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Can light travel "faster than light"?

I don't know much about physics, but I am genuinely interested, and I am only just competent in understanding big physics words. But say if a beam of light is travelling is a straight line through a vacuum at the speed of light. If it approached a planet straight on, surely the gravity of the planet would cause the beam of light to speed up? Increasing it's speed to faster than light?

I don't know if this would apply because light isn't physical, or it is just a wave etc. Anyone like to explain why this is probably wrong?

Reply 1

Beneb

10

I don't know why, but that's definitely wrong.

Reply 2

sadasfa

http://scienceblog.com/light.html :dontknow:

Reply 3

sarsi

9

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961102.html

Reply 4

fron91

Ok here's a try: This a typical comprehension problem when it comes to relatuvity. Nothing can travel faster than light, as to travel at the speed of light in the first place you must have a stationnary mass of 0. I/e you are a photon. For a photon to move faster than c (the speed of light) it would have to have a negative mass. This is impossible to my knowledge. The gravitational pull would have no effect on the light as light weighs 0. That answer your question? :smile:

Reply 5

rezzeJ

No, the speed of light (186,282 mph) is considered to be the 'universal speed limit'.

Reply 6

mattydover

fundamentally for all observers the speed of light is the same as shown by the michelson-morley experiment einstein developed his theories of relativty with this has his basis (amongst many other things people like me have very little comprehension of) i heard that general relativity showed that light could be bent by gravity but sped up ...... i dont know but from all points off reference light travels at the same speed w

Reply 7

hypocriticaljap

2

No, in the same way that a torch beam in a car doing 100mph isn't going at C + 100 mph.

Reply 8

mattydover

fron91

Ok here's a try: This a typical comprehension problem when it comes to relatuvity. Nothing can travel faster than light, as to travel at the speed of light in the first place you must have a stationnary mass of 0. I/e you are a photon. For a photon to move faster than c (the speed of light) it would have to have a negative mass. This is impossible to my knowledge. The gravitational pull would have no effect on the light as light weighs 0. That answer your question? :smile:

but gravity does effect light ... im sure it was proven by eddington and predicted years before by einstein in general relativity

Reply 9

Gavzzz

12

Even though if you accept the Big Bang as fact we can already see that the universe has not had enough time to spread out to the size it is now without matter flying around at FTL. Weird huh? :smile:

Reply 10

TPS.

2

It would bend the light. If the gravity was powerful enough, einstein believed space travel could involve gravity but he himself said it would cost toooo much, and would be very very hard to even find.
You can travel faster than light, I garuntee it. Oh, and theres a word for an object or wave that can travel faster than light in a vacuum. I can't remember it:/

Reply 11

omegaSQU4RED

18

Interesting discussion and one that tests wave-particle duality of light. According to the wave model, light wouldn't be affected by gravitational attraction at all and its speed would not increase. However, according to the particle model, photons have mass, meaning that they would undergo a gravitational acceleration (albeit very small).

Reply 12

Torresisagod

Yeeah I think you're kind of right? Gravity can fractionally speed up light

Reply 13

fron91

mattydover

but gravity does effect light ... im sure it was proven by eddington and predicted years before by einstein in general relativity

As in it bends it? hmm if that is possible that goes way over my physics knowledge haha. I only know that light cannot be accelerated as it would have to weigh less than nothing :confused:

Reply 14

paddyman4

14

Gavzzz

Even though if you accept the Big Bang as fact we can already see that the universe has not had enough time to spread out to the size it is now without matter flying around at FTL. Weird huh? :smile:

Weird. Also complete bull.

To the OP, I think this is a case where it's better to think of light as a wave. Your logic would also ask whether light trying to escape a black hole would slow down to zero, another impossibility. In that case rather than thinking of a photon failing to escape, you should think of a wave that is infinitely redshifted. This is the effect of gravity on light - altering the wavelength. In your example the effect of gravity would be to blueshift the incoming light. A classical imagining of what's going on is never going to work because classical physics doesn't apply in these situations. You'd have to turn to general relativity. When people talk about gravity bending light it makes it sound like gravity affects light like it would a tennis ball. In fact in that case light is still going in a straight line, but gravity has altered the curvature of space such that a straight line to the photon looks like a curved path to the external observer.

Reply 15

dbmag9

15

Light travels at a constant speed for all observers, and passes through the shortest path in 4D space-time. When light passes a massive object (like ur mum lolz) and seems to bend, it is in fact travelling in a straight line through curved space.

I'd guess that in the case where it's travelling directly into such an object, observers would still see the event as though the light were travelling regular speed, but it would in seem to be a shorter distance because space is 'squashed' around the object. Something like that, anyway.

Edited to make less nonsense. My only qualification in this is the IB Physics HL option topic on relativity.

Reply 16

spex

16

How many people here actually know what they're talking about?

Reply 17

dknt

12

No light wouldn't speed up. Usually, something would speed up. However as light is the universal speed limit, rather than that extra energy it gets, due to gravity, increasing its speed, the light just becomes a higher frequency i.e. more blue. And vice-a-versa, light going away fro ma gravity souce would not slow down, but rather lose energy, in the form of its photon energy i.e. more red.

Reply 18

Gavzzz

12

paddyman4

Weird. Also complete bull.

How so? you not a believer in the BB?

Reply 19

fishpie57

My first guess would be that although the light would accelerate, this doesn't mean 'speeding up' but just changing direction. It would be like circular motion, where the light would accelerate towards the planet, but would still cover the same distance in the same amount of time. So it would still travel at the speed of light, but its velocity (speed with direction) would change.

Interesting question, though! The speed of light has to be the speed limit of the universe, because of Einstein and E=mc^2 and stuff getting heavier as it gets faster...

Meh. I'm sure someone else can explain all this far better than me. I love the topic of relativity :biggrin: