Light so fast it goes backwards

[Bluemofia]

Ive actually heard of Cherenkov radiation, I just didnt know what it was, thanks. BTW, so what happpens to time while light is going backward or slowing down?

Slowing down, c is still c.

It's just that the light is being absorbed by atoms, held temporarily, and re-released. Thus, the speed of light going through that medium would appear slower. Time would flow normally, because the maximum speed limit is still c.

Or take this example:

Light enters water at c. It impacts the first atom at c. Then it is held for a while, and released at c. Then it goes to the next atom at c. And it repeats.

The speed of light is still c, just that it is constantly stopping and going.

 

[VoodooAce]

Quantum physics is to hard to understand. Just accept what you read. BTW it could be possible. time is screwy at the speed of light nothing realy is normal.

Time is screwy, period. It just appears normal and constant to us. I don't understand it, I just know it.

Also, someone asked earlier about the speed of light being the unbreakable and all. But things happen all the time in quantum physics that break that law....so apparently its not a black and white law.

 

[Cheezy the Wiz]

ok either truronian or mise messed up and confused me, because thats a lambda symbol, not a gamma.

great now i dont get it any more

 

[Mise]

ok either truronian or mise messed up and confused me, because thats a lambda symbol, not a gamma.

great now i dont get it any more

The lorentz factor is given the gamma symbol, not lamda.

 

[JohnRM]

Think about it this way. You can see, because light is produced from various sources and it reflects off of objects. The images you see are light energy registering in your brain to form the image of what it is that the light was reflecting off of. If you made light that originated from yourself move backward and return, you would see an image of yourself. Understand?

 

[Bozo Erectus]

Has anyone been able to make light go faster, not just slow it down or go backwards?

 

[Mise]

Has anyone been able to make light go faster, not just slow it down or go backwards?

Yup, by the process that hassan_lembeck described on the previous page.

The phase velocity of light also increases in certain plasmas, where the refractive index is less than 1.

 

[Bozo Erectus]

Ok so then this means that the speed of light isnt a physical constant, doesnt it?

edit: it is in a vacuum, ok I think I got it.

 

[Truronian]

The lorentz factor is given the gamma symbol, not lamda.

Yeah, sorry. My teacher can't draw gammas so he used lambda instead. It must have worn of on me

 

[Cuivienen]

Ok so then this means that the speed of light isnt a physical constant, doesnt it?

edit: it is in a vacuum, ok I think I got it.

Exactly. I'm not quite sure how one would go about "speeding up" light, however, at least without relativity. Slowing down is simple; make the substance block (or "hold") the light temporarily. Any mass will slow light because it spends time impacting the mass.

By History_Buff's description, light can only "speed up" due to relativistic activity (in which case it isn't actually moving any faster, it just looks like it).

 

[Bozo Erectus]

Its crazy stuff. Its all way over my head, but I dont know, theres just something fishy about light and time I cant quite put my finger on.

 

[El_Machinae]

The speed of light can't be a constant, because we cannot accurately measure the speed of light. We just pretend it's a constant when the sig. digs. from the Planck length don't matter

 

[warpus]

According to some theories the speed of light has never been constant and has been slowly changing over time..

 

[Truronian]

According to some theories the speed of light has never been constant and has been slowly changing over time..

Yeah, but these theories nearly always end up with the same conclusion, namely that the earth was created in seven days by an omnipotent superbeing.

 

[Erik Mesoy]

The speed of light can't be a constant, because we cannot accurately measure the speed of light. We just pretend it's a constant when the sig. digs. from the Planck length don't matter

By that logic, Pi isn't a constant either, because it always has more digits and we can't accurately measure it. Ridiculous.

 

[Ayatollah So]

According to some theories the speed of light has never been constant and has been slowly changing over time..

You can't pinpoint whether it's the speed of light or another fundamental "constant" that's been changing*, but ... yup. God not only plays dice with the universe, He also changes the rules in the middle of the game.

*Details: the dimensionless number alpha is equal to e^2/hc, where e is the value of the charge on an electron (or a proton), h (more correctly, 'h-cross', the letter h with a line through it) is one way of stating Planck's constant, and c is the speed of light. Alpha has been changing, according to the latest and greatest research. Whether you blame it on e, h, or c is up to you - or not.

 

[El_Machinae]

By that logic, Pi isn't a constant either, because it always has more digits and we can't accurately measure it. Ridiculous.

Pi is a definition, not a measurement. I was handily shown that in the thread I just linked.

OTOH, the velocity of c is a measurement. And such, it's subject to measurement accuracy. Since accuracy has a lower bound, we don't actually know whether it's a constant.

In fact, I'd expect that the speed of light to be slightly variable at utter accuracy ratings.

 

[warpus]

Yeah, but these theories nearly always end up with the same conclusion, namely that the earth was created in seven days by an omnipotent superbeing.

http://www.newscientist.com/article.ns?id=dn6092

 

[blackheart]

http://www.newscientist.com/article.ns?id=dn6092

Then the universe exploded...

 

[Elrohir]

umm.. anybody else feeling stupid while reading this thread? (I know I am)

I felt pretty stupid reading this thread. I think I understand the basic premise, conceptually at least, but I'm having trouble understand the implications, and what everyone else is saying. Ah well, I'm not a math or science guy; I won't be a physicist. I don't need to understand it all.