5 ms·

> the speed of light is a bottleneck for processors It's not the speed of light [in a vacuum], but electric signal propagation speed in copper.

• SpaceRaccoon 6y ago
  And the "electric signal" is an electromagnetic wave- also known as light. Nowhere did they imply the speed of light in a vacuum, the speed of light in copper is an equally valid interpretation.
  • mhh__ 6y ago
    That's true but it's easy to forget that the velocity factor of that wave is significantly smaller in (say) copper than air or a vacuum.
    • SpaceRaccoon 6y ago
      The velocity factor of light in glass is also significantly smaller, about 70%.
  • adwn 6y ago
    > And the "electric signal" is an electromagnetic wave- also known as light. No, it's not. If it were, you'd have photons moving through your copper wire, which would be quite the sensation! A moving electron does create a change in the electromagnetic field, however, so maybe that's where your confusion stems from?
    • ben_w 6y ago
      More charitably, charge carriers do move much more slowly than the electric field they transmit[0], and while you’re correct that the time-varying electric field in a processor is not light (nor even a radio wave), if the chips were much larger or much higher frequency the chips and buses would risk becoming antennas and having all the problems that would bring — 5 Ghz ~= 6cm wavelength [1] ~= 3cm half-wave dipole. [0] https://en.m.wikipedia.org/wiki/Speed_of_electricity https://en.m.wikipedia.org/wiki/Speed_of_electricity [1] http://www.wolframalpha.com/input/?i=c%2F5ghz http://www.wolframalpha.com/input/?i=c%2F5ghz Edit: if the chips were much larger. Smaller chips can go faster without becoming antennae.
• Gravityloss 6y ago
  An electric signal in a wire can't travel faster than the speed of light.
  • adwn 6y ago
    > An electric signal in a wire can't travel faster than the speed of light. So? That means that the speed of light is an upper bound, but it's not a bottle neck.
    • Gravityloss 6y ago
      An electrical signal travels close to the speed of light (not the electrons). Even when of course no light travels inside the copper. If something oscillates at 1 GHz, 15 cm down the wire the phase is opposite. To me it's perfectly correct to say that speed of light affects the design a lot and in many places probably is a bottleneck.
  • StavrosK 6y ago
    Neither can my car.
    • Gravityloss 6y ago
      Your car does not travel even close to the speed of light for it to matter. But electrical signals do.
• Koshkin 6y ago
  The velocity of signal propagation in copper is close to that of light. (Not to be confused with the mean velocity of the electrons.)