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

[quantumdude]

So, in other words, when measuring the density of emission and absorption, the amount of time should be included. How can that factor be determined?

You can determine the index of refraction by sending a light pulse in and measuring the speed with which it comes out. The ratio of the speed of light in vacuum (c) to the speed of light in the medium (c') is the index of refraction (n). Simply put, n=c/c'.

Or maybe you're wrong. Just because opinions contradict with the standard model, doesn't make them wrong. You are unable to use the standard model to counter new theories or opinionated ideas.

No, you're wrong, and there's no "maybe" about it. While it's true that one theory cannot be used to falsify another theory, it is also true that experimental evidence can falsify a theory. And Galilean relativity (the only kind in which there is no length contraction) has been falsified experimentally.

Has anything moving at relativistic speeds ever been measured? I'm not saying by equations, but by means of physical rulers. Until then, you are unable to claim it not to be an optical illusion. Just because a formula is derived from the transformation of triangles (might I add the way our eyes measure distances is through triangles...this is not always accurate) does not mean it is necessarily true.

Length contraction has not been measured directly, but the invariance of the speed of light has been, as has time dilation. It is not logically possible for the speed of light to be absolute and for time to not be absolute, and simultaneously have space be absolute.

 

[quantumdude]

if a ship going one direction going 90% c and i was going the opposite at 90% and we fly past each other, what would happen then?

You will observe a length contracted ship go past you at 0.994475c and whose length is contracted from its proper length by a factor of 1/0.43589.

 

[bino]

Each claims that the other is shorter, and that nothing is out of the ordinary with regards to their own length. how can it be that the length of an object can get shorter to someone but not to someone else? i could understand it if it only looks shorter to the observer. it is like looking at a barn from 1ft away and looking at it from 200 ft away. the barn is smaller from farther away.

 

[employee #416]

You can determine the index of refraction by sending a light pulse in and measuring the speed with which it comes out. The ratio of the speed of light in vacuum (c) to the speed of light in the medium (c') is the index of refraction (n). Simply put, n=c/c'.

Heh, first year physics. You use index of refraction in Snell's law to find the angle at which light is bent, right? This can also be interpreted as the angle at which light is absorbed and emitted from the old medium to the new medium?

No, you're wrong, and there's no "maybe" about it. While it's true that one theory cannot be used to falsify another theory, it is also true that experimental evidence can falsify a theory. And Galilean relativity (the only kind in which there is no length contraction) has been falsified experimentally.

Hehe, Tom, you cease to amaze me. Experimental evidence relies on our eyes as a confirmation, right? What our eyes see is not what is really happening. Just because something appears to be shorter, does not make it shorter. The true length is ALWAYS there. Things only appear to not be there. If a color-blind person needed a ruler that was blue and said, "Pass me the green ruler." You know the ruler is blue, but the color-blind person sees it as green, because he can not distinguish between colors. Optical illusion.

Length contraction has not been measured directly, but the invariance of the speed of light has been, as has time dilation. It is not logically possible for the speed of light to be absolute and for time to not be absolute, and simultaneously have space be absolute.

I would seriously argue you on that statement. I would really like to stay being a member on this site. Can you provide me with a link on how time dilation works and how it is derived? Lenght contraction is very well an optical illusion that people view as reality. I'm assuming the same about time dilation, but am fully knowledgeable in that area.

Each claims that the other is shorter, and that nothing is out of the ordinary with regards to their own length. how can it be that the length of an object can get shorter to someone but not to someone else? i could understand it if it only looks shorter to the observer. it is like looking at a barn from 1ft away and looking at it from 200 ft away. the barn is smaller from farther away.

This is how our eyes are at flaw of measuring things. Lorentz transformation relies on the way our eyes measure things. It takes a triangle and transforms it to come up with 4 vectors. Blah blah blah blah. So, Lorentz transformations state that an object's length contracts as it is moving at relativistic speeds. A barn LOOKS smaller when viewed from farther away, but we konw the true length is there, right? Is that not a way of saying our eyes can not measure the true size just as our eyes are unable to measure the true length of things moving at relativistic speeds?

 

[quantumdude]

Each claims that the other is shorter, and that nothing is out of the ordinary with regards to their own length. how can it be that the length of an object can get shorter to someone but not to someone else?

