A Good Light

I wish all my students well in their final physics exam this year. Classes ended today with a session on Special Relativity. One bright student really surprised me with the remark, “Yes, but the speed of light is slowing down, isn’t it?” I thought it best to ask her exactly what she meant by that, and she replied enthusiastically that her Dad (a school science teacher) had told her that we now have evidence that the speed of light has been slowing down. I carefully pointed out that, yes, indeed, there were physicists willing to contemplate this evidence with a critical and fair eye, but that the vast majority would entirely disagree with the idea. She said, “Yes, but Relativity is only correct until it is shown to be wrong, right?” I pointed out that, yes, a physical theory only had a certain domain of applicability, beyond which it would not apply, and she said, “Well, we’ve seen that already with Newtonian mechanics!” And it was true that I did have to work hard this week explaining that Newtonian clocks simply didn’t work when things started moving at high speeds, so I confessed that I was actually personally fond of the idea of a slowing speed of light, until another student impatiently drew me back to the problems in hand.

3 Responses so far »

  1. 1

    Anonymous said,

    “we now have evidence that the speed of light has been slowing down.”

    Wish you would say what the facts are, what evidence, etc.

  2. 2

    L. Riofrio said,

    Hooray! Now what we have been advocating is starting to filter down to the schools, so that Kea didn’t need to tell the student first.

    “Yes, but Relativity is only corrct until it is shown to be wrong, right?”

    She sounds like a student to watch out for, already thinking for herself. I am curious just where she and her Dad found out about evidence that c is slowing.

  3. 3

    Pioneer1 said,

    I had the same thought. Are we seeing a change due to the Internet? Maybe flow of information in physics will be better.

    A couple of questions to speed of light experts:

    If the speed of light is slowing down in rarified media, it should also slow down in, say water, or crystals. Are there any experiments to confirm this?

    How do we know that speed of light is getting slower instead of the medium getting less rarified?

    And if the speed of light is slowing down does this mean that it is no longer independent of the speed of the source?

    Just curious. Thanks.

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