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

[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.

 

[Doc Al]

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

I still don't understand what you mean by "appears". I can only assume you mean to contrast "appears contracted" with "really is contracted".

Note that Tom does not say the rod "appears" contracted, he says "If a rod is moving, then it is smaller than it is in its own rest frame." (Emphasis mine.)

Perhaps we are arguing semantics, but I think it's important. An analogy: You look into a spherical mirror, your image is distorted. Is the distortion real or apparent? I assume you would agree that you only appear distorted due to how the mirror reflects light. On the other hand, what if I wish to measure the length of my desk? I apply a ruler and get a certain number of centimeters. Is the length of my desk the actual length (in my rest frame, of course) or is it just the apparent length? Again I assume you would agree that it makes sense to say that the measured length is the actual length, not just an illusion or a trick of light.

Now of course there are practical difficulties in measuring the length of desk that is moving past you at an appreciable fraction of light speed--but let's do the thought experiment anyway. Pretend we have incredibly accurate clocks and detectors. We arrange to measure the position of each end of the moving desk at a precise instant of time according to our (stationary) clocks and metersticks. This is what I mean by the measuring the length of the moving desk. We find that its length is smaller compared to what it would measure if it were at rest. I see no justification for saying that the length of the desk merely "appears" smaller: by any normal definition of "length" it really is smaller.

This contraction is a property of space-time; there is no physical force that reaches out and compresses the desk. But it is real nonetheless.

 

[pervect]

I still don't understand what you mean by "appears". I can only assume you mean to contrast "appears contracted" with "really is contracted".

This discussion is starting to get a bit philosophical, but I thought I'd trhow in my $.02, in the hope that it well help more than confuse the issue (we'll have to see how it works out).

If one defines a "real" property of a body as a property that does not depend on the observer, one that is intrinsic only to the body itself, then space and time both fail to be "real" properties. The Lorentz interval, however, which is a mathematical combination of both space and time, does not fail this test, so it qualifies as "real".

This puts space and time in an interesting philosophical situation. Neither one is "real" by itself, but when combined properly, they form a "real" entity.

So one might say that space and time are illusions, as many mystics have done. And to some extent this is correct. On the other hand, it's a bit hard to explain how two illusions, combined together, form something that is real, if one takes this philosophical approach.

Fortunately, however, it usually doesn't matter which quantites one considers to be "real" when doing physics. I will note, however, that it's generally easier to avoid making mistakes by focusing on the quantites which don't change (are invariant) when doing calculations. In relativity, this approach would be to focus on the Lorentz interval.

 

[quantumdude]

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

The rod is shorter than its proper length in the moving frame.

How many times are you going to make me say it?

 

[Nenad]

This discussion is starting to get a bit philosophical, but I thought I'd trhow in my $.02, in the hope that it well help more than confuse the issue (we'll have to see how it works out).

its not philosophical at all. Its Special Relativity.

 

[h8ter]

The rod is shorter than its proper length in the moving frame.

I thought it had proper length in the moving frame. To an outside observer it is shorter. Relative to it's own frame, the rod is proper length.

 

[quantumdude]

I thought it had proper length in the moving frame.

The rod is its proper length only in a frame that is at rest relative to the rod. When I say that the rod is shorter "in the moving frame", I mean that the rod is moving, and the observer who measures the length is watching it go by.

To an outside observer it is shorter. Relative to it's own frame, the rod is proper length.

That's right.

 

[h8ter]

Ok, I see what you were saying now. I probably just have poor reading comprehension skills.

 

[bino]

the rod is shorter when it is moving but only to the at rest observer. but if we are going the same speed as the rod then we know that it is not actually shorter.

 

[Nenad]

the rod is shorter when it is moving but only to the at rest observer. but if we are going the same speed as the rod then we know that it is not actually shorter.

Be carefull with the word 'actually'. If you do enter the frame of reference of the rod (light speed), you lill measure it to be rest length, but it you do not enter its frame, and you are at rest while iti s moving, the rod is then 'actually' shorter, meaning it is shorter.

 

[quantumdude]

the rod is shorter when it is moving but only to the at rest observer. but if we are going the same speed as the rod then we know that it is not actually shorter.

What is it with you?

DocAI just described how the measurement process would be carried out. You simultaneously record the locations of the endpoints of a rod as it moves by, and subtract the coordinates. The distance between the points is the length of the rod, and that distance varies with speed.

Haven't you looked at that textbook yet?

 

[bino]

if a ship travels from Earth moving at .99c to a destination 44000 lightyears away. from the view of the ship the trip would take 6270 years but from the view of Earth it would take 44468 years. but from the view of the ship the Earth would be moving at .99c. then wouldn't those numbers be switched?

