h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

You say they are carried out in parallel universes, but might i ask how it come back to our universe if it was in a parallel universe that it was done in? i know i might of missed the answer that but im quite tired.


I love the way that a particle can be in two places or posses two states unless it is seen. that just is funny, it makes it look shy or somthing, how does it know we are looking?

Your first question was how the particles come back to this universe once the calculations have been done. As far as I know, nobody knows the answer to that. However, in String Theory, particles like the photon and electron can move/vibrate in 10 or 26 dimensions (!) and therefore, I assume that they can move out of this universe to a higher dimension, and enter a parallel universe. They could easily come back afterwards.

However, the accepted reason for the moment is that the particles don't actually go to the parallel universes - they only have a certain probability of being there, represented by their wave function (determined by Schroedinger's equation).

Your second question was how the particles know we are looking at them. Here's my best answer:

Particles do appear to be very shy. In addition to changing states when observed, sub-atomic particles also have the ability to quantum tunnel. Suppose you enclosed a barrier around a sub-atomic particle. As you do this, the particle gets worried and starts vibrating. Then, when you enclose the barrier tightly enough, the particle just goes straight through the barrier as if it's claustrophobic.

The reason? The best thing I can think of is the String Theory bit again. You see, particles exist in more than one place simultaneously because their alternative position is in a parallel universe. It's the wave function again. I presume the way that they quantum tunnel is by jumping into a higher dimension.

now could you answer me this. Why does hardly anybody enjoy quantum phyiscs? its so amazing

because to quote a famous physicist, if you are not unsettled by quantum theory, you haven't understood it.

it takes a certain kind of person to like being involved in a subject which fundamentally knocks your beliefs every time you ask it an awkward question.

That's a good question. If you told someone that you were interested in quantum physics they would probably think you were mad and say 'it's all beyond me'. If you told someone that it's possible for sub-atomic particles to exist in mutliple places at once then they'd probably think you were mad and possibly quite drunk.

There is another reason, of course. How much quantum physics do we learn at school? There's nothing about quantum physics in the Comprehensive National Curriculum. Neither is there much about it in A-Level physics, apparently. This is a shame. The universe is as much quantum as it is classical, and the government thinks it can get away with teaching us only half of the way the universe works. It's disheartening.

So perhaps because of its madness, the government doesn't want to teach it. And because it isn't taught, people don't believe it. Shame.