Quantum Physics

Thank you Halfwise ^^ it's nice to get another perspective on things, like it said but on other words, than just from the book I think i get the whole picture a bit better now ^^


ofc.. high school

i thought that was only in the movies

is that a picture




Or a table

Good one !

I now feel my live has been wasted on occupations that will never be recorded on youtube. Hence forgettable.

Hello Halfy!

Petty has drawn me into a discussion on the Dr Who thread, and we're needing a non-martian intro to causuality in physics.

When you've got time, could you give us a quick summery of cause and effect in Newtonian, relativistic, and quantum physics, please? (You do those things so much better than I... )

This is an animated gif of some slow motion footage of a golf bottle hitting off a surface. As you can see, it completely loses its shape, as if it's some sort of rubber. Something that you wouldn't expect to happen.

Thats impressive

I'm not sure that's a true golf ball! I think it IS made of rubber.

David H wrote:Hello Halfy!

Petty has drawn me into a discussion on the Dr Who thread, and we're needing a non-martian intro to causuality in physics.

When you've got time, could you give us a quick summery of cause and effect in Newtonian, relativistic, and quantum physics, please? (You do those things so much better than I... )

Drat, missed it. Looked back at the Who thread, not sure I really have anything pertinent to contribute. Einstein won't let a wave of causality travel faster than light, Galileo will. If I ever get around to writing the relativistic clock thing I can get into Einstein's time travel thing, but he only allows you to travel forward, not backward.

That's OK. I've successfully resisted that line of argument for now. I still think it's something several people in Forumshire would enjoy though.

The role of the observer is something that's not always intuitive, and the Einstein time travel thought problems are a great way to get your head around the basic vocabulary of causality.

Once that's been covered, I know that sometime Petty would love to wrestle with quantum entanglement and the paradoxes of quantum pairs.
But I know my limits. I'll never write that one!

I am all for the discusions and the mind bending! Any time you can muster the theories Halfy! (Just give me warning so I can get the extra buckies in)

Was reading a story on the BBC- a small bit of pace debris put a bullet sized hole through the space station solar panels.

And there was -

If the piece of debris were to collide with the hull, the space station's shielding would probably protect the crew from being adversely impacted.

Shielding? Are we talking thick plating here or something more ST?

#1 Google result for "space station shielding"

http://usatoday30.usatoday.com/tech/science/space/2007-05-30-iss-spacewalk_N.htm

Seems that ray/particle shields are still a ways off.

I'm guessing they're referring to the radiation/heat shielding. Think more like insulation.

protect the crew from being adversely impacted.

That's a nice bit of governmental language! Adversely impacted...yeah I guess that is what happens when you're hit by high speed bullet-sized objects.

maybe its just me becoming less funny but everyone seems really funny at the moment


keep it up guys!

David H wrote:That's OK. I've successfully resisted that line of argument for now. I still think it's something several people in Forumshire would enjoy though.

The role of the observer is something that's not always intuitive, and the Einstein time travel thought problems are a great way to get your head around the basic vocabulary of causality.

Once that's been covered, I know that sometime Petty would love to wrestle with quantum entanglement and the paradoxes of quantum pairs.
But I know my limits. I'll never write that one!

Did I never get into quantum entanglement? I guess I didn't. That's okay because the implications are more logical than real, at least the spooky stuff is. You still can't transmit information faster than light, or you can, but it doesn't matter because you don't know what the information is until you see it, which doesn't affect nuttin' 'cause you can't travel faster than light....ah hell. May as well do a simple example right here, right now.

Okay, let's say an electron and positron collide. They instantly make mincemeat of each other, and all that's left is a couple of photons. Why two photons? because a single photon with that much energy has to be going in some direction, carrying momentum with it in that direction. What if the original electron and positron had momenta that cancelled out? Then what? One high energy photon can't possibly have zero momentum, but two photons can go in different directions and cancel out. So there has to be more than one photon in order to handle all the possibilities.

Ahem. So you've perhaps got two photons going in different directions. You can capture each one by holding up a glass ball that's silvered inside, and once the photon's inside you close up the hole and the poor thing goes bouncing around inside like a trapped minnow. You capture both of them. These are light traps.

Now the thing is, the two photons have to conserve some quantities: the total energy has to add up to equal the total energy of the initial electron and positron, as does the momentum and angular momentum. This experiment usually deals with angular momentum but more people are familiar with energy so we'll use that.

So two people are carting each of the two photons around in different traps. Since you haven't measured the photons, you don't know how much energy each one has, but you know if you measure one, the other one must have exactly the missing amount of energy. The thing is, if you do the quantum math it will not tell which photon has which energy (actually it would from the vector math if you know which way it came out of the collision, but assume we don't have that). So as soon as you measure the energy of one photon, you instantly know the energy of the other. It doesn't matter how far away it is, the knowledge is there.

Some people say this is an example of information travelling faster than light, but that's a hunk of malarky because knowing the energy of the photon at that distance doesn't let you DO anything with that information, because it's too far away. If you wanted to place a bet that you know what the energy of the photon is based on a measurement clear on the other side of the universe, well, you can. But you have to wait for the guy on the other side of the universe to tell you what the energy of the first photon was.

So the whole spookiness comes down to the mathematics of quantum mechanics telling you there's a 50% probability of one photon having less than half the energy, but once you check it the other photon has a 100% probability of having the remaining energy. Big whoop. You can twist yourself into logical knots over this, but why bother?

Where does Amy come into it again?

Amy was the name of Schrodinger's cat.

halfwise wrote: Big whoop. You can twist yourself into logical knots over this, but why bother?

Why bother, he asks!

Why bother going to all the trouble of colliding an electron and a positron, then carefully collecting the photons if your not going to twist yourself into logical knots, I'd like to know!