Why can't light stop moving?

Question

And can light travel in reverse? Not as a result of hitting an object.

Answer 1

Light is not an object, therefore it can't stop moving. It travels is all directions.

Answer 2

Einsteins law E=mc^2 where c is the velocity of light shows you that if the velocity decreases to zero the energy decreases to zero. The other important equation to do with light if E=hf where f is frequency and h a constant, if E goes to zero, the freqency goes to zero, therefore it's not light anymore. Baisicly it doesn't work.
Light can slow down, that's why it bends in water, when you look up the optical properties of a material you can find the speed of light through the material (Refractive index: n).
Now think about this, if light goes in one side of a glass block and slows down, it's energy must decrease from the above equation. But when the same light leaves the glass block it travels at the speed of light in air again (c = 3 x 10^8 m/s), so it's seemingly picked up energy which is impossible as nothing comes for free etc. So what's happened?

This is simple evidence that light interacts with atoms molecules

Answer 3

Ed G is right, light has been stopped experimentally. See his reference, it's also on-line. [See source.]

By traveling "in reverse," I presume you mean towards a source of light. The bean of light would make a sort of U-turn after leaving the source. It would not back up.

In fact, theoretically, it can be made to do a U-turn without "hitting an object." If a gravitational field were strong enough, it could bend light all the way around back to the light's source. This would be a relativistic effect of bending space under extreme gravitational pull. [See source.] As best as we can tell, there is no gravitational pull strong enough to actually do this, but it is possible.

Answer 4

The speed of light is generally taken to be the speed that photons/electomagnetic waves travel through space in a vacuum. If light travels through other media then that speed varies ie slows down. Last year an experiment was carried out where the photons were actually stopped and held in "mid air" (cool or what?). If memory serves me correctly,they carried out this experiment in a liquid with some kind of electro-magnetic field across it. It seems to me that if they can stop light then allow it to move then they can probably dictate the direction it takes, thus it would be a good bet that light can be reversed. :)

Answer 5

Light never stops moving because it has the properties of a wave. It continues in a straight line until it hits something which reflects or absorbs it.

(It also bends slightly when it travels through a gravitational field, however, one way of thinking says that the light is not bending, rather, gravity causes space-time to warp and the light is travelling straight.)

And yes, light can travel in reverse. Just point the flashlight the other way. It keeps moving in whatever direction it is sent... send it the other way and it goes in reverse.

Answer 6

due to the theory of relativity it would take an infinite amount of energy to accelerate a particle (or in this case wave-particle) up to the speed of light, this is also true for the reverse effect of deceleration, this would also take an infinite amount of energy, it is possible to slow light down but not by a great deal. you can stop light (technically this is not really stopping it though, more absorbing it) by blocking its path with a black object. furthermore light cannot simply be reflected from nothing it must caome into contact with something sucjh as a mirror. such faster-than-light particles have been theorised but never seen, because time would move backwards for them.

Answer 7

Hi>
The technical bit :
Light -electromagnetic radiation does not really travel in a straight line. It bends a bit due to gravitational forces.
As for going in reverse, you could, avoiding reflecive stuff, which work, mirrors etc., bung a planet or three in the way.
But that would only bend the path of the photons.
A tricky question., and interesting.

Bob

Answer 8

Since light is an energy wave, if it stops moving then it stops being light. Just like with sound, if the sound wave stops moving then sound doesn't exist. Light travels in all directions at once from its source.

Answer 9

Depends what you mean by light.
Light is part of a continuum of electromagnetic waves of which only a narrow range form what we call visible light. Radio waves are from the same family but we can't see them with our eyes.
So, the short answer is that we can stop visible light actually, for example by shining a beam of light onto a black background where it will be stopped (black absorbes visible light). But what actually happens is the black surface re-radiates the energy in different wave lengths to that in which it was absorbed .
So can you stop light - yes - can you stop radiation in general - no.

Answer 10

To stop light moving put a brick on it. This stops most things. Big things need bigger bricks (or many smaller bricks).

But there is a problem, to put a brick on it you need to catch it. Light moves fast. You therefore need to move faster. But, we are told, nothing moves faster than light.

Therefore the brick solution will only work if you lie in wait for the light and see it coming! But if you see it coming the light has already passed you!