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

[kuenmao]

First of all, I really agree that you should do some reading on special relativity and general relativity before you come back to ask another set of questions.

In reply to your question, first of all, not everything is fixed to the Earth. For example, winds experience forces and move in interesting patterns due to Earth's rotation. That is because the Earth is strictly an inertial reference frame. Since people thought that light was supposed to move at c only when measured at an inertial reference frame, c measured in different directions with respect to the motion of the planet were supposed to have different speeds. That was the whole idea of the Michelson-Morley experiment.
It's like measuring the time taken for a boat to go and come back across a river of width k units, and then comparing the time to the time measured when the boat moves upstream for k units and then downstream. There would be some difference in the times if the water in the river were running.
It doesn't only depends on the rotation of the Earth...it also depends on Earth's orbiting around the sun, and all other accelerating movements of the Earth.
Anyway, relativity explained the results very beautifully.

 

[bino]

"Since people thought that light was supposed to move at c only when measured at an inertial reference frame, c measured in different directions with respect to the motion of the planet were supposed to have different speeds. That was the whole idea of the Michelson-Morley experiment."

their experiment could not do what they thought it would since the whole experiment was moving along at the same speed as the earth. (it would be more like if someone was throwing a ball in a box the ball will be moving at the same speed no matter what direction i throw it in front to back, side to side even if the box was moving.) from the frame of the person in the box.

 

[bino]

It's like measuring the time taken for a boat to go and come back across a river of width k units, and then comparing the time to the time measured when the boat moves upstream for k units and then downstream. There would be some difference in the times if the water in the river were running.

i think i read somewhere that flowing water has an effect on the speed of light also. light moves faster going downstream than it would if it was going upstream or if the water was not flowing. ill try to find out where i read that.

 

[Nenad]

i don't understand how the michelson-morley experiment could have worked in the first place. everything is fixed to the Earth the speed of light could not have changed anyway. how does that have to do with the rotation of the earth?

the reason for the Michelson experiment is to test for an 'ether' that light was supposed to travel through, since it was thought to be a 'wave'. And since the Earth torates around the sun and rotates on itrs axis, it was thought that this ether was raming into it, since it was supposed to be stationary. The point of their experiment was king for like sending a boat upstream and downstream, the ether was like water, so the light should go faster in one direction than in the other.

 

[bino]

ok so then its important because it debunked the ether theory.

 

[bino]

but how does that equate into light being the same speed for all frames?

 

[kuenmao]

It all starts with Maxwell's equations, which predicted light to move at a certain speed c. However, there wasn't any implication of which reference frame we would measure speed at. It seemed as if there was one unique reference frame at absolute rest. That would be the frame which "ether" would exist at.
If ether existed, they would have measured a difference in the speed of light going "upstream, downstream" and "across the river", which is actually just the difference between Earth's reference frame and the "frame at absolute rest". However, they didn't measure any difference.
Einstein solved this problem by suggesting that light perhaps was at the same speed c for all frames, not just one. Nobody know why it is like that, but nowadays it seems that it just explains the phenomena beautifully. However, consequences of SR changes our views and makes classical physics no longer applicable at great speeds.

 

[russ_watters]

but how does that equate into light being the same speed for all frames?

Because ether theooy is what says that light speed is not the same in all frames. If ether theory were correct, then measuring the speed of light traveling east, you'd get C+1000mph, and measuring the speed of light traveling west, you'd get C-1000mph. That's (basically) what the M&M experiment was trying to find.

 

[bino]

right right. but their test was not tested in different frames the whole thing was only in one frame. or is that they thought that the ether was moving around the surface of the earth? because the way I am thinking, they were thinking, is that the ether is going around the outside of Earth's atmosphere.

 

[pervect]

People thought about ether dragging theories for a while, but couldn't reconcile the results with stellar aberration results. If the Earth was dragging the ether around it as it moved, this should have some optical effects on observing stars (depending on the exact variety of theory being used) - no such effects were found.

Of course, nowadays we don't have to rely on the limited experimental results that were available when relativity was first being formulated, we have a whole host of experimental confirmations of relativity. See for instance

http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.htmlhttp://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

For instance, we have measured the speed of "light" (gamma rays) emitted from the decay of fast (.99975) pi mesons with a resolution of 400ppm, and found no change. That's just one of a huge number of experiments.