Length contraction is a function of speed. In a frame in which the speed of an object is 0, the length is said to be the "proper length". The reason each observer claims that the other is shortened from the proper length and nothing is amiss with their own dimensions is that each observer regards himself at rest, and the other moving. That is, each observer imputes a nonzero speed to the other, and since length contraction is a function of speed, each observer would measure a shortened length for the other.

Now that's about a fundamental an explanation as anyone can give. If you want to know why this phenomenon of length contraction is a function of speed in the first place, or why it occurs at all, the only answer anyone can give is, "Because that's the way it is".

We happen to inhabit a universe in which there is an ultimate speed limit. Two direct consequences of that are time dilation and length contraction.

i could understand it if it only looks shorter to the observer. it is like looking at a barn from 1ft away and looking at it from 200 ft away. the barn is smaller from farther away.

That's not a very useful analogy, because that's not the nature of relativistic length contraction.

 

[bino]

You will observe a length contracted ship go past you at 0.994475c and whose length is contracted from its proper length by a factor of 1/0.43589.

interesting.

 

[quantumdude]

Heh, first year physics. You use index of refraction in Snell's law to find the angle at which light is bent, right? This can also be interpreted as the angle at which light is absorbed and emitted from the old medium to the new medium?

Yes, the index of refraction of a medium is also the ratio of the speed of light in vacuum to the speed of light in the medium.

Hehe, Tom, you cease to amaze me. Experimental evidence relies on our eyes as a confirmation, right?

No. In fact, relativistic measurements do not involve human senses at all, but rather electronic and mechanical subsitutes. Of course, our eyes read the dials, but that's hardly relevant.

What our eyes see is not what is really happening. Just because something appears to be shorter, does not make it shorter.

If something is measured to be shorter, then it is shorter. Measurements are what tell us what is real.

The true length is ALWAYS there.

No, it isn't. You're stuck in pre-relativistic thinking here. One thing SR teaches us is that there is no preferred frame, and there is no "real" length of objects.

Things only appear to not be there. If a color-blind person needed a ruler that was blue and said, "Pass me the green ruler." You know the ruler is blue, but the color-blind person sees it as green, because he can not distinguish between colors. Optical illusion.

This is an irrelevant argument by analogy. If you want to talk about SR, then why not just stick to SR?

Tom: Length contraction has not been measured directly, but the invariance of the speed of light has been, as has time dilation. It is not logically possible for the speed of light to be absolute and for time to not be absolute, and simultaneously have space be absolute.

416: I would seriously argue you on that statement.

And I would tell you to open a physics book and study, because this is really basic stuff.

I would really like to stay being a member on this site.

Then stop being so arrogant. You have obviously not studied physics, and here you are telling us that you can do our jobs better than we can.

Can you provide me with a link on how time dilation works and how it is derived? Lenght contraction is very well an optical illusion that people view as reality. I'm assuming the same about time dilation, but am fully knowledgeable in that area.

I repeat: In SR, neither length contraction nor time dilation are illusory. Lifeless detectors can be used to measure these effects, and they cannot be tricked the way human minds can.

Here is the original paper by Einstein:

On The Electrodynamics of Moving Bodies

This is how our eyes are at flaw of measuring things. Lorentz transformation relies on the way our eyes measure things. It takes a triangle and transforms it to come up with 4 vectors. Blah blah blah blah. So, Lorentz transformations state that an object's length contracts as it is moving at relativistic speeds. A barn LOOKS smaller when viewed from farther away, but we konw the true length is there, right? Is that not a way of saying our eyes can not measure the true size just as our eyes are unable to measure the true length of things moving at relativistic speeds?

This is completely wrong. The Lorentz transformation has nothing to do with human eyes or optical illusions. It states what is really happening, and all experimental tests of its predictions have come out positive. If you want to be allowed to post here, then you are going to have to stop posting your opinions that are based only on your own incredulity and ignorance.

 

[bino]

yes it is a cheap analogy but if you take a picture of a barn then measured it the barn would still be smaller. the same as if you take a picture of something going near light speed. the object would be smaller.

 

[Nacho]

Bunches of question on light being answered .. I got one!

Light moving through a gravitational field will have its direction of travel changed. Is it proper to say that that light is accelerated?

