Can the Speed of Light Be Changed and What Does It Mean for Space Exploration?

[Nenad]

6270y = t\sqrt{1 - 0.99c^{2} /c^{2}}
6270y = t\sqrt{1 - 0.9801c^{2} /c^{2}}
6270y = t\sqrt{1 - 0.9801}
6270y = t\sqrt{0.0199}
6270y = t(0.141)
\frac {6270y}{0.141} = t
t = 44468 years

 

[bino]

what is lights relativistic mass?

 

[bino]

6270y = t\sqrt{1 - 0.99c^{2} /c^{2}}
6270y = t\sqrt{1 - 0.9801c^{2} /c^{2}}
6270y = t\sqrt{1 - 0.9801}
6270y = t\sqrt{0.0199}
6270y = t(0.141)
\frac {6270y}{0.141} = t
t = 44468 years

got yeah! that makes sense.

 

[Nenad]

listen, bino, I am not going to sit here and spoonfeed you all night, look it up on a google search, or on another forum. Trust me, its a lot better than asking me 1000 questions and its a lot faster. Sorry for the outburst.

 

[Doc Al]

Assuming that you are going at o.99c. In Earth's point of view, they will see your trip takes:
t_o = t\sqrt{1 - v^{2} /c^{2}}
6270y = t\sqrt{1 - 0.99c^{2} /c^{2}}
\frac {6270y}{0.141} = t
t = 44468 years

Perfectly correct, of course, but the simplest way to look at it from the Earth's viewpoint is t = D/v = 44000/0.99{ yr} = 44400{ yr}.

 

[quantumdude]

Bino,

Physics is best learned by working out problems. You're obviously curious and interested, and I think you'll benefit from this:

Special Relativity

It's an excellent textbook in relativity, and it's free.

 

[bino]

ok hypothetically, if i were in a ship that was going the speed of light. how long would it take to get to that star 44000 lightyears away? from the point of view of the ship.

 

[quantumdude]

ok hypothetically, if i were in a ship that was going the speed of light. how long would it take to get to that star 44000 lightyears away? from the point of view of the ship.

It wouldn't take any time at all from that point of view. As Einstein said, the speed of light plays the role of an infinitely great speed in SR.

 

[bino]

how is it that we can measure the speed of light if it doesn't take any time for it to get from one place to another?

 

[Chronos]

how is it that we can measure the speed of light if it doesn't take any time for it to get from one place to another?

It does take time for light to travel any distance, unless you are a photon. In which case time and space cease to exist. Ordinarily, I would ask what part of relativity do you not understand. In this case, I would say the answer is all of it.

 

[what_are_electrons]

This thread seems to contain a lot of hypthetical ideas akin to theories. How has it survived? Perhaps the speed of our Mentors has dropped out of light speed.

 

[ArmoSkater87]

light has no rest mass. It has relativistic mass, and momentum.

Actually light can't have relativistic mass because of SP equations...
m = \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}

As you can see, if something has a rest mass(m_0) of zero, then the relativistic mass is zero as well because zero divided by anything is zero.

It wouldn't take any time at all from that point of view. As Einstein said, the speed of light plays the role of an infinitely great speed in SR.

Lightspeed is a constant finite speed, I thought this was the basis of SR.

Or is it because this...
u' = \frac{u+v}{1-\frac{uv}{c^2}}
The light from the star coming towards u at c, and you going towards it at c

u' = \frac{c+c}{1-\frac{c^2}{c^2}}
u' = \frac{2c}{0}
u' = infinity

 

[quantumdude]

This thread seems to contain a lot of hypthetical ideas akin to theories. How has it survived? Perhaps the speed of our Mentors has dropped out of light speed.

Those who are politely asking questions are being accommodated.

Those who are rudely making unscientific assertions have been banned.

Does that answer your question?

 

[quantumdude]

Lightspeed is a constant finite speed, I thought this was the basis of SR.

