How does physics explain the discrepency between relativitey and the speed of light?

Question

Speed of light: The maximum speed an object can have, and its impossible to go faster.
Relativity: For example, a train is moving at 60 mph, you are on the train and throw a rock from the front in the direction of travel at 10 mph. Relative to the ground, the rock is traveling at 70 mph.

Problem: We assume there is a zero velocity point in the universe, say the exact middle or the place of the big bang or whatever, and that the universe is always expanding, therefore has a positive velocity in some direction outward. If the Earth is moving away from the center of the universe at 0.5 times the speed of light and we launch a satellite in the same direction at 0.75 times the speed of light, it should be going at 1.25 times the speed of light from the perspective of the zero velocity point. How is this possible if the speed of light is the maximum that any object can travel?

Answer 1

Your problem is in assuming that at high speeds, the velocity of B is equal to the velocity of A plus the velocity of B relative to A. The expression v(A) = v(B) + v(A|B) is an approximation of a more complicated relationship that takes into account the impossibility of going faster than the speed of light. That is what the theory of relativity is all about, and since I can't say more without saying much. much more, I'll leave it at that.

Answer 2

Simple arithmetic tells you that the sattelite SHOULD be traveling at 1.25 times light speed, but the physics of the universe says it cannot, and, the math used to work quantum phyisics proves it very consistantly.

It's just a fact that there are limiting factors. Not exactly the same thing, but I can use the train and rock analogy to make a point. If the train was traveling at such a velocity that the wind resistance passing by the train was such that you couln't throw the rock hard enough to overcome that resistance, then the rock wouldn't go any faster than the train.

This is an oversimplification, but, I hope you see my point. Simple arithmetic is unable to factor in EVERYTHING involved in accellerating matter to light speed.

I LIKE "brewer-engineer"s scissors analogy. I like another. Say you could set up a wire, or rope, perfectly straight, from our star to the next nearest. You could arrange a system where tugs on the rope would be equivialant to Morse code. A tug at one end would be instantly felt on the other. In this analogy, information could be sent "faster than light could travel" the same distance (about 4 years).

Answer 3

You have misconceptions about both Relativity and the Big Bang.

The Big Bang did not start at some point in the universe, sending stuff out in all directions. It says is that space was smaller and hotter in the past everywhere. The universe is evenly filled with galaxies everywhere, but the distances between them were smaller in the past. There is no center to the expansion--- the expansion is the same everywhere.

According to Relativity, speeds don't add up the way you think they do. When you throw a baseball at 10 mph in a train going 60 mph, the resulting motion is *not* 70 mph. It's very slightly smaller. For motions that are near the speed of light, remove the "slightly smaller" qualification. If the baseball were thrown at .9c in a train going .9c, the resulting motion is .99c, not 1.8c.

Answer 4

(see
http://answers.yahoo.com/question/index;_ylt=AqQPNbfwjWG1ETO5m4wzic7ty6IX?qid=20070809175558AA9vMl7&show=7#profile-info-zeCZiR6Taa
for a similar question)

First you can't go the speed fo light, you would get a divide by zero error. (Your mass gets too close to infinite, time slows too close to stopped, and your hair gets all mussed)
The only limitation to going faster than the speed of light is the need to cross the speed-of-light barrier to get there.

Approaching the speed of light, there are two main characteristics that are not apparent at human's normal SLOW speeds.

First, is that while F=ma would seem to indicate that an object moving at near the speed of light could close the gap easily, the object's mass increases with the speed, approaching infinite mass as it approaches the speed of light. So whats needed to get even a slight acceleration also approaches infinite force.

Second, is that the object's time frame slows. This affects the measurement of speed in different frames. To quote from the other question's answer:

If you got up to 99.99% the speed of light and turned on your headlights, the light from your headlights would be moving at the same speed as the light from the lamppost you are passing, but would be blue-shifted far out of the visible range (to xrays?) to the pedestrian in front of you.
Note that you would measure the light as moving away from you at the speed of light, and the pedestrian you passed would also measure the light as moving away from him/her/it at the speed of light. It works because your clocks are running at different rates.

So all of the light is moving at the same speed!

Finally, according to relativity, there is no absolute reference. So there is no single zero velocity point. EVERY point is the zero velocity point of its own reference frame. When we look at the stars, they are all red shifted (a FEW exceptions) because the earth is the center of the universe after all! (for us)

Answer 5

The problem with your analysis is that the speed of 0.5 is a constant through out the Universe and in effect is moot. WIth in the frame of refrence of the Universe in its entirety everything is moving at 0.5 therefore 0.5 can become the defacto value for 0 where all things are at rest.
The real problem with your analogy is that the Train car in which you are throwing the baseball is in fact representative of the Universe. Since we currently define the Universe where all things exist there is no way for anyone to be outside the Universe to act as an outside refrence.

Answer 6

First off, you're assuming we're already moving at relativistic velocities. We don't know this.
Try another experiment. Let's assume we could make an imaginary point move faster than light. Suppose you have a 93,000,000 mile long pair of scissors that are opened. You close them fast. The point of intersection then moves faster than light.
Ha.........try to get two rigid beams (scissors) to stay rigid over that distance. Thought experiments can be fun.

Answer 7

Velocity is calculated as follows.
V^2 = Pressure of space/density of the moving mass
The presure on the mass =Mc^2/volume of the mass
Density is mass per unit volume.

So the pressure to contain a particle of light is the greaterst in the Universe and it varies at different parts of the Universe which have different densities.
So no matter where a gross mass structure is in the universe it would never be able to move at the velocity of light.

Answer 8

You can't use simple velocity addition at close to light speeds. You have to use a scaling factor called gamma.

Answer 9

There is no fixed point to measure from in relativity. In
Newtonian physics there is, that is one of the most important
differences in the two theories.