 

[quantumdude]

yes it is a cheap analogy but if you take a picture of a barn then measured it the barn would still be smaller. the same as if you take a picture of something going near light speed. the object would be smaller.

But it's still irrelevant. We don't measure the lengths of objects by photographing them. We measure the lengths of objects by simultaneously recording the locations of their endpoints in some coordinate system, and subtracting the coordinates.

 

[quantumdude]

Bunches of question on light being answered .. I got one!

Light moving through a gravitational field will have its direction of travel changed. Is it proper to say that that light is accelerated?

From a Newtonian point of view, yes. But from a general relativistic point of view, no. Light follows geodesics, and in GR there is no acceleration along a geodesic.

 

[Nacho]

I understand .. Thanks Tom.

 

[bino]

but wouldn't the end points change as i got closer?

 

[quantumdude]

but wouldn't the end points change as i got closer?

No. They are fixed in space.

 

[bino]

wouldnt they be if i were going faster?

 

[quantumdude]

wouldnt they be if i were going faster?

Wouldn't they be what if you were going faster?

It doesn't matter if you are moving past the barn or not. If you simultaneously record the locations of the endpoints of a rod in your coordinate system, then the difference in coordinates is the length of the barn in your frame.

 

[bino]

wouldnt they still be fixed endpoint?

 

[quantumdude]

wouldnt they still be fixed endpoint?

The location of the endpoints--at the time you made the length measurements--are fixed.

 

[bino]

and if i measured the length from 1ft away then i measured it from 200ft away. the measurements would be different.

 

[bino]

the object is getting smaller right?

 

[quantumdude]

and if i measured the length from 1ft away then i measured it from 200ft away. the measurements would be different.

No, it wouldn't. The measurement of length is a function of the relative speed between the observer and the observed. It has nothing to do with the coordinates of the person doing the observation.

edit to add:

the object is getting smaller right?

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.

 

[bino]

No, it wouldn't. The measurement of length is a function of the relative speed between the observer and the observed. It has nothing to do with the coordinates of the person doing the observation.

edit to add:



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.

that just proves my point neither the ship or the lattes is physically getting smaller.

 

[employee #416]

Proves my point also.

 

[pervect]

Yeah, I think the reason why emission and absorption is not constant is that light is absorbed through different densities. If it is absorbed in a material that has a low density, it will be absorbed less, but pass it through a dense material, and it will be absorbed fast. Emission of the photons occurs as a result of absorption.

Our eyes would see Terrel rotation, not Lorentz contraction.

http://www.math.ubc.ca/people/faculty/cass/courses/m309-01a/cook/terrell1.html

 

[employee #416]

I wasn't even talking about contraction. Nowhere in there did i mention Lorentz transformation. I was talking about emission and absorption of photons and that's strictly it.

 

[pervect]

Or maybe you're wrong. Just because opinions contradict with the standard model, doesn't make them wrong. You are unable to use the standard model to counter new theories or opinionated ideas.

He's not wrong.

When opinions are in opposition to observed facts, especially well-observed facts that have been confirmed by a multitude of observers, the opinions are wrong.

Has anything moving at relativistic speeds ever been measured? I'm not saying by equations, but by means of physical rulers.

We see muons reach the Earth's surface.

This is proof of both time dilation (from our point of view), and the Lorentz contraction (from the muon point of view). Otherwise, muons simply wouldn't be able to reach the Earth's surface.

 

[pervect]

that just proves my point neither the ship or the lattes is physically getting smaller.

The length of an object is not the same for a moving observer and a stationary one.

The phrase "physically getting smaller" is unfortunately ambiguous. Measurements made of a moving object *will* show that it's length contracts.

 

[quantumdude]

that just proves my point neither the ship or the lattes is physically getting smaller.

It does not. Your statement that the ship "is physically getting smaller" implies that something is happening to the ship. That is not the case. The fact of the matter is that there is no single "length of the ship". But in your mind, you are at least tacitly denying this, and so you think that when someone measures a length of the ship that differs from the proper length, that something must have been done to the ship to make it so. But that is not right, because there is in fact nothing special about the so-called proper length, other than the fact that it is the length that is measured when the ship happens to be not moving.

 

[quantumdude]

Proves my point also.

By what twisted logic do you reach that conclusion? Recall that your point was that length contraction is an illusion. Nothing I have said supports that view. Indeed, everything I have said specifically denies it.

