The discussion centers on the concept of proving the constancy of the speed of light, particularly in relation to time dilation and Einstein's theory of relativity. Participants emphasize that scientific theories, including the speed-of-light postulate, cannot be definitively proven but can be supported through experimental evidence. Key experiments mentioned include the Michelson-Morley experiment, which demonstrated the invariance of light speed, and particle physics experiments that observe time dilation effects in high-speed particles. The conversation highlights the importance of understanding scientific theories as frameworks for making predictions rather than absolute truths.
PREREQUISITESStudents, educators, and anyone interested in physics, particularly those studying the principles of relativity and the nature of light.
Not even that. It is a postulate that, as far as we can tell (see post #4), is completely consistent with nature.DaveC426913 said:
jtbell said:
It is.Gigahurtz said:
Welcome to Physics Forums.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 the next time, but the theory predicts that it will).Gigahurtz said:
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" should always come with a qualifier that specifies a standard. Ie, when a jury determines someone's guilt is proven, it isn't an absolute, but is "beyond a reasonable doubt". Though there is no specific similar standard in science, you can judge the relative strength of individual theories as, say, 50% proven, 90% proven, etc., even while knowing there is no such thing as 100% proven...Fredrik said:
I don't know much about the experiments myself, but the link that jtbell posted above looks like a good start.Gigahurtz said:
I agree with a lot of what you said, but I don't think many people consider those words exactly synonymous. You mentioned that the courts define "proof" with the words "beyond resonable doubt", but I've heard that law students are taught that "evidence" is anything that changes the probability that a given statement is true. For example, if you have a good reason to think there's a 22% probability that statement X is true, and you find something that gives you a good reason to change that to 24%, that's "evidence" of X (and if what you found changed the probability to 21%, that's evidence against X).russ_watters said: