Uncertainty Principle Question

[garys_2k]

Has me scratching my head...

We cannot know both an object's velocity and position, I think. But I do know a photon is moving EXACTLY c, so how much does that knowledge make me lose about it's position? IOW, does the UP make photons unbelievably hard to locate? If not, why not? If so, what about all those experiments where the "exact" position of a photon seems to be very exactly determined (i.e., tunneling experiments, two-slit experiment, those sorts)?

Thanks in advance!

 

[Martin]

We cannot know both an object's velocity and position

Momentum and position.

Does that help?

 

[epepke]

We cannot know both an object's velocity and position, I think. But I do know a photon is moving EXACTLY c, so how much does that knowledge make me lose about it's position? IOW, does the UP make photons unbelievably hard to locate? If not, why not? If so, what about all those experiments where the "exact" position of a photon seems to be very exactly determined (i.e., tunneling experiments, two-slit experiment, those sorts)?

Like Martin said, momentum.

And photons are unbelievably hard to locate. The only location you can talk about, really, is where a photon used to exist.

But elsewhere, take photons moving through glass. In transit, their amplitudes are blurred out, every which way, around atoms in several directions at once, and no way to tell which.

In fact, they're so weird and wiggly, some people have thought of them as waves.

But when they hit, it's according to their wavelength, which is entirely in accord with Heisenberg's little principle.

Do the QED. It's much simpler.

 

[cbish]

You have to bombard the particles with different types of light. I don't remember which variable is which but one is measured with low intensity light (down to one photon) and the other with high. So they're inversly proportional. The more accurate you measure one, the more accuracy you lose with the other variable.

 

[Lendri]

garys_2k said

But I do know a photon is moving EXACTLY c

True, but that is it's speed not it's velocity. It's possible to know how fast something is moving but not where it is going

 

[Soapy Sam]

If photons move at c and therefore do not experience time, why would the universe require more than one of them?

 

[BillHoyt]

If photons move at c and therefore do not experience time, why would the universe require more than one of them?

The universe, as a stadium, still experiences time. It also has all these itty-bitty baseball mitts that spend much time trying to catch those speeding photons. If you listen carefully, you can often hear the sound of miniature umps calling "yer out!"