 

[quantumdude]

if a ship travels from Earth moving at .99c to a destination 44000 lightyears away. from the view of the ship the trip would take 6270 years but from the view of Earth it would take 44468 years. but from the view of the ship the Earth would be moving at .99c. then wouldn't those numbers be switched?

No, because the distance between the Earth and the destination is shorter in the ship frame.

 

[bino]

i have no problem saying that the length of the ship will be measured shorter. i completely agree with that. but the length is not physicaly getting smaller.

 

[quantumdude]

i have no problem saying that the length of the ship will be measured shorter. i completely agree with that. but the length is not physicaly getting smaller.

At last, something I can agree with!

The rod is not physically getting smaller--it simply is smaller than it is in its rest frame.

 

[bino]

right
like i said earlier

you have to keep in mind that the length contracts only from the point of view of the stationary object. that's where the disagreement comes from. the ship looks shorter because it is shorter from the point of view of the lattes. the measurements from the equipment are correct from their point a view. the measurement are taken from a point in time. at that point in time the ship will measure to be shorter than its real length. but from the point of view of the ship its length has not changed so the equipment on the ship will say that same thing that it is in fact the same length as when it was stopped. it all matters on the point of view.

onward and forward.

the ship moving at .99c, 44000 lightyears away. and the Earth moving at .99c, 44000 lightyears away. those are the same, the only difference is what is moving from each others perspective.

 

[Doc Al]

the ship moving at .99c, 44000 lightyears away. and the Earth moving at .99c, 44000 lightyears away. those are the same, the only difference is what is moving from each others perspective.

Not true. The two frames will disagree as to the distance, since they are in relative motion.

 

[bino]

i don't mean that they are moving at the same time. sorry. i mean that the ship moving away from Earth is the same as the Earth moving away from the ship.

 

[quantumdude]

right
like i said earlier


onward and forward.

the ship moving at .99c, 44000 lightyears away. and the Earth moving at .99c, 44000 lightyears away. those are the same, the only difference is what is moving from each others perspective.

No, and I already answered that:

No, because the distance between the Earth and the destination is shorter in the ship frame.

 

[pervect]

its not philosophical at all. Its Special Relativity.

Guess my remarks didn't resolve much.

A statement about what is "actually" happening or what is "really happening" tends to be a sign that a philosophical discussion is occurring.

Generally, philosophy is pretty harmless (except for being a potential source of undending debate), and it usually doesn't matter what one thinks is "real", and what one thinks is "appearance". There are a few exceptions, basically they occur when someone does philosophy badly.

An example of bad philosophy would be to insist that lengths don't change with motion, because of some philosphical belief about them being real.

Another example of bad philosophy would be to claim that time and space are illusion, and then to turn around ans inconsistently start talkig about the "true" length, or the "real" time.

 

[bino]

i don't understand how they could be different? one is going .99c for 44000 lightyears while the other is at rest. and the same goes for the other.

 

[quantumdude]

i don't understand how they could be different? one is going .99c for 44000 lightyears while the other is at rest. and the same goes for the other.

The distance between Earth and destination is different for the two observers for the exact same reason the length of a rod is different in different frames: Length contraction.

Look at the Lorentz transformation, and you can derive it for yourself.

 

[Nenad]

hey bino, how many posts do you have on this thread, like 80? lol. Just read the book Tom posted for you earlier, then come with the questions.

 

[bino]

i understand that

The distance between Earth and destination is different for the two observers for the exact same reason the length of a rod is different in different frames: Length contraction.

what i don't understand is in the point of view from the Earth the ship is moving but in the point of view from the ship the Earth is moving. right? so then from the point of view of the ship the Earth would then take 44468 years to go 44000 lightyears. and from the point of view from the Earth the trip only took 6270 years.

 

[Nenad]

i understand that



what i don't understand is in the point of view from the Earth the ship is moving but in the point of view from the ship the Earth is moving. right? so then from the point of view of the ship the Earth would then take 44468 years to go 44000 lightyears. and from the point of view from the Earth the trip only took 6270 years.

no, in both points of wiew, it takes the other 6270 years to do the trip, but one of them is wrong. The person in motion is wrong and finds out he is wrink when the ship stops.

 

[bino]

ok let's think about it this way.

the starting point =
a b
< >

a< --------------------- >b
resting 44000lightyears moving

from the point of view of a, b has moved 44000 lightyears away at .99c.

now back to start =
a b
< >

a< --------------------- >b
moving 44000lightyears resting

from the point of view of b, a has moved 44000 lightyears away at .99c.

how is that not the same?