# The Naked Scientists Forum

### Author Topic: Fully in two places at the