View Full Version : Relativity and Electronics

2004-Nov-29, 02:55 AM
Help me out on this one, electronics and computer science aren't my strong point.

At higher velocities, would the barrier of 'c' prevent the proper use of computers and electronics in a ship?

I think about a "comm" signal travelling from the back to the front, it will take a lot longer for the message to go forward than back, since the barrier of 'c' prevents the electrons from 'seeming' to move at c (since the ship is going so fast).

Sorry the question is vague. I guess my question is whether electronics would be affected a high relative velocities.

2004-Nov-29, 05:38 AM
Actual electrons in a circuit move very slowly (and in an AC current have no net movement), but the electric field travels at c. If electricity travelled at the speed of the electrons there would be a noticable time difference between flicking the switch and a light turning on, but there isn't.

2004-Nov-29, 03:03 PM
Imagine a ship 10 miles long and travelling at 99.9% c as compared to earth.
If that were the case, and it took a mere billionth of a second to send a signal from the front to the back, it would still take a billionth of a second to make the return journey to the front.

Since we simply consider the view of an observer on the ship, the formulas for time and speed are easy. Distance = speed * time.

No fancy theories to worry about.

2004-Nov-29, 03:42 PM
Originally posted by alainprice@Nov 29 2004, 03:03 PM
Imagine a ship 10 miles long ... and it took a mere billionth of a second to send a signal from the front to the back.
Matthew and alainprice make most of the case for you. Here's a minor quibble, that doesn't change the important part of what they've told you.

Light travels about one foot per nanosecond [billionth of a second], If you were using optical signals [not the slower electronic variety], it would take about 53 microseconds for signals to go from one end of the ship to the other [in the frame of the ship].

2004-Nov-29, 10:56 PM
Even at 99% of c, the signal would still travel - relative to the ship - at the speed of light?

Wouldn't blue, and red-shifting be a big issue, as well?

2004-Nov-29, 11:38 PM

All the effects you are describing only apply to someone apart from the vessel. The person that's measuring the ship's speed as 0.99 c is the same person that experiences the red/blue shifted signal.

That's the beauty of relativity. It's not what's happening that's important, but rather what you measure. And what you measure depends on your speed. Since a person ON the ship thinks he has a speed of 0(and rightfully so), he experiences no relativistic effects.


I meant NO to the color shifting questions.

as for: "Even at 99% of c, the signal would still travel - relative to the ship - at the speed of light?"
Exactly. The reason for that is quite simple. No matter what experiment you do, you will always measure the speed of light(in a vacuum) to be the same. No matter what.

2004-Nov-30, 06:18 AM
All the relativistic effseem to happen to whats outside the ship, not whats inside.

2004-Nov-30, 01:06 PM
Even better, both.

Imagine now the ship and the observer are flying(coasting really) apart, so that their light is red-shifted. The person on the ship would feel as if he's at rest, and notice nothing wrong. Same with the observer, he would feel at rest, and only notice that something is wrong when he looks at the ship. These two observers would see each other as being red shifted. Their images are both red-shifted and normal at the same time. They would not agree on who was actually red-shifted. The answer is easy, it's both.