- #1
runeks
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I'd like to share some thoughts I have had on faster than light travel, and hear from you if it really can be that simple. In short, it can be said that if we believe to have proven the relativity of the speed of light, faster than light travel is, by definition, impossible. No formulas, no big thought experiments about me sending messages back in time, just a simple assertion that if we assume relativity of the speed of light to the observer - which, as I spontaneously realize later on in this post, is simply proven - faster than light travel is impossible, by definition.
I mean, how could it be otherwise. If we always measure the speed of light to be c, then how can we ever move faster than it?
And what does moving faster than it mean? It seems obvious to me that movement has to be relative to some reference. In this sense, what does faster than mean? As far as I can tell, for example when overtaking someone on the highway, object A moving faster than object B means that object A is moving away from object C at a faster speed than object B is moving away from object C. Ie. faster than always has to include a third object, because if we only have object A and object B (and A is overtaking B), A is just moving away from object B, nothing else is happening. No one is moving faster in any sense.
This leads us to the seeming fact that the word faster than only makes sense when three object are involved. In the case of light, only two "objects" are involved - something moving and light, and the concept faster than no longer makes any sense.
Of course, if we define "faster than light travel" as based on the speed of movement of an object relative to the light I see, then it's possible. It happens when I turn on a lamp that faces one direction, and some other person walks in the opposite direction at, for example, 5 km/h. He will then be moving, according to my experience, at c+5 km/h.
But I guess my main point is, why are we even discussing "faster than light travel" when relativity seems to have proven that it is impossible? Unless I am misunderstanding something, and the relativity of the speed of light hasn't been proven. Though as far as I know, we've measured clocks on space ships moving relative to us, and confirmed that their clocks have "lost" time, hence the theory must be true. Actually, thinking of it, we can "prove" the relativity of the speed of light just by someone measuring the speed of light of a laser beam, while moving in a car, and me standing and the side of the road measuring the same laser beam.
If we get the same results, the speed of light is relative to the observer and faster than light travel is by definition impossible. Unless we define the travel as relative to me, and the light I see. Then it happens as soon as something moves.
I mean, how could it be otherwise. If we always measure the speed of light to be c, then how can we ever move faster than it?
And what does moving faster than it mean? It seems obvious to me that movement has to be relative to some reference. In this sense, what does faster than mean? As far as I can tell, for example when overtaking someone on the highway, object A moving faster than object B means that object A is moving away from object C at a faster speed than object B is moving away from object C. Ie. faster than always has to include a third object, because if we only have object A and object B (and A is overtaking B), A is just moving away from object B, nothing else is happening. No one is moving faster in any sense.
This leads us to the seeming fact that the word faster than only makes sense when three object are involved. In the case of light, only two "objects" are involved - something moving and light, and the concept faster than no longer makes any sense.
Of course, if we define "faster than light travel" as based on the speed of movement of an object relative to the light I see, then it's possible. It happens when I turn on a lamp that faces one direction, and some other person walks in the opposite direction at, for example, 5 km/h. He will then be moving, according to my experience, at c+5 km/h.
But I guess my main point is, why are we even discussing "faster than light travel" when relativity seems to have proven that it is impossible? Unless I am misunderstanding something, and the relativity of the speed of light hasn't been proven. Though as far as I know, we've measured clocks on space ships moving relative to us, and confirmed that their clocks have "lost" time, hence the theory must be true. Actually, thinking of it, we can "prove" the relativity of the speed of light just by someone measuring the speed of light of a laser beam, while moving in a car, and me standing and the side of the road measuring the same laser beam.
If we get the same results, the speed of light is relative to the observer and faster than light travel is by definition impossible. Unless we define the travel as relative to me, and the light I see. Then it happens as soon as something moves.