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Comment by dogma1138 | Hacker News Reader

Electrons have mass they can't move at the speed of light. Photons also have other nice properties such as wavelength which open a whole suit of possibilities e.g. like having a logic gate which can operate in different mods based on the wavelength and polarization of the light.

While this is technically possible with electronics as well by setting a different voltage limit it's much more effective with photonic computing and doesn't not increase the complexity of your base components as much.

The current designs for a photonic computer are also much more parallel most of them basically layers of LED's and detectors with a very fast LCD matrix which serves as a mask between them. if you have a 256x256 pixel screen you can perform an operation on 65536 bits in a single clock, if you stack them up you basically getting 1 order of magnitude with each layer this isn't something you could ever achieve with current solid state electronics.

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Information we move around using electrons moves much faster than any single electron - because electrostatic field changes move at speed of light obviously, so the electrons at the end of wire start moving as soon as the electrostatic field change gets to it.

You don't have to wait with processing for the electron from the beggining of the wire to get to the end?

So, the difference between photons and electrons speed as measured by the time it takes electronic and optical signal to move through the same distance - is insignificant.

I didn't say that we need to move electrons (although we do for some things like Flash Memory), but you are confusing simple wave propagation in conductors with electron mobility in semiconductors which is quite a bit more complicated.

You also need to remember that when we talking about waves then the wavelength ties directly to your data throughput, and with electrons the wavelength in conductors at say a frequency of 1GHZ is still around 3 kilometers, visible light has much much shorter wavelengths which allows you to pass more data per given amount of time.

Yeah I was thinking about conductors, didn't realized it's different in semiconductor.

Regarding the wavelength - it's another of these things I never quite understood about physics. I've been told that every particle can be thought of as a wave with a frequency, and that it corresponds to the energy of the particle. Photons have lower energies than electrons or protons, so the wavelength of electrons should be shorter, not longer?

You've mixed and matched some of the stuff, leave wave-matter duality aside. You can treat it as any other wave in that regards best analogy will be acoustic waves because they are very simple. http://farside.ph.utexas.edu/teaching/em/lectures/node102.ht...

What fraction of the speed of light are electrons moving at in the most advanced silicon chip we have? Trying to understand how much speed is left on the table for us to pick up in serial processing?

It's not that easy to define because were talking about semi-conductors after all;)

They don't move at a constant speed like say in a conductor (which isn't the case either because electric field causes resistance e.g. eddy currents, but lets say a super-conductor)

You have quite a few concepts with semiconductors primarily saturation velocity (which in most cases is the peak velocity, but not necessarily attained in actual operation) which is also affected by the drift velocity due to any electric fields in your components.

https://en.wikipedia.org/wiki/Saturation_velocity

Light speed in vacuum is 29979245800 cm/s Saturation velocity in Si based SC is 10000000 cm/s

So there's quite a bit of difference there ;)

So does this imply an opportunity to improve computing speed by 2997?

No because the speed of the components with the current designs is still limited by the switching speed of the masking matrix. And in any case you will still need to transform photons back to electrons twice. The speed of electrons or EM wave propagation vs photons isn't a player in why photonic computing might be better. The ability to encode more data into the photons, a much more power efficient and inherently parallel design are.

Also because light has much more shorter wavelength than "electricity" electromagnetic waves in conductors (kilometers vs nano-meters) you can have a much higher throughput with light even if you use it to replace the carrier wires in electronics (which is what Intel is working on they want to keep electronic switching but make all carriers photonic).

https://en.wikipedia.org/wiki/Speed_of_electricity

Light moves 3*10^8 m/s in a vaccuum, which is 7.5cm per clock cycle of a 4GHz processor. The processor is about 2cm wide, so not much room for improvement I figure.

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