Einstein’s Theory of Relativity states that light (as it is travelling obviously at the speed of light) is so fast that it experiences no (zero) time. Obviously light does move a distance, as thats how we see things as the light bounces off of objects into our eyes, but surely with the equation ‘distance = speed\*time’ and time being zero it implies light doesn’t travel any distance?
In: Physics
Time isn’t zero. Time experienced by somebody sitting on a photon would be zero (or near zero – in the actual universe light often doesn’t travel at the speed of light). But photons travels within the frame of reference of the observer where d=st operates as usual. Photons travel in time – they just don’t ‘know’ that they’re doing it.
Imagine a car going forwards at it’s maximum speed of 100mph. It’s sideways speed is 0mph. if we turn the car 90 degrees now it goes sideways at 100mph, but 0mph in the forward/backwards dimension.
It can travel diagonally, by moving 50mph in the forward/backward dimension, and 50mph in the left/right dimension, for a total speed of 100mph, the maximum.
If you think of Spacetime as 4 dimensions, 3 space and 1 time, light travels at the maximum speed C in 3 of the dimensions, space. This takes all of its “time speed”, making it’s time speed 0 and therefore experiences no time.
We see light move at C, which obviously takes time. This is because our perception of the light traveling can only go at the original maximum speed, so we see it moving. The light photon instantly travels to the destination, but it takes time for its effect to propagate outwards to observers.
Edit: diagonal speeds will not be 50mph. Vector maths means the speeds will be greater, which obviously also applies to spacial and time based motions
> Einstein’s Theory of Relativity states that light (as it is travelling obviously at the speed of light) is so fast that it experiences no (zero) time.
Einstein’s Theory of Relativity actually states that as velocity approaches c, time tends to zero, but that anything traveling *at* c doesn’t have a valid rest frame that can be described within the context of relativity.
This tends to get glossed over in pop sci descriptions but is an important distinction.
That’s the reason why we say that no object can move faster than the speed of light: the object that travels with the speed of light experiences no time, so the speed it *experiences* is (speed = distance/time) is undefined. The closer you approach to the speed of light, the closer the speed you experiences to the infinity and at the speed of light you just have to divide distance by zero to get speed.
At the same time, in our frame of reference (because we move at almost zero speed comparing to light) it’s finite speed and non-zero time.
> so fast that it experiences no (zero) time.
That’s not correct. It does not experience zero time. Time does not apply to light. If you put c speed into the time dilation formula you get division by zero not zero. In the theory of relativity you cannot construct a reference frame that moves along light because that would make speed of light to be zero in that frame and that is prohibited.
Light **alone** cannot be used to measure time and distance without other tools that don’t move at the speed of light.
Distance is velocity * “time in world coordinate system”, which passes at regular rate.
The time the light experiences is irrelevant for that. From the light’s perspective, no time passes so the distance traveled is 0, and because length contraction the distance it perceices really is 0.
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