5 ms·

Was just wondering the same. I suspect the Planck Length is a lower bound on the hypothetically smallest unit of distance, however in practice perhaps it's larg

Was just wondering the same. I suspect the Planck Length is a lower bound on the hypothetically smallest unit of distance, however in practice perhaps it's larger. The difference between this experimental resolution (10^-18m) and the Planck Length (10^-35m) is absolutely enormous though, so a negative result would still be very inconclusive and highly likely.

Retra 9y ago
If there's a smallest unit of distance, shouldn't there be a shortest wavelength? And thus a smallest difference in wavelength and maximum energy? And a smallest energy change? And thus there must be a minimally different relative velocity, to preserve discretization of relativistic energies and momenta? And a thousand other things we also have no evidence for?
- lnanek2 9y ago
  > And a smallest energy change? > And a thousand other things we also have no evidence for? It's called quantum physics because it was proven that there is a small amount of energy which is basically the indivisible unit of energy. So yes, that exists, and has been proven. It is the whole point of quantum physics, quantum referring to an amount and the smallest packet being a "quanta of light": https://en.wikipedia.org/wiki/Quantum https://en.wikipedia.org/wiki/Quantum
  - ars 9y ago
    > that there is a small amount of energy which is basically the indivisible unit of energy What? No. Quantum physics means that things happen in "bundles", usually small ones. But it does not define any particular size to those bundles. They could be big, they could be small. > "quanta of light": https://en.wikipedia.org/wiki/Quantum https://en.wikipedia.org/wiki/Quantum You misunderstand your link. A quantum is the smallest unit of energy in that particular interaction. In other interactions the quantum could have a different magnitude.
  - deleted 9y ago
    [deleted]
- ars 9y ago
  > If there's a smallest unit of distance, shouldn't there be a shortest wavelength? If I remember correctly a photon with a wavelength of the plank length would become a black hole. > And a smallest energy change? No, small energy is large wavelength. Not all energy must be representable by wavelength anyway - imagine an energy difference so slight the equivalent photon has a wavelength greater than the size of the universe. > And thus there must be a minimally different relative velocity No, as per above. > momenta Angular momentum is quantized, so study that and it might help. > And a thousand other things we also have no evidence for? We can still theorize. PS. To whoever downmodded him: Only downmod offtopic and stupid. Questions, even those with an anti-authoritative tone should not be downmodded, but rather answered.
  - SomeStupidPoint 9y ago
    Is there any reason there can't be a photo with a wavelength greater than the width of the (visible) universe? It seems like a photon with a 96 billion lightyear wavelength has 2 * 10^-52 Joules of energy. (1 * 10^-33 eV); is there any reason a photon can't have that little energy?
    - ars 9y ago
      Among other things it would take 96 billion years to create the photon. So that means whatever process created it needs to take that long. I'm not sure what would happen if the process is interrupted before it's complete. But I suspect the photon would "go back in time", and never have been emitted in the first place. This "time travel" doesn't pose issues because the photon takes that long to be detected, so if it's interrupted it simply wouldn't be detected. See also: https://en.wikipedia.org/wiki/Soft_photon https://en.wikipedia.org/wiki/Soft_photon
      - SomeStupidPoint 9y ago
        Wouldn't it only take 13 billion years if you'd started at the big bang and a photon that had the wavelength of the then observable universe (since space stretched under it)? I also have to ask how that jives with it being a quantized change: either the photon emits or it doesn't (since a photon exists with that energy or it doesn't) -- or there's some probability distribution that we'll detect the photon (which might change over time) -- but how can it be half emitted 46 billion years in the process? In the end, either it provides a kick at its energy level to another property (eg, electron momentum) in one quantum jump.

Retra 9y ago

If there's a smallest unit of distance, shouldn't there be a shortest wavelength? And thus a smallest difference in wavelength and maximum energy? And a smallest energy change? And thus there must be a minimally different relative velocity, to preserve discretization of relativistic energies and momenta? And a thousand other things we also have no evidence for?

lnanek2 9y ago
> And a smallest energy change? > And a thousand other things we also have no evidence for? It's called quantum physics because it was proven that there is a small amount of energy which is basically the indivisible unit of energy. So yes, that exists, and has been proven. It is the whole point of quantum physics, quantum referring to an amount and the smallest packet being a "quanta of light": https://en.wikipedia.org/wiki/Quantum https://en.wikipedia.org/wiki/Quantum
- ars 9y ago
  > that there is a small amount of energy which is basically the indivisible unit of energy What? No. Quantum physics means that things happen in "bundles", usually small ones. But it does not define any particular size to those bundles. They could be big, they could be small. > "quanta of light": https://en.wikipedia.org/wiki/Quantum https://en.wikipedia.org/wiki/Quantum You misunderstand your link. A quantum is the smallest unit of energy in that particular interaction. In other interactions the quantum could have a different magnitude.
- deleted 9y ago
  [deleted]
ars 9y ago
> If there's a smallest unit of distance, shouldn't there be a shortest wavelength? If I remember correctly a photon with a wavelength of the plank length would become a black hole. > And a smallest energy change? No, small energy is large wavelength. Not all energy must be representable by wavelength anyway - imagine an energy difference so slight the equivalent photon has a wavelength greater than the size of the universe. > And thus there must be a minimally different relative velocity No, as per above. > momenta Angular momentum is quantized, so study that and it might help. > And a thousand other things we also have no evidence for? We can still theorize. PS. To whoever downmodded him: Only downmod offtopic and stupid. Questions, even those with an anti-authoritative tone should not be downmodded, but rather answered.
- SomeStupidPoint 9y ago
  Is there any reason there can't be a photo with a wavelength greater than the width of the (visible) universe? It seems like a photon with a 96 billion lightyear wavelength has 2 * 10^-52 Joules of energy. (1 * 10^-33 eV); is there any reason a photon can't have that little energy?
  - ars 9y ago
    Among other things it would take 96 billion years to create the photon. So that means whatever process created it needs to take that long. I'm not sure what would happen if the process is interrupted before it's complete. But I suspect the photon would "go back in time", and never have been emitted in the first place. This "time travel" doesn't pose issues because the photon takes that long to be detected, so if it's interrupted it simply wouldn't be detected. See also: https://en.wikipedia.org/wiki/Soft_photon https://en.wikipedia.org/wiki/Soft_photon
    - SomeStupidPoint 9y ago
      Wouldn't it only take 13 billion years if you'd started at the big bang and a photon that had the wavelength of the then observable universe (since space stretched under it)? I also have to ask how that jives with it being a quantized change: either the photon emits or it doesn't (since a photon exists with that energy or it doesn't) -- or there's some probability distribution that we'll detect the photon (which might change over time) -- but how can it be half emitted 46 billion years in the process? In the end, either it provides a kick at its energy level to another property (eg, electron momentum) in one quantum jump.