How Fast Do Forces Like Gravity and Magnetism Act Compared to Light?

[MadScientist 1000]

Just to go for the record to prevent any threads like this from popping up:

1. Nothing outruns light.
2. All forces operate at the speed of light in a perfect vacuum.
3. Please do not post dumb questions like this ever without considerable research on the subject.

 

[HallsofIvy]

Also - in the recent Nova special about Einstein they showed his "thought" experiment of looking into a mirror while traveling at the speed of light. He theorized that you would never see your reflection because the light couldn't travel faster than you in order for your eyes to see the reflection.

I doubt you saw that. In fact, I suspect you misinterpreted an argument of just the opposite. All motion is relative- it makes no sense to talk about moving near the speed of light (of course, you can't move "at the speed of light") without saying what that speed is relative to. If you and the mirror are moving, relative to the earth, at the same very high speed, then you and the mirror are motionless relative to each other. The situation would be exactly the same as if you were sitting at home.

But here's my QUESTION:
If you and a friend are holding a mirror BEFORE going the speed of light, and you both see your reflection...what happens to that reflection once you REACH the speed of light and the friend moves out of the way of the mirror? Will her reflection still be there and stay there until you decelerate?

Thanks in advance for your responses! I live in a rural area...and I can't find anyone willing to ponder this stuff with me!

You CAN'T "reach the speed of light". Even allowing for that, your question is ambiguous. Do both you and your friend accelerate or just you? Why does your friend "move out of the way of the mirror"? Was he blocking your view to begin with?

 

[m_haseli]

In fact light is the fastest.
I want to tell you an example of faster velocity than light.
Intefering two or more monochromatic waves we find two different velocities,
Phase velocity & group velocity.
Phase velocity can be more than the speed of light,but not the group velocity.
In fact it 's the group velocity that carries the energy,and phase velocity doesn't do.
So, all the physical information carrying pulses transport slower than light or as fast as that.

 

[disregardthat]

What is the phase velocity, if it is not photons, why does it excist?

 

[Claude Bile]

Phase velocity is the speed at which the nodes (or another point of constant phase) propagates in a wave packet.

Group velocity is the speed at which the wave packet itself propagates.

A wave packet is simply a collection of one or more frequencies propagating together.

Claude.

 

[twofish-quant]

The content of the paper seems plausible. It is worth reading http://www.metaresearch.org/cosmology/speed_of_gravity.asp

This is pretty wrong. If you have a situation in which the force points at where the sun was a few minutes ago, then yes you will get a system that is unstable, but gravity doesn't work that way. Gravity works with fields, not forces.

Imagine a ball rolling on a rubber sheet. The ball causes a depression on the rubber sheet that spreads outward at the speed of light. Now imagine the ball starting to move. The depression will start to bunch up in front of the ball, and expand behind the ball. Now you ask in what direction the forces will point at, and it turns out that they will point directly at where the ball is at a particular moment rather than were the ball was a few minutes ago.

 

[twofish-quant]

The reason you can't exceed the speed of light is that the speed of light is always the same. One really *weird* thing about light is that it always seems to be traveling at the same speed. If you run after a car, then if you run fast enough, then you will catch up with it. If a car is running at 50 mph, you run toward it at 10 mph, the car will appear to be moving away at 40 mph. If you run in the opposite direction the car will be moving way at 60 mph.

Light doesn't work this way. No matter how fast you are running, a beam of light is always moving away from you at the same speed. If you run toward a beam of light at 10 mph, the speed of light will be c. If you run away from a beam of light at 10 mph, 100 mph, 10000 mph, the speed of light will still be c.

This is weird, but it seems to he how the universe works.

 

[Sorry!]

This thread was also started 4 years ago.