The Speed Of Light ??

[MRC01]

There is no difference between traveling away from earth and returning again. In both cases time dilation occurs with the time for the traveler running slower both on the way out and on the way back again. Traveling on the way back doesn't cancel out the time dilation on the way out.

Yes, but if the traveler is near the speed of light relative to the Earth, all we have is 2 things (the Earth & the traveler) moving relative to each other near the speed of light. Each sees the other as moving and motion is relative. How does the universe know to slow down time for one, and speed it up for the other? This is the dilemma or paradox of the traveling twins.

And it is also important to point out that this is always in reference to some outside observer. For the traveler's and the observer's clocks, a second is still a second, and year is still a year to them You're both aging in your own reference frame. It all traces back to the fact that the speed of light is a constant in both frames.

This gets close to the answer. The answer is that one only one of them (the Earth or the traveler) underwent acceleration. This means the two frames of reference are not equal - the traveler's is non-inertial. That is how the universe knows to "slow down" time for him but not for the Earth.

 

[billt460]

Not quite enough difference between the Pole and Singapore to measure.

Remember, you’re comparing to C - which is, roughly 669,000,000 miles an hour. That’s 669 MILLION - so, a thousand or so either way? Not enough.

But 18,000? The difference between an orbiting satellite and a person on the ground?

Yep, measurable difference.

So these people who are on the ISS for almost a year have slightly increased their lives by a measurable amount? (17,500 MPH for close to a year).

 

[Astro14]

I don't know if this guy is right or wrong about this. But how can the speed of light work going away, but not coming back, when both speeds and distances are equal?

He’s right.

The key points -

“From your perspective”
“Back on Earth”

 

[Astro14]

So these people who are on the ISS for almost a year have slightly increased their lives by a measurable amount? (17,500 MPH for close to a year).

Yep. Small, but measurable. They gained a few seconds during that time.

In order for GPS to work, it has to be accurate to around a 10 billionth of a second. With that level of precision, the difference in the speed of the clock on board the satellite is measurably slower.

 

[JeffKeryk]

@billt460 I've seen Professor Cox speak several times. Highly recommended, when he comes to your town. You may be interested in the KIPAC lectures I post from time to time.

If nothing else, it gives one perspective of our place in the Universe.

 

[kschachn]

So these people who are on the ISS for almost a year have slightly increased their lives by a measurable amount? (17,500 MPH for close to a year).

Only as compared to someone who was travelling slower than they were. From their perspective, no. They still had the same lifetime measured by their clock, whatever that may be.

 

[billt460]

So..... If you were in your car, traveling through space at near the speed of light, the stars you look at through your windshield would be twice as bright as you bear down on them.

While the stars in your rear view mirror would barely be visible because you're out running their light.

 

[kschachn]

So..... If you were in your car, traveling through space at near the speed of light, the stars you look at through your windshield would be twice as bright as you bear down on them.

While the stars in your rear view mirror would barely be visible because you're out running their light.

Nope, this is the whole point. The speed of light is a constant and does not vary in relation to the observer's velocity. The absolute value of c can change but not due to this.

Relative speed changes affect frequency and wavelength in light, not velocity.

 

[billt460]

Nope, this is the whole point. The speed of light is a constant and does not vary in relation to the observer's velocity. The absolute value of c can change but not due to this.

It's not like sound waves that bunch up and then spread out.

But if you are traveling away from a source of light at the same speed it is traveling at you, how can it reach you?

By the same token, if you are traveling AT the same light source, it's coming at you at a combined double the speed.

A bit like that whole deal of a 12" ruler only being 6" long as it sped by you at half the speed of light.

 

[kschachn]

But if you are traveling away from a source of light at the same speed it is traveling at you, how can it reach you?

By the same token, if you are traveling AT the same light source, it's coming at you at a combined double the speed.

A bit like that whole deal of a 12" ruler only being 6" long as it sped by you at half the speed of light.

I changed my post a bit, perhaps that is better.

For one thing you will never travel at the same speed as light. That is impossible. No object with mass can ever travel at the speed of light.

The rest of it you'll have to pick up on your own. The constancy of the speed of light is very complex, it's not Newtonian and measured by rulers. Check out the Lorentz equations and Special Relativity.

 

[JimPghPA]

The Special Theory of Relativity explains it. Time slows down ( FOR YOU ) if you're traveling close to the speed of light.

Fixed it for you.

 

[Leo99]

Fixed it for you.

Time slow down for you relative to a "stationary" person. It's all relative, man.

 

[Astro14]

So..... If you were in your car, traveling through space at near the speed of light, the stars you look at through your windshield would be twice as bright as you bear down on them.

While the stars in your rear view mirror would barely be visible because you're out running their light.