Or is it because this...
u' = \frac{u+v}{1-\frac{uv}{c^2}}
The light from the star coming towards u at c, and you going towards it at c

u' = \frac{c+c}{1-\frac{c^2}{c^2}}
u' = \frac{2c}{0}
u' = infinity

No, that's not an equation of relativity (if you're adding in the numerator, you should adding in the denominator, and the same goes for subtracting).

"c" plays the role of an infinite velocity because it is unattainable.

Actually, while the above statement is true, I shouldn't have said that it "takes no time at all" for light to travel a distance, because SR actually makes no predictions about what happens at light speed. So I officially withdraw that comment.

 

[quantumdude]

how is it that we can measure the speed of light if it doesn't take any time for it to get from one place to another?

You have to be careful. I said that "it takes no time at all", meaning that it takes no time in the reference frame of the light. In the lab frame however, it takes a finite time, and the speed of a light pulse is easily measured by recording the position of emission, the position of detection, and the time interval between those two events.

But as I just said to Armo, I should not have said that "it takes no time at all" in the photon frame, because SR actually makes no predictions on the experimental results obtained from the photon frame. The time it takes to traverse a distance is actually undefined.

 

[bino]

ok. from the view point of the lattes the ship has compressed because the ship is moving so fast, but from the view point of the ship the lattes is the one that is going by so fast and that is why the lattes is compressed. correct? so then from the view of light we would be moving that fast. so then from the frame of light we would be compressed. how can this be?

 

[Nenad]

? Read the book posted a while ago about special relativity. It helps a lot. If thwo abjects are in the same frame of reference, (travelling at the same speed in the same direction) then they see no difference in themselves. There is no dilation or compression.

 

[quantumdude]

ok. from the view point of the lattes the ship has compressed because the ship is moving so fast, but from the view point of the ship the lattes is the one that is going by so fast and that is why the lattes is compressed. correct?

Not really. I kept saying before that nothing actually happens to either the ship or the rod. It's not as if some physical force is pushing on them to cause them to be shorter. They simply are shorter in other frames of reference.

so then from the view of light we would be moving that fast. so then from the frame of light we would be compressed. how can this be?

As I said, SR makes no predictions about what would be seen from an inertial frame moving at speed c. The Lorentz factor is undefined there. We can talk about things that happen in inertial frame as its speed approaches c, but if you want to keep talking about frames that move at the speed of light, then SR has no answers for you, and so neither do I.

Now if you want to talk about frames moving with speeds less than c, we can get somewhere.

 

[bino]

but from the frame of reference of the light we would be the ones moveing at the speed of light. right? you know when your driving in a car the objects closer tothe car look like there are moving faster than the objects farther away. idont remember what that's called but why doesn't that have an effect on the Lorentz equation?

 

[russ_watters]

but from the frame of reference of the light we would be the ones moveing at the speed of light.

bino, Tom just said under SR, there is no such thing as "the frame of reference of the light."

 

[bino]

i know what he said. its just that there has to be a frame of reference for light. that is what i don't understand.

 

[Nenad]

when traveligna th the speed of light, mass becomes infinite, time becomes 0, and distance becomes 0. So in essence, you are everywhere and anywhere in the universe at once. This is why it is hard to talk about lights frame of reference. Do you understand now.

 

[quantumdude]

i know what he said. its just that there has to be a frame of reference for light. that is what i don't understand.

There isn't a reference frame for light. That is, there is no frame in which light can be considered at rest. As I noted earlier, and as Einstein himself noted in his original paper, c plays the role of an infinite speed in SR.

when traveligna th the speed of light, mass becomes infinite, time becomes 0, and distance becomes 0. So in essence, you are everywhere and anywhere in the universe at once.

