do I observe the light as incoming at a greater velocity than c?
No. Light moving at .75c relative to water behaves the same way as anything else moving at .75c relative to water, and in no case will your velocity ever be greater than c relative to anything.
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### Author:  [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)
#### Post date: [June 30, 2007, 2:53am UTC](https://boards.straightdope.com/t/speed-of-light-and-absolute-zero/409785/15 "2007-06-30T02:53:45Z")
[QUOTE=sweeteviljesus]
My dad was saying something the other day about the relationship between the speed of light and absolute zero. I am confident he didn’t have his facts right, but IIRC, there is some way in which they are related. Can the usual suspects enlighten me?
[/QUOTE]
I often hear them compared because neither can be reached, only approached. You can’t ever accelerate to lightspeed, nor can you chill something to absolute zero.