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*sort of*like an antimatter particle going backwards in time."

What did he mean by "sort of"?

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- Thread starter Unredeemed
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What did he mean by "sort of"?

- #2

mathman

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- #3

Vanadium 50

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It was my last lesson yesterday and I intend to ask him on monday, but I was wondering if I could find an answer here first.

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HallsofIvy

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When your straightedge meets the central "V" of the "M", two new particles magically appear out of nowhere! That is a "creation pair"- a particle and its anti-particle, an electron and a positron. Now continue moving the straight edge up the paper. You now have two pairs of particle moving toward each other, one pair on the left, the other on the right. When you finally reach the two "/\" points of the "M" those two pair disappear: an electron and a positron have annihilated each other. The electron that was originally on the left has annihilated the positron that was created in the middle and the electron that was created in the middle has annihilated the postitron that was initially on the right.

Now lift your straightedge and look at the "M" itself. Do you see that you can think of that a single track: as an electron coming in on the left, moving "forward in time" then suddenly is turned "back in time" until, at the "V" it turns "forward in time" again , eventually hits the top "/\" and turns back in time once more. The movement "back in time" is what we, with our limited "one instant" perspective, see as a positron.

You might suspect that it would take some real cataclysm to change motion "forward in time" to "backward in time" and vice-versa. That's exactly right! It is the enormous energy, E= mc

I have no idea how "serious" Feynman was when he proposed this but it does answer one basic question: All electrons are identical because there's really only one electron, bouncing back and forth in time!

- #6

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When your straightedge meets the central "V" of the "M", two new particles magically appear out of nowhere! That is a "creation pair"- a particle and its anti-particle, an electron and a positron. Now continue moving the straight edge up the paper. You now have two pairs of particle moving toward each other, one pair on the left, the other on the right. When you finally reach the two "/\" points of the "M" those two pair disappear: an electron and a positron have annihilated each other. The electron that was originally on the left has annihilated the positron that was created in the middle and the electron that was created in the middle has annihilated the postitron that was initially on the right.

Now lift your straightedge and look at the "M" itself. Do you see that you can think of that a single track: as an electron coming in on the left, moving "forward in time" then suddenly is turned "back in time" until, at the "V" it turns "forward in time" again , eventually hits the top "/\" and turns back in time once more. The movement "back in time" is what we, with our limited "one instant" perspective, see as a positron.

You might suspect that it would take some real cataclysm to change motion "forward in time" to "backward in time" and vice-versa. That's exactly right! It is the enormous energy, E= mc^{2}, necessary to create an eletron-positron pair or given up when such a pair annihilates.

I have no idea how "serious" Feynman was when he proposed this but it does answer one basic question: All electrons are identical because there's really only one electron, bouncing back and forth in time!

Thank you very much, that was exactly the kind of answer I was hoping for.

I do however have one question: How do the two new particles "magically appear out of nowhere"?

- #7

malawi_glenn

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vacuum energy, the vacuum has energy in physics.

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vacuum energy, the vacuum has energy in physics.

Oh, so is the "magical" creation of the particles what they call a quantum fluctuation?

- #9

malawi_glenn

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But now I think HallsofIvy was referring to pair creation out of photons.

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I do however have one question: How do the two new particles "magically appear out of nowhere"?

Once you get comfortable with that idea, consider that may also be how our entire universe started....via a random quantum fluctuation!!!! Seems rather crazy, but NOT improbable.

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