No. Not exactly.

First, the brightness has nothing to do, directly, with the velocity of the star.

The velocity of the star, relative to the observer, red-shifts (going away from you) or blue shifts (coming towards you) the light that you, the observer, see from that moving object.

Now, blue light is brighter (more energetic) and at high relativistic speeds, there can be some relativistic “beaming”, or apparent amplification of luminosity by a jet of energetic (light emitting) matter coming at the observer. We see this in astronomy - it’s measurable. There are objects in the universe that emit matter at very high speeds, and it is blue-shifted and more luminous than it would be if it were going slower.

But…in your relativistic car, you’re not “outrunning” their light - because, for you, at near the speed of light, time has slowed. So, what you see is the light coming at you from both sources at, well, the speed of light, though with significant blue and red shift.

There are several difficult, but important, concepts when discussing special relativity.

The first is that there is no absolute velocity, only velocities relative to you, the observer.
The next is that the perceived speed of light is a constant, C.
The next is that you can never get to the speed of light itself, only close. If you look at the equations, when V=C, the terms for M (mass) go to infinity, so, best case, you’re getting to 99%, not 100%.
The next is that the faster you go, the more that time dilates so that you still see light coming at you at C.

 

[JimPghPA]

Rod Sterling, where are you?

I think we just entered the Twilight Zone.

 

[Astro14]

But if you are traveling away from a source of light at the same speed it is traveling at you, how can it reach you?

By the same token, if you are traveling AT the same light source, it's coming at you at a combined double the speed.

A bit like that whole deal of a 12" ruler only being 6" long as it sped by you at half the speed of light.

Speed is a function of distance over time - that is what Brian Cox was trying to say.

So, the light is not coming at you at a combined double speed, first because you are not going at 100% the speed of light, you are going at some fraction. And your perception of time depends completely on that fraction, so, for you, at 99% C, you see the light blue shifted, but it is still traveling at C because your measure of time over distance is so altered by your velocity.

When time itself changes for you, then what you see as distance, and velocity, are going to be different.

For the person standing on the road next to you, watching your relativistic car go by, and watching the light from, say, the headlights of another relativistic car coming the opposite direction on your super speed highway, the light from both headlights appeared to be going the speed of light. Both cars appear to be going very close to the speed of light.

And, importantly, for both observers in each of the cars, the light from headlights on the other car appeared to be going the speed of light.

 

[PandaBear]

But if you are traveling away from a source of light at the same speed it is traveling at you, how can it reach you?

By the same token, if you are traveling AT the same light source, it's coming at you at a combined double the speed.

A bit like that whole deal of a 12" ruler only being 6" long as it sped by you at half the speed of light.

Speed of light is not behaving in the same way as Newtonian physics like our cars and planes (our Newtonian physics is just a good estimate based on human observation, close enough for slow poke like us usually).

Speed of light doesn't change regardless of where is it shot out and observed, it is always C = 3x10^8 m/S (or something like that? I forgot). When you travel at speed of light and send another object to travel at speed of light, it is still traveling at speed of light, but it is observed with different timing so that you will observe time differently. This is how all these time dilations work, and why we have twin paradox of space traveler.

Also objects with mass is nearly impossible to reach speed of light because the amount of energy to reach faster speed goes 4x when speed goes 2x, you can get close but will still never reach speed of light even if you put the entire universe's energy to reach it.

Speed doesn't change and time change, so the amount of pulses per second change, which is color shift as Astro said.

 

[kschachn]

Speed of light is not behaving in the same way as Newtonian physics like our cars and planes (our Newtonian physics is just a good estimate based on human observation, close enough for slow poke like us usually).

Speed of light doesn't change regardless of where is it shot out and observed, it is always C = 3x10^8 m/S (or something like that? I forgot). When you travel at speed of light and send another object to travel at speed of light, it is still traveling at speed of light, but it is observed with different timing so that you will observe time differently. This is how all these time dilations work, and why we have twin paradox of space traveler.

Also objects with mass is nearly impossible to reach speed of light because the amount of energy to reach faster speed goes 4x when speed goes 2x, you can get close but will still never reach speed of light even if you put the entire universe's energy to reach it.

Speed doesn't change and time change, so the amount of pulses per second change, which is color shift as Astro said.

Well it’s always c but not always that value.

And it’s not “nearly impossible” for a massive object to reach the speed of light, it’s just plain impossible.

 

[Passport1]

So after all that, what is the speed of dark?

 

[billt460]

So after all that, what is the speed of dark?

That brings up another hard to understand pitch...... Space is infinite and endless...... Everything else has a life. A beginning and a end..... Except space. It goes on forever.

 

[ripcord]

yep, the faster you drive, the more time you have.

Relatively