You have to be a bit careful when talking about what happens at light speed. This is the same mistake I made earlier when I got careless and said that it "takes no time at all" for a photon to travel a distance, from it's own frame. The reason this is not right is that the Lorentz factor has a "zero denominator" when v=c. SR literally makes no prediction about what happens at v=c, because the Lorentz transformation is undefined there.

 

[bino]

is it that there in on frame of reference for light or is it that we just don't have equation to predict lights frame of reference? and what about this?

you know when your driving in a car the objects closer tothe car look like there are moving faster than the objects farther away. i don't remember what that's called but why doesn't that have an effect on the Lorentz equation?

 

[Doc Al]

is it that there in on frame of reference for light or is it that we just don't have equation to predict lights frame of reference?

According to special relativity there is no possible reference frame for light.

and what about this?

you know when your driving in a car the objects closer tothe car look like there are moving faster than the objects farther away. i don't remember what that's called but why doesn't that have an effect on the Lorentz equation?

The effect you describe here is an optical illusion called the "parallax effect". It has no bearing on the Lorentz transformations, because those equations relate actual measurements not just how things "appear". The predictions of relativity are real effects, not just illusions of perception.

For more information on the parallax illusion, see this: http://www.campusprogram.com/reference/en/wikipedia/p/pa/parallax.html

 

[Alkatran]

Light moves relative to everything at c. Light moves relative to itself at c. But since light has no time...

It's all very confusing, non-logical, random, lalalala... you know all that fun stuff that happens when you divide by 0.

 

[bino]

we astablished in earlier conversation that neither the ship nor the lattes are actually getting smaller that they only appear to be getting smaller from each others view. and with parallax all objects move backward relative to the car, and for nearby objects the speed of change in direction is what the observer considers the normal consequence of his own movement; however, for distant objects the backward change in direction is slow and much less obvious than the forward change in direction relative to nearby objects. It seems as if distant objects move a little slower. it seems that it should have an effect.

 

[Chronos]

we astablished in earlier conversation that neither the ship nor the lattes are actually getting smaller that they only appear to be getting smaller from each others view. and with parallax all objects move backward relative to the car, and for nearby objects the speed of change in direction is what the observer considers the normal consequence of his own movement; however, for distant objects the backward change in direction is slow and much less obvious than the forward change in direction relative to nearby objects. It seems as if distant objects move a little slower. it seems that it should have an effect.

Try reading this and see if it helps. It gives a nice history of physics leading up to relativity, the problems earlier researchers encountered, and how relativity solved them.
http://www.mathpages.com/rr/s2-05/2-05.htm

 

[Doc Al]

we astablished in earlier conversation that neither the ship nor the lattes are actually getting smaller that they only appear to be getting smaller from each others view.

I don't know what you mean by "appear". You seem to think that the SR length contraction is an optical illusion in the same sense that the parallax effect is. Not true. All measurements of objects will confirm that they actually do have a shorter length when observed from a frame in which they are moving. They don't just appear to be shorter; in the moving frame they are shorter.

On the other hand, if you mean that the length of a ship in its own rest frame doesn't change just because a moving observer happens to pass by: That's certainly true! (SR is strange, but not that strange.)

and with parallax all objects move backward relative to the car, and for nearby objects the speed of change in direction is what the observer considers the normal consequence of his own movement; however, for distant objects the backward change in direction is slow and much less obvious than the forward change in direction relative to nearby objects. It seems as if distant objects move a little slower. it seems that it should have an effect.

Parallax, on the other hand, is just a perceptual illusion. Nearby objects merely appear to go by faster compared to background objects. But clearly the actual speed of the objects with respect to you does not depend on the angle of view. Once you understand what causes the parallax illusion, you can account for it. The SR effects depend only on the actual speed, so parallax has no effect.

 

[bino]

The object isn't "getting smaller". If a rod is moving, then it is smaller than it is in its own rest frame. But nothing actually happens to the rod. It's not as though the rod is physically shrinking by some compressive force.

therefor it just appears contracted from the view of the object at rest.