I have read somewhere that light always moves relative to a traveller at the speed of light, but also that even if that traveller is moving the light beam will still be moving away from the traveller heading in the same direction at the speed of light. Is this correct and if so how is it possible? I would think that if a traveller is indeed heading in the same direction as a beam of light, at, say, half the speed of light, then the beam of light would be moving away from them only at a speed of half the speed of light. Anything more would mean that the light is travelling faster than the speed of light to a thrid party observer (which isn't possible). Can anyone clarify or did I read this fact wrong.
2006-09-17 15:25:22 · 9 answers · asked by midwestbruin 3 in Science & Mathematics ➔ Physics
Welcome to special relativity.
No, you won't be able to catch the speed of light. Once the light is ahead of you, the fastest you can travel is the speed of light. Therefore, the light(also traveling the speed of light) will always be ahead of you.
The concept that light always travels the same speed was the conclusion of Maxwell's equations. Einstien had the thought that time is not constant for all observers. As you travel faster, your time slows down. In the above example, your time would go by at half the rate as if you were still. So the light will still appear to be moving away from you at the speed of light.
2006-09-17 15:39:12 · answer #1 · answered by something 3 · 0⤊ 0⤋
You read it right, that's **exactly** what happens. The traveller sees the beam of light move away from him at the speed of light, the 3'rd observer sees the beam of light moving at the speed of light and the traveller moving at half the speed of light, and it will take you about 3 years of University level Physics to learn enough Special Relativity to understand why.
Doug
2006-09-17 15:36:06 · answer #2 · answered by doug_donaghue 7 · 0⤊ 0⤋
The answerers that said the beam of light still proceeds away from the traveller "at the speed of light" were all correct.
However, those who said the traveller would "still be moving at 1/2 the speed of light" were not totally on track.
Anytime we start talking about relative speeds here, we need to ask "according to whom?" According to a stationary observer, the traveller who thinks he is buzzing along at 1/2 the speed of light (c) , would only be cruising at 43.3% of c. The time dilation formula from Special Relativity is:
t1 = t0/sqrt(1-(v^2/c^2))
i.e., the time it takes for the traveller to go from point A to B, at a velocity of .5 * c, is inflated by about 15%, according to the stationary observer.
The main point: if you work all the formulas for both the stationary and moving observers, you end up with light still moving at c for everybody.
Notes:
1. Catching up with the beam and watching it recede into the flashlight--not going to happen. The light beam would continue to streak ahead. You would be hobbled by the "speed limit" of c (stationary observers would note that your speed was tailing off just below c, even though you were throwing extra coals on the fire).
2. Axiomatic and never questioned? Whoa--consider: the speed of light has been measured many times. Issues like time dilation are everyday facts of life in particle accelerators, where the byproducts of high-speed collisions "hang around" for much longer than they "should," thanks to many well-established and tested facts coming out of Special Relativity.
2006-09-18 01:10:26 · answer #3 · answered by EXPO 3 · 0⤊ 0⤋
Actually, there is one thing that everyone has failed to note: the "speed of light" generally refers to the speed of light in a vacuum. When light travels through a medium (such as air or glass) it slows down. This is because the photons get absorbed by atoms then re-emitted along the way. Therefore it is possible to shine light on a substance through which light travels quite slowly, then simply travel around the substance and meet it at the other side. See the link below for a description of how scientists slowed the speed of light to just 38miles per hour.
2006-09-17 16:17:39 · answer #4 · answered by Anisha 1 · 0⤊ 0⤋
Most of the answers you've received so far look pretty good - however, I just have to throw in this curve.
Imagine you and a beam of light betting on who can get to a designated point in space first:
Because space is deformed and warped around large objects, if you find a "straighter" path in trying to catch the light, and the light experiences several "detours" and has to travel a greater distance while bending through the gravitational fields, you will indeed pass that beam of light without ever exceeding its velocity because you will be actually covering more relative distance in the same amount of time!
Isn't physics great?
2006-09-17 16:06:37 · answer #5 · answered by LeAnne 7 · 0⤊ 0⤋
light is emitted at the same speed no matter how fast the source was travleing. if you sent out a beam of light, then took off at faster than the speed of light in that same direction you would catch up to the end of the beam. you would theoretically be able to watch the beam of light shrink back into the emitter. and once you passed the end then no more light would be comming out.untill you slowed down enough to let the light come out of the emitter. so no light is not relative.
2006-09-17 15:48:38 · answer #6 · answered by bishop 1 · 0⤊ 0⤋
it is strange but true...in fact it is an axiom of the special theory of relativity. instead of dealing with relevant velocitys and perform vectorial thnking and sloving the speed fo light is the same for all observers. no matter their relative velocity (as in newtonia physics) each obserever can expirience the speed of light the same as all the others. no matter if one is movving awway from a light beem no matter if he is closing too fast the speed of lights remains the same for all. it is quite something to come to realize but once you do it you will understand many things relting to relativity theories. Axioms are defined not proven and whole theories are made based on them. Euclidean geometry is based on the fact that 2 parallel lines never cross each other. some would argue with that back whole building and great technological -mechanical achievements were made due to this. who knows if ther theoties based on other axioms will be adopted then further progress can be made.
what you shoud realize is that your question is answered by an axiom and axiom are never questioned. it is the first step to base theories.
2006-09-17 18:46:12 · answer #7 · answered by Emmanuel P 3 · 0⤊ 0⤋
yes, light will continue to move at the same speed and away from the traveller, but only at the speed of light minus the speed of the traveller.
Seems as though you misunderstood what you read.
2006-09-17 15:34:56 · answer #8 · answered by freetronics 5 · 0⤊ 0⤋
Yes, you are correct... (see special relativity)
physics must be the same in every reference frame.
2006-09-17 16:32:48 · answer #9 · answered by tomz17 2 · 0⤊ 0⤋