Is the Location of Light relative due to its speed being constant

In summary, light has a constant speed in all inertial frames, making its location relative to the observer. This is similar to the concept of throwing a ball out of a moving car, where the ball's speed appears different to observers outside and inside the car. However, the path of the light signal through space-time is invariant, meaning all observers agree on which points it passes through and the distance it travels in a given amount of elapsed time. The difference in perception of time passing for different observers accounts for the relative location of the photon at any given point in time after it is emitted.
  • #1
Sicktoaster
6
0
Sorry if this turns out to be a colossally stupid question. I'm a newbie.

But since light has a constant speed in all inertial frames wouldn't that mean where it would end up would have to be relative?

A famous example of relativity for things in inertial frames of reference other than light is throwing a ball out of a car. To someone on the side of the road the ball will appear to go faster than it would from the perspective of a person in the car.

Yet as the ball travels the ball lands will always be exactly the same location for any given amount of elapsed time since it is emitted.

Replace the ball with a photon and now it travels at the same speed regardless of the observer. Does this mean that the location that the photon at any given point of elapsed time after it is emitted is relative?

If not, if the photon post-emission is still in the same exact place relative to either observer what accounts for this?
 
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  • #2
Sicktoaster said:
Replace the ball with a photon and now it travels at the same speed regardless of the observer. Does this mean that the location that the photon at any given point of elapsed time after it is emitted is relative?
Yes. Time and distance are relative (frame-dependent) in just the right ways so that everyone measures the same speed for that photon.
 
  • #3
Just as with the ball, the path of the light signal through space-time is invariant; all observers agree about which points in space-time the light signal passes through, and they all agree that after an interval of time ##\Delta{t}## has passed since the emission of the light, the light will have traveled a distance ##c\Delta{t}## (this is just distance equals speed times time).

Where you're getting in trouble is when you say "for any given amount of elapsed time"; because the observers moving relative to one another see time passing at different rates, they all have a different notion of elapsed time. Thus, there is no such thing as a "given amount of elapsed time" unless you specify which observer's time you're using - and even then the amount of elapsed time is specific to that observer.
 

1. What is the theory of relativity and how does it relate to the speed of light?

The theory of relativity, proposed by Albert Einstein, states that the laws of physics are the same for all observers in uniform motion. This means that the speed of light, which is constant in a vacuum, is also the same for all observers regardless of their relative velocities.

2. How does the constant speed of light affect the location of light?

The constant speed of light means that the location of light is relative to the observer's frame of reference. This means that the location of light will appear to be different for different observers, depending on their relative velocities.

3. Can the location of light be measured accurately due to its constant speed?

Yes, the location of light can be measured accurately, even though its speed is constant. This is because the laws of physics, including the principles of relativity, allow for accurate measurements of the location of light regardless of its speed.

4. How does the constant speed of light impact our understanding of space and time?

The constant speed of light plays a crucial role in our understanding of space and time. It is the basis for the concept of spacetime, where space and time are interconnected and affected by the speed of light. It also affects our understanding of the universe, including the phenomenon of time dilation at high speeds.

5. Is the location of light affected by gravity if its speed is always constant?

Yes, the location of light is affected by gravity, even though its speed is constant. This is because gravity can bend the path of light, causing it to appear to be in a different location for different observers. This phenomenon is known as gravitational lensing and is a key aspect of Einstein's theory of general relativity.

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