three speeds at once.

[losfomot]

First off, I am not an expert... take what I say with a grain of salt... and maybe some lemon.

 

Special relativity states that the speed of light is constant for all observers, whether they're traveling at 1 m/s or 99.9% the speed of light, light travels at c, which is approximately 300,000,000 m/s. However, in my tiny little mind, this statement makes about as much sense as "afdjaojvalfjdl;kj!"

 

Suppose for a minute that a spaceship is flying at 150,000,000 m/s relative to a planet. To the planet, the light reflecting off the ship is traveling at 300,000,000 m/s, but to the spaceship, it's traveling at 450,000,000 m/s relative to the planet.

 

So in conclusion that means that the same light, the light being observed by both parties at the same time, is traveling at two speeds at once. That doesn't make a bit of sense. How can an object have more than one speed at one time?

 

I'm sure this has been brought up before in the over a century that this theory has yet to be disproven, but I seem to have been home sick that day. What's the answer?

 

 

 

Suppose for a minute that a spaceship is flying at 150,000 Km/s past Earth.

 

An Earth observer watches the ship go by and measures the ships velocity as 1/2 the speed of light. Suddenly the ship emits a flash of red light. 10 seconds later a beam of light bursts forth from the front of the spaceship. Earth observer sees the lightbeam moving forward at (obviously) the speed of light. The Earth observer says:

 

'The beam of light is moving at 1/2 the speed of light relative to the spaceship'

 

This is an example of erroneously mixing frames. A cannot decide how B is moving relative to C (at least not by observation and measurement alone)

The reason for this is that the two observers (A and B) see the universe differently. Lets go back to our event, but this time from the Spaceships point of view...

 

A spaceship is traveling past the Earth at 1/2 the speed of light. As he goes past, he decides to turn on his headlights. He flicks a switch and a red flash of light is given off... 8.5 seconds later a bright beam of light (the headlight) shoots out in front of the ship moving away from the ship at (obviously) the speed of light. The observer on the spaceship thinks about it and decides:

 

'I'm moving at 150,000 Km/s relative to Earth, and my headlight is moving away from me at an additional 300,000 Km/s, so the beam of light must be moving at about 450,000 Km/s relative to the Earth'

 

Again, incorrectly mixing frames.

 

But You will notice that the time between the flash and the headlight turning on was 10 seconds for the Earth observer, but only 8.5 seconds for the Spaceship occupant. This is because of time dilation. Time dilation is a contributing factor as to why you cannot mix frames... different amounts of time have passed for the two observers over the course of the same event.

 

Lets pick another event to analyze...

 

The Earth observer watches as the spaceship headlights are turned on. Ten seconds later, the beam of light has traveled a total of 3,000,000 Km, and the space ship has traveled 1,500,000 Km in the same direction, so the Earth observer sees that, in 10 seconds, the beam of light has traveled only 1,500,000 Km relative to the Spaceship.

 

Now we know that the beam of light is actually moving at the speed of light relative to the spaceship, so in those 10 seconds the light beam should have traveled 3,000,000 Km ahead of the Spaceship, but Earth sees the light beam only 1,500,000 Km ahead... what explains this discrepancy?

 

First of all, remember that, although 10 seconds have gone by on Earth, only 8.5 seconds have gone by for the spaceship, so 8.5 seconds X the speed of light = about 2,550,000 Km. That gets us part of the way to the 1,500,000 Km that Earth sees, but its not nearly enough... so we guess that time dilation cannot be solely responsible for the difference... and we're right.

 

Another consequence of relativistic speed is length contraction. The faster you go in a given direction, the shorter the distance gets in that direction.

 

What this means for our spaceship guy is... hmmm

 

Lets say that, as the ship passes by Earth, it is heading directly toward the Sun. From Earth's point of view, the spaceship is 150,000,000 Km from the Sun. From the Spaceship's POV, the Spaceship is only about 130,000,000 Km from the Sun. This is not an illusion, the spaceship exists in a universe where the distance really is 20,000,000 Km less than it is in the Earth observer's universe.

 

It is a combination of time dilation and length contraction that explains the apparent contradiction between what each observer sees. For the Earth observer, X amount of time has gone by, and Y amount of distance has been covered for the spaceship to get from Point A to Point B. For the Spaceship observer, not only has less time gone by during the same event, but Point A and Point B are closer together, so less distance was traveled.

 

The speed of light is constant in any frame. Einstein realized this and tried to think of a set of rules the universe must have that would allow this to be true. Time dilation, length contraction, and other things collectively known as Special Relativity was the explanation he came up with. It works very well in allowing the speed of light to be constant in all frames, and has other consequences, many of which have been experimentally verified.

 

I hope I haven't mucked things up too much.

 

faster than it was before. relative to its previous speed.

 

relative to it's previous speed relative to what?

 

but still even at that i think you could calculate the middle of the universe from an energy point of view, the center of mass of the universe and you would do that by finding the "middlepoint" from which everything seems to be moving from, taking into account they speed direction and mass.

 

But that's just it, there is no direction that everything is moving away from more prominently than any other direction. We have looked at the universe, and 'taking into account they speed direction and mass', we find everything is moving away from everything else equally. (not counting the Great Attractor which I believe, relative to the size of the universe, is a local phenomenon.)

[Norman Albers]

There is no absolute location, coordinate sets are arbitrary you can set them up however you like :'(

 

There have been several experiments to show there is no absolute rest frame

 

Which you can't do with temperature...

 

Klaynos, this statement on temperature is important. To me it reflects how a blackbody spectrum infers a body, or at least it assumes a radiation distribution in equilibrium with "a wall" of atomic emitters. Do you agree? By itself, the photon field does not constitute a statistical kinetic ensemble......In this thread we have been rock-and-rolling with several questions. I am hoping people knowing more cosmology than I will say more on questions in the large.

[Quartile]

afaik, gravity travels faster than light.

 

pending many studies and the conclusion that they bring to science.

[Klaynos]

afaik, gravity travels faster than light.

 

pending many studies and the conclusion that they bring to science.

 

Most gravity theories that I know of say that gravity travels at the speed of light... What sources can you site that say otherwise?

[swansont]

afaik, gravity travels faster than light.

 

pending many studies and the conclusion that they bring to science.

 

The ones with which I am familiar make the wrong measurements or draw invalid conclusions from the measurements. If one compares gravity with light, one gets the wrong answer as the retardation effects are different. Light comes from e.g. where the sun was 8 minutes ago, but gravity comes from where the sun is now. But that's consistent with GR and gravity travelling at c.

[Quartile]

faster than or at the same speed as, either way

 

regardless, gravity is not electromagnetic

 

i dont write down sources, but there have been several studies that ive read that have fairly arbitrary, theoretically-based values for the speed of gravity at many times c. there has not been evidence enough to prove anything conclusively, and I doubt that a scientific journal or team would want to publish anything another than c for the speed of gravity simply because of the amount of scrutiny it brings.

 

its a hot topic

[Norman Albers]

In my papers I am realizing E&M and gravitation as polar and nonpolar manifestations of the vacuum polarizability.

[swansont]

faster than or at the same speed as, either way

 

regardless, gravity is not electromagnetic

 

i dont write down sources, but there have been several studies that ive read that have fairly arbitrary, theoretically-based values for the speed of gravity at many times c. there has not been evidence enough to prove anything conclusively, and I doubt that a scientific journal or team would want to publish anything another than c for the speed of gravity simply because of the amount of scrutiny it brings.

 

its a hot topic

 

If somebody had legitimate data that demonstrated this, they would publish, precisely because of the scrutiny it would bring. They would have a leg up on a Nobel prize.