 

[employee #416]

Silly Tom! Ok, maybe you were not saying what I thought. All-in-all length contraction is an illusion. Refer to the barn example that bino threw out. The bar up close appears to be normal size, but when you inch away from it, it appears to get smaller. It looses measurement off of height and width from the front view. When you are far away from the barn, it looks fairly small. You know that the true length is not that small. Your eyes are playing tricks on you. Do you agree with that? When something is moving at relativistic speeds, your eyes are unable to measure it anywhere near accurate, so it APPEARS TO CONTRACT, when you know that the true length is still in tact.

 

[quantumdude]

All-in-all length contraction is an illusion.

This is the final time I am going to correct you on this. According to SR, the length of any moving object is really less than the length of the same object when it is stationary. Period.

Refer to the barn example that bino threw out. The bar up close appears to be normal size, but when you inch away from it, it appears to get smaller. It looses measurement off of height and width from the front view. When you are far away from the barn, it looks fairly small. You know that the true length is not that small. Your eyes are playing tricks on you. Do you agree with that?

Yes.

When something is moving at relativistic speeds, your eyes are unable to measure it anywhere near accurate, so it APPEARS TO CONTRACT, when you know that the true length is still in tact.

Wrong. First of all, the two situations are not analogous. The apparent shrinking of an object with increasing distance is a bonafide optical effect. Length contraction in SR is not. Second, I have already told you that this has nothing to do with human eyes or human minds. Lifeless mechanical or electronic sensors would register the result predicted by SR. And third, there simply is no "true length" of any object. The length of an object varies with its state of motion.

 

[ArmoSkater87]

employee, by denying length contraction, you are denying time dilation, and therefore you are wrong because time dilation has been physically measured. Precise atomic clocks have been placed in airplanes and observed after a day of flight and apparently the time had been dilated. Not only that...but the amount of time that was dilated fit the model of time dilation exactly. T = T_0 / sqrt(1-v^2/c^2)

 

[employee #416]

Heh, don't babble to me about what I'm denying and what I'm accepting. In the end, you are right though.

Time contraction is also an illusion. Time only seems slower at high velocities, because our eyes can't measure things as fast as it can moving at non-relativistic speeds. This lag in the eye's calculation gives the illusion that time is running slower. This may not be relevant, but I'll take a stab at it. Turn on a strobe light. How does everything look in motion? Slower than it actually is, eh? Our eyes are tricked. We measure things only if visible. If things go in and out of visiblity the eye measure slower than normal. This is an illusion, but we know that time is the same, right?

How can we rely on equations, that are derived from methods our eyes use for measurements? Our eyes do not measure everything accurately. If something is too fast for our eyes to measure, our eye distorts it. If an object is not moving, our eye is not accurate in measuring any dimension of that object. It's all estimated, until a tool for measuring is pulled out for clarity.

An object has a length of 100cm. It is traveling at relativistic speeds. Let's make that speed .95c. It appears to be shorter or is shorter? I'd go with the former. Length does not just disappear into thin air. The true length will ALWAYS be there. The time experienced by that moving object is the same as a person in a difference reference frame. It just seems slower.

Haha, just saw your post Tom Mattson.

This is the final time I am going to correct you on this. According to SR, the length of any moving object is really less than the length of the same object when it is stationary. Period.

No, I'm going to correct you. It only appears to be shorter. The physical length of an object traveling at relativistic speeds is always there.

By true lenght, I'm referring an object measured while on the ground or table.

Second, I have already told you that this has nothing to do with human eyes or human minds. Lifeless mechanical or electronic sensors would register the result predicted by SR.

They are measruing wrong. No length is lost due to motion. That's just stupid. Magically that length returns when an object is decelerated to non-relativistic speeds. No, it was always there. I'm pretty sure this has to do with the human eye. TRIANGLES! The whole formula is derived from the transformation of triangles. I'm pretty sure if you were to mess with it, you could get at the method the human eye uses to measure things.

Why is it an eye trick? Ok, take an object with two points. The point at the head end is point A, while the point at the back end is point B. This object, at rest, has a length of AB. Give this object a velocity that is non-relativistic, and your eyes notice no drastic affects in measuring the length. Give it relativistic speeds, and your eyes notice a huge difference. When it tries to calculate the distance from A to B it is smaller than what the distance is at rest. When point A crosses the eye, almost immidiately point B crosses the same path A has just crossed. Thus making measurment SEEM contracted. No length contraction is taking place.

