Comment by Laremere | Hacker News Reader

Comment by Laremere | Hacker News Reader

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As much as I love Veritasium, I feel the OP video is better than his. Actually doing the experiment is really good, and it honestly feels like he was fishing for another debate like the faster than wind car by giving only a super theoretical and unintuitive explanation. (I don't have any real evidence of that, but it does /feel/ like it.)

I also wonder what would happen if, instead of a setup like this:

  ┏───────light────────┓
  ┕──────battery───────┛

You did something like this:

  ┏──────────────light─┓
  ┃                    ┃
  ┃                    ┃
  ┃                    ┃
  ┃                    ┃
  ┃                    ┃
  ┃                    ┃
  ┃                    ┃
  ┃                    ┃
  ┃                    ┃
  ┕─battery────────────┛

That is, battery (and switch) and light at opposite corners of a large square, instead of on the middle of a long double-line. Veritasium video implies the current will start flowing at sqrt(2) * width, instead of at 2 * width. Would these effects really work over longer distances like this?

The further the battery and switch get away from the light, the less current you'll see at the battery at (sqrt(2)*width)/c s, since the electric and magnetic fields around the battery and wire will drop in strength as you move further away from them.

Put another way, the main reason this effect is observable in the way shown in the video is because the light and battery, and the wires between them, are so close together. Move them further away, and, per the inverse square law, you'll start seeing a much lower induced current-- the effect may still be there, but it won't be measurable over the noise floor of the experiment setup.

You're right, but sorta. Which is the big problem here, any simplified analogies break down.

What's happening is that you are straying further and further from the "impedance matched" condition (the inductance per unit length stays the same but the capacitance goes up with the separation--however, being "too close" will also cause similar behavior). Consequently, the energy transmitted per reflection gets smaller and smaller.

Part of the problem in this whole discussion is using a "light" as a "threshold detector" where the threshold is effectively microamps. A microamp threshold detector is not what people think of as a "lamp".

If the original Veritasium video had showed the current flow via meter, oscilloscope, etc. nobody would be terribly surprised as it would show small flows getting bigger upon each reflection until it built up to the full current.

This makes more sense and was my first thought watching the video.

Question: At which point does the influence reach actual zero? If it doesn't, does that mean the coffee in front of me is being influenced by Jupiter, however minuscule?

In field theory, IIRC, fields (absent special setups, i.e. in space) are never actual zero, but due to reverse square law they become too small to actually care about quite soon. But the quantum model may have some limitations on that, since stuff can't be arbitrarily small there AFAIK. Not sure what happens about the gravity - likely, Jupiter might influence your coffee, even though in an immeasurably small way, since gravity is very weak. We know the Moon influences our oceans quite prominently. But maybe there are minimums there too?

Yeah, this is what im wondering. The proposed mechanism for this is that the wires generate electric fields that influence electrons remotely. Fine.

What happens when they are not close enough for any meaningful electric field interaction?

He says near the end of the video that a Part 2 video is forthcoming with more exploration of:

- Different sized loops

- Wires closer together / farther apart

- Wires on the ground instead of in air

- Current on both sides of switch

- Wires in two big spread-out loops

- Different strength resistors

The "fast plateau" is pitiful from a power delivery perspective even under tight coupling. Under looser coupling, it becomes proportionately more pitiful.

If they're not connected, then they're just two antennas. What happens when you get far away from your wifi hotspot or a cellphone tower?

The voltage/energy transmitted becomes vanishingly small, and smaller than the thermal noise of the electrons in the other antenna, and undetectable. https://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise

Presumably yes, but it would be very hard to measure since the field falls off with r^2.

Hey, did you make that ascii art by hand or did you use a tool I don't know about? If it's a tool I'd like to use it :)

Just copy pasting from https://en.wikipedia.org/wiki/Box-drawing_character

Nice thank you. TIL

I think the issue with the square would be that the capacitance would be much, much smaller since the wires are separated by a large distance (square law). The capacitance of the original setup is already quite small, but at least it's noticeable on a decent scope. But I doubt you'd see that effect in the square setup.

The other issue with the Veritasium "setup" was that he specified that the wires had no resistance. That being the case the RC time constant would be 0 and thus you wouldn't see that initial charging of the capacitance (and associated current flow) because it would happen instantaneously under those assumptions.

As a parent, Veritasium would be way more preferred teacher to inspire students to search for answer. There are many stellar students who scored A* that later in life just dump what they learnt. You'll be surprised how many medical students didn't make it to MD or not a MD anymore a decade later. Having someone that spurs you to work for it is a weight in gold itself than a great tutor helping you score full understanding and get that A*.

You also need to account for the fact that oscilloscope wires would also be longer going to the light bulb. You can imagine this on the extreme case where light and battery are 1 km apart. Now, you need oscilloscope wires to go 1km far to connect to the light bulb and your timing is off.

The current will always start following after the distance between the switch and bulb divided by the speed of light amount of seconds.

Once the light and battery are far apart, I have a horrible suspicion that the definition of simultaneity will become problematic.

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