nature of light?

Question

we know that when somethin travels at the speed of light so many changes start to take place.... things like length contraction, time dilation etc.
And if i traveled by you at the speed of light u wouldnt even notice;.....

I was just wondering that light is made of photons..... and these photons travel at speed c. And we all have a feeling for what light 'looks like' .
what would we observe if light traveled at a lower speed? say just about 20% speed c !
Would the nature of photons change? Would light be something different?

Answer 1

The thing is, photons are massless. A massless particle can carry energy and momentum only if it travels at the speed of light. So if a photon slowed down, it would need to have mass (making it something quite different) or it wouldn't exist at all. If the photon had mass, that would dramatically change the electromagnetic interaction. E-M interactions wouldn't have practically infinite range; they would cut off like the strong and weak interactions do. If the cutoff were smaller than the atomic scale, chemistry would be way different (or practically cease to exist). If the cutoff were larger, it might effect larger-scale E&M reactions.

Answer 2

If you want an amusing answer, look at the Terry Prachett Diskworld science fiction novels. These start with the idea that the old Earth belief that the earth was flat and rode on the backs of elephants standing on a turtle really is true. There is magic and so forth.
So if the world is flat, how does dawn arrive. Well, the logical answer is "Instantly, everywhere", but as much as possible, Terry keeps the effects the same as on Earth. So the sun arrives progressively in Diskworld (across time zones) because light moves slowly! So in various books, people on a mountain see the light progressing across the plain, people riding a broom stick catch up with the moving light (and start to crash) and other odd ball effects.
In the Elizabeth Moon book, Once A Hero, a group of people are crossing the outside of a large mobile repair station when it is taken into FTL (faster than light) flight mode. The description of light's behavior as they walk along the hull includes a beam of a headlight making snakey loops as the head is moved, light coming out of a repair bay looking like smoke, and views taking on a red or blue tinge as the head is turned from side to side. All speculation, since we have no FTL drive to test it on.

Answer 3

u can't travel to me with speed of light my boy until einstein's eqn. is discarded by scientists
u will have infinite mass if ur speed equals that of light which is not possible
and as far as ur Ques. is concerned photon is never mention as object anywhere which can variable speed as we do
in einstein's photometric equation it is clearly mentioned that photon can't speed less than 'c' , no matter whatever the frequency or intensity
even relative velocity of photon is taken yo be 'c' so there is no questin of even assuming that photon will have speed less than c
photon id massless entity which just have energy and momentum ,

Answer 4

And if i travelled by you at the speed of light u wouldn't even notice;.....
Answer: You, being a material body, simply cannot travel at the speed of light by the Einstein's Special theory of Relativity.

Rest of the question is not clear.

Answer 5

Light has been slowed down, if you didn't already know. It looks like just some beam frozen. It required some form of supercooling in a gas to slow light down to a crawl.