Where does energy go during destructive interference?

Re:Where does energy go during destructive interference? by krick on Thursday August 11, 2022 @01:36AM (#32421954)

Huh. It didn't really answer the question for me, but, anyway, now I'm more wondering about how comes that this question never occured to me in my entire life. This seems like the most obvious thing to ask, but I don't remember ever wondering about it.

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Re:Where does energy go during destructive interference? by yetihehe on Thursday August 11, 2022 @02:03AM (#32422108)

Short answer: It gets pushed out in other places.

Long answer: When you try to do destructive interference, you do it only in specific places, you have valleys and peaks somewhere else. Energy from valleys (detructive interference) just enlarges peaks and makes them brighter. As first commenter on that topic said, you can't make destructive interference without making constructive one in different place, so energy is not lost.

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Re:Where does energy go during destructive interference? by dvh on Thursday August 11, 2022 @02:49AM (#32422345)

At uni professor was drawing inverse FFT of impulse response in a filter and he only used first few frequencies and then asked "can anybody see what's wrong with this chart?". We were all silent...

Turns out if you only use first few frequencies of FFT the filter output will look like it respond slightly before the signal arrives. It's a freaking time machine.

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Re:Where does energy go during destructive interference? by xnoreq on Thursday August 11, 2022 @04:46AM (#32423113)

What are you talking about? Do you mean first few frequency bins, and setting the others to zero? That would be a simple linear-phase lowpass filter. And if you do the shifting properly then you will see that it has a positive group delay.

There are filters with negative group delay, however. But FFT is irrelevant for that and it's not a time machine either.

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Re:Where does energy go during destructive interference? by jononor on Thursday August 11, 2022 @04:18AM (#32422925)

Non-causal filters can be quite useful, and can be realized when the entire input sequence is available. And if one puts in a delay line, then can work without needing access to future timesteps.

A bit harder to realize with electronics or mechanics than software though...

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Re:Where does energy go during destructive interference? by dennis-tra on Thursday August 11, 2022 @02:47AM (#32422327)

Same here! I once came across a similar question that asked where energy goes when light red-shifts from distant galaxies.

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Re:Where does energy go during destructive interference? by bl0rg on Thursday August 11, 2022 @01:48AM (#32422030)

Same. I love that feeling.

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