Modern high particle accelerators wouldn't work at all without relativity - the early cyclotron designs gave way to the synchrotons. GPS wouldn't work the way it does without relativity. These are examples of the large number of "informal" tests of relativity - things that simply wouldn't work if relativity were not true, things that are used every day. With the advent of atomic clocks, some of the predictions of general relativity, formerly of only theoretical interest, are of practical importance. As I mentioned before, the accuracy of the Boulder clock is such that the small relativistic shift in frequency due to it's altitude is about 40x as large as the frequency stability of the clock itself.

 

[Figgy04]

seems like i read somewhere that in some 1999 issue of "Nature" there was an article that said that scientists managed to slow down light by a large factor by using a high density clump of Bose-Einstein condensate...
if this is true, what applications can it have?

 

[quantumdude]

right right. but their test was not tested in different frames the whole thing was only in one frame.

Look at the MMX apparatus. There is a beam of light going in two different directions. So relative to the ether, the two beams should have had two different velocities.

 

[bino]

was the ether sapossed to moving around the surface of Earth or around the atmosphere of earth?

 

[quantumdude]

was the ether sapossed to moving around the surface of Earth or around the atmosphere of earth?

Read Chapter 1 of the book I linked you to. It explains everything.

 

[bino]

i did that's where i got my question from. alls it said was that it was believed that Earth moved through the ether. but it didnt say if it went around the surface or atmosphere of earth? becuase if it went around the surface then they should have figured that they would be able to feel it but if it went around the atmosphere then their experement could not have measured anything. either way it was doomed. and i still don't see how it would prove the speed of light is constant? pervect i looked over the website you posted and it had a lot of experiments that where for and against SR. do you any other sites maybe one that has more discriptions of the experiments.

 

[quantumdude]

alls it said was that it was believed that Earth moved through the ether.

You didn't read it very carefully then. It also said that the two beams were moving perpendicularly to each other. That means that the light beams should have had two different speeds, if the Earth were truly moving through the aether. The book is both specific and quantitative on this point. I honestly don't understand how you could have missed it.

but it didnt say if it went around the surface or atmosphere of earth?

It says that, if the aether exists, then the Earth should be moving through it. It says so explicitly on page 3, middle left column and on page 4, upper right column.

becuase if it went around the surface then they should have figured that they would be able to feel it but if it went around the atmosphere then their experement could not have measured anything. either way it was doomed.

The aether doesn't move around anything. It's an inertial frame!

 

[bino]

if the Earth moves through it then the ether has to either move around the Earth or move through the earth.

 

[bino]

i understand what the apparatus was suppose to do and what it looked like. i don't see how it could be considered a valid test to prove anything.

 

[Nenad]

I suggest somebody end this thread right now. LOCK DOWN.

 

[pervect]

nenad, but don't you like the way bino always replies in one at most two sentences, never uses capital leters, and always asks a question at the end?

 

[Nereid]

i understand what the apparatus was suppose to do and what it looked like. i don't see how it could be considered a valid test to prove anything.

Read Chapter 1 of the book I linked you to. It explains everything.

bino, did you?

 

[quantumdude]

if the Earth moves through it then the ether has to either move around the Earth or move through the earth.

The hypothetical aether does not interact with matter, so the motion of the Earth through the aether does not affect it in any way.

i understand what the apparatus was suppose to do and what it looked like. i don't see how it could be considered a valid test to prove anything.

No, I don't think you do understand what it was supposed to do. When I told you that you should read Chapter 1, I did not mean for you to simply look at the pictures. I meant for you to read the text and follow the math. The aether model makes predictions regarding the MMX, and those predictions were not met.

 

[Alkatran]

You drive up to a four way intersection behind a car which is going the same speed as you. He doesn't stop and neither does a car coming from the other direction. They are both going 40 mph and ram into each other at the midpoint of the intersection.

If they had been going the same direction they wouldn't have hit together, for the same reason you didn't hit into the car in front of you. SO:
If a beam of light is moving in a different direction than another beam of light, it is NOT in the same inertial frame, because they can collide.

 

[Nenad]

bino is just playing dumb, he knows how to read, I say READ THE SR BOOK and stop asking questions which could be answered easily by the book.

 

[pervect]

bino is just playing dumb, he knows how to read, I say READ THE SR BOOK and stop asking questions which could be answered easily by the book.

that's my opinion too, his unique style of capitalization and short two-line responses appears to me to be a calculated style to make him look dumb. in other words i think he's trolling.

 

[bino]

i read up to page 11 in the book i have not had time to read further yet. but i did read all about the m&m experiment. so then the ether was suppose to interact only with the light and has no effect on anything else? that makes sense. but then it still only proves there is no ether.