This is probably all jumbled up...I have school in 2 hours and I haven't slept, so whatever.

 

[ArmoSkater87]

Time contraction is also an illusion. Time only seems slower at high velocities, because our eyes can't measure things as fast as it can moving at non-relativistic speeds. This lag in the eye's calculation gives the illusion that time is running slower. This may not be relevant, but I'll take a stab at it. Turn on a strobe light. How does everything look in motion? Slower than it actually is, eh? Our eyes are tricked. We measure things only if visible. If things go in and out of visiblity the eye measure slower than normal. This is an illusion, but we know that time is the same, right?

You are not understanding what I am talking about. I mean AFTER the airplanes fly for a day, the clock that was on it is compared to the one that was on the ground. So you are saying when we look at these two clocks next to each other, the difference somehow is an illusion?? Not to mention that the difference magically with illusions fits the model.

How can we rely on equations, that are derived from methods our eyes use for measurements? Our eyes do not measure everything accurately. If something is too fast for our eyes to measure, our eye distorts it. If an object is not moving, our eye is not accurate in measuring any dimension of that object. It's all estimated, until a tool for measuring is pulled out for clarity.

An object has a length of 100cm. It is traveling at relativistic speeds. Let's make that speed .95c. It appears to be shorter or is shorter? I'd go with the former. Length does not just disappear into thin air. The true length will ALWAYS be there. The time experienced by that moving object is the same as a person in a difference reference frame. It just seems slower.

Once again, like Tom said...this has nothing to do with your eyes, we arent the ones observing the length contraction, its the electronic sensors. I guess the sensors are tricked by their sillicon chips right?? We only observe the data from the sensors, or are the computer screens also an illusion that makes us think that there is contraction going on?? Wait, what if you print the data out, I am sure the paper deflects the light in such a way that the numbers printed on the paper change before they enter our eyes. Ahh...those damn illusions, don't you just hate them??

No, I'm going to correct you. It only appears to be shorter. The physical length of an object traveling at relativistic speeds is always there.

By true lenght, I'm referring an object measured while on the ground or table.

Humm...you keep saying this without any actualy evidence or data. Its funny to see you say something that is consistent with all observations is wrong and an illusion, and yet you have nothing to actually support your arguement. And please don't quote again with something that has to do with our eyes and illusions.

They are measruing wrong. No length is lost due to motion. That's just stupid. Magically that length returns when an object is decelerated to non-relativistic speeds. No, it was always there. I'm pretty sure this has to do with the human eye. TRIANGLES! The whole formula is derived from the transformation of triangles. I'm pretty sure if you were to mess with it, you could get at the method the human eye uses to measure things.

Why is it an eye trick? Ok, take an object with two points. The point at the head end is point A, while the point at the back end is point B. This object, at rest, has a length of AB. Give this object a velocity that is non-relativistic, and your eyes notice no drastic affects in measuring the length. Give it relativistic speeds, and your eyes notice a huge difference. When it tries to calculate the distance from A to B it is smaller than what the distance is at rest. When point A crosses the eye, almost immidiately point B crosses the same path A has just crossed. Thus making measurment SEEM contracted. No length contraction is taking place.

This doesn't help your case at all and doesn't counter any part of what Tom said in the quote you quoted. Your argument again has to do with the way the eye sees things, which is not the case. We don't know length contraction is true because we observe with our EYES something moving at relativistic speeds. I mean...WTF? We can't even make out details on a car moving by on a highway...and that's like 60mph, oh soooo relativistic isn't it?!?

Anyways...you can't use "illusions with eyes" as a way to defend your case because your eyes only play a role in reading data on a computer or a piece of paper.

Btw...Tom, take it easy, I know the rage you are feeling from such arguements, I feel the same way.

 

[russ_watters]

Minor nitpick - these two statements contradict each other:

If something is measured to be shorter, then it is shorter. Measurements are what tell us what is real.

...there is no "real" length of objects.

I know what you mean, but I think it may be less confusing to others if the second statement read 'every measured length of objects is "real."' You mean there is no single real length and a bunch of illusions.