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Im doing my science fair project on time dilation, and I am wondering how to prove that the speed of light is absolute.

Can anyone help me?

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- Thread starter Gigahurtz
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- #1

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Im doing my science fair project on time dilation, and I am wondering how to prove that the speed of light is absolute.

Can anyone help me?

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DaveC426913

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So, the logic is thus:

Let's

Then ...

Thus etc., etc. etc...

And we arrive at Einstein's theory of relativity.

So,

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jtbell

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Not even that. It is a postulate that, as far as we can tell (see post #4), is completely consistent with nature.I'm not sure youcanprove it. It's a postulate.

Purely conjecturally (I am not espousing a crank theory!), suppose someone experimentally finds a very slight frequency-based dependency in the speed of light and others confirm the results. While Einstein's postulate will remain an interesting mathematical postulate, it will be in contradiction with how the universe truly works. Einstein's postulate will be deemed as approximately correct.

One can prove things in mathematics. Science doesn't work that way. After seeing thousands of black crows, and never seeing a crow other than black, you might postulate that all crows are black. Scientists worldwide confirm your hypothesis. This does not prove your hypothesis is correct. It will in fact be provably incorrect the minute someone documents finding an albino crow.

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Born2bwire

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Being in 8th grade not all of those will probably be something you will want to look at or understand. Still, there are a few that I would suggest looking at in detail. The first would be the Michelson-Morley experiment. This experiment was an important result against the prevailing ether theory of the propagation of light. The experiment showed that the speed of light is invariant to the frame of motion of the Earth. If there was an ether or some fluid through which light propagated, then the motion with respect to the fluid would affect the speed of propagation.

A more modern example in terms of special relativity that I would suggest is particle physics. Like Cantab stated, there are none decay times and half-life of particles which we can compare against in particle accelerators. In an accelerator, the particles produced will travel at relativistic speeds, allowing us to observe time dilation by comparing how long the particles lasted at high speeds with respect to how long they last at rest. I once had a workbook in high school of bubble chamber photos. Using overlays, you could measure the curvature of a path to find the energy and type of particle. You could measure the length of the path and using the energy try to deduce the lifetime. A fun and surprisingly accurate exercise but I do not know what the name of the text was.

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Fredrik

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It is. Welcome to Physics Forums.I'm in grade 8, but this website looked really helpful

You don't. What you're talking about is a part of the definition of special relativity, which is a scientific theory. Theories can't be proved. Consider e.g. the theory that keys fall towards the ground when dropped from a human hand. It's a valid theory because it makes testable predictions. To prove this theory, you would have to prove all of its predictions, but no matter how many experiments you perform, the theory is always making a prediction that you haven't proved yet. (Dropping the same key a million times doesn't prove that it will fall theIm doing my science fair project on time dilation, and I am wondering how to prove that the speed of light is absolute.

Instead, scientific theories are tested by trying to

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If you know of anything else I could put in my science fair j(on time dilation), it would be very helpful.

I have heard of the Dopler effect, and how that is used in police radar, the red shift/ blue shift.

Would this have any consequence with this question?

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What are some experiments that you would recommend?

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russ_watters

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There's a definition issue here that I think gives the wrong impression. The word "prove" covers a range of levels of verification and does not automatically imply an absolute. The words "evidence" and "proof" are exactly synonomous with each other and so every time you do a successful experiment, you've done more than just not proven it wrong, you've added to the body of proof - you've increased the level to which you can say the theory is "proven". The word "prove" or "proven" shouldYou don't. What you're talking about is a part of the definition of special relativity, which is a scientific theory. Theories can't be proved.

...in math, however, a theorem is either true or false: 100% proven or 0% proven.

...and in the wiki for theory, they quote the National Acadmy of Sciences, and though they don't use the word "proof", they do say "well established". And that's exactly synonomous with "well proven".

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Fredrik

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I don't know much about the experiments myself, but the link that jtbell posted above looks like a good start.What are some experiments that you would recommend?

Another thing you might want to include is the following very easy* proof that invariance of the speed of light implies time dilation: Imagine a train moving at speed v with a laser attached to the ceiling, aimed straight down. The laser is switched on, and hits the floor a time t

This means that you can draw a right triangle such that the lengths of its sides are "the distance the light moved in the train's rest frame", "the distance the light moved in the ground's rest frame" and "the distance that the train moved". If you express those distances in the form "velocity*time" (as I did above), you can use the pythagorean theorem to find the relationship between t and t

*) Very easy for those of us who spent years studying physics at the university, but probably not so easy but still doable for an 8th grader.

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Fredrik

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I agree with a lot of what you said, but I don't think many people consider those wordsThe words "evidence" and "proof" are exactly synonomous with each other

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HallsofIvy

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atyy

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http://physics.weber.edu/schroeder/mrr/MRR.html

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