# Einstein and the speed of light

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Lately, I've been getting into Einstein and his theory of relativity, when I, uhh... conceived a thought experiment (can't think of the right words to describe this, so I'm referring to it as a "thought experiment").

Now, as most of us know, Einstein's theory of relativity emphasizes that if something is traveling at the speed of light, time slows down relative to the entity that is traveling.

Logically, this means that if you had a twin, and you hopped on-board a light-speed ship for a couple years while your twin stayed at home, once you made your journey and returned, you would have aged much slower than your twin.

Also, if your twin turned an endless flashlight on, and shined it at your ship as you sped away at light speed, you would never see the light, because your speed would match the light, and you'd constantly be escaping. If you had walkie talkies and your stationary twin tried to send you a message, you'd never receive it, because radio travels at the speed of light.

Now, here's where my "thought experiment" comes in.

Let's assume there's a "Large Human Accelerator," that could safely accelerate a human to the speed of light. The human would remain conscious, healthy, etc. For all intents and purposes, we're assuming that at the speed of light, the human would essentially be moving forward through time more slowly than the stationary accelerator around him, and the control center running the accelerator. Also, for the sake of this situation, lets assume the control center is at the center of the accelerator.

Now, the control center and the human have a walkie talkie with which they are communicating.

Assuming the control sender sends out radio messages, what does the light-speed human hear?

Here's a visual graphic.

The red dot represents the light-speed traveler. The red ring represents the radio signal, also traveling at the speed of light. The blue box is the origin of the signal, the yellow ring is the accelerator and path of the human traveling at light speed.

Now, the theory is that because the human is traveling at light speed, time should slow for him, and as such, when he exits the accelerator after a a year or two, he'll be just a few years older, whereas those in the radio room may very well be dead of old age.

But, if radio communication travels at the speed of light, and he is an equal distance from the source of the communication for the entirety of his time in the accelerator, what would he hear?

And thus is my thought experiment. What are your opinions? Does anyone need clarification? Am I completely misinterpreting the theory of relativity?

Edited by Rabbit

Since he is perceiving time slower than the stationary radio transmitter, he would "hear" the signal slowed down. If it is slowed enough, his receiver would not even be able to convert the signal into audio.

Effectively, the radio signal as perceived by the accelerated man is a lower wavelength than that perceived by the stationary controllers.

Well, that was my first line of thinking, though there's a few issues I can't wrap my mind around.

For what it's worth, I feel that the opposite would happen with the signal. Because everything around him would age more quickly, the signal would actually speed up, as he's traveling forward through time.

But my issue either way is that despite the fact he is moving faster and faster, because he is constantly at the same distance from the radio signal, the signal should constantly hit him at the same rate, regardless of his speed or position. The thought here is that the radio signal is broadcast in all directions, and he is constantly at the exact same distance from the signal, no matter where he is, and no matter what speed he travels. The radio signal also travels at the speed of light, the only thing that doesn't is the movement of the voice of the people transmitting the signal.

Now, I know it's impossible to keep things in this circular motion to begin with and reach the speed of light, it's an entirely new question whether breaking that rule breaks any rules regarding relativity, but I guess that's besides the point...

The duration of the radio signal is something to consider. How many times does, say, a short message repeat in relation to his speed and how many times does it hit him. The other side of this problem is (besides the audio output speed with the accelerated human) does the message make sense if it's constantly arriving at vast speeds in a linguistic/grammar way or is it jumbled to infinity.

Assume the radio signal is constant and is constantly broadcasting in all directions with no interruptions. The traveler is always at an equal distance from the source of the signal. It's really just any standard radio signal.

That's what makes this so interesting to me.

From the point of view of either the traveler or the stationary observer, one is moving extremely fast and one is extremely slow. If they were just shouting at each other, one would sound like he is speaking so slowly you can't even pick up his speaking, one would be speaking so quickly, you'd miss everything. The speed of sound is much slower than the speed of light, thus, it is subject to this manipulation.

However, part of the theory of relativity is that the speed of light does not change relative to the speed of light. What I believe this means is, no matter how fast the traveler is moving, the radio signal will still take the exact same amount of time to get to him. Radio is on the same spectrum as light, it is merely a different frequency.

I suppose it's possible that the traveler would only receive fragments of the signal, as he may very well intersect the radio broadcast so quickly that he only receives pieces of the wavelengths, but that shouldn't' speed or slow the message itself.

Edited by Rabbit

Yeah, I said that backwards, the accelerated man would hear the signal faster, not slower.

the signal should constantly hit him at the same rate, regardless of his speed or position. The thought here is that the radio signal is broadcast in all directions, and he is constantly at the exact same distance from the signal, no matter where he is, and no matter what speed he travels.

Since, from his view, everything outside is moving in slow motion, that doesn't matter.

The radio signal also travels at the speed of light

Only to the operators. The accelerated man would "see" it moving slower than the speed of light. Things can move slower than the speed of light, including light, they are not constant, only the maximum possible speed is constant.

Edit, because you posted while I was writing:

However, part of the theory of relativity is that the speed of light does not change relative to the speed of light.

You understand it wrong.

What that means is that if the man is moving at 99.9% the speed of light and fires a laser before him, he would see it depart at the speed of light - logically 199.9% the speed of light, which is impossible. However, from the man's perspective, he is not moving at all, everything else is moving, therefore the laser is moving at 100% the speed of light. To a stationary observer, the laser is moving at the speed of light, and the man is moving at 99.9% the speed of light, so the laser is only moving .1% the speed of light faster than the man. Of course, since time is relative, both observers are seeing the laser move at the correct speed even though if they were to compare notes, it wouldn't make sense.

I suppose it's possible that the traveler would only receive fragments of the signal, as he may very well intersect the radio broadcast so quickly that he only receives pieces of the wavelengths, but that shouldn't' speed or slow the message itself.

No, you don't skip time. Maybe your tech is insufficient to pick up enough intervals, but that's a different matter.

Btw time dilation is already noticeable on commercial airplanes. https://en.wikipedia.org/wiki/Hafele–Keating_experiment

Edited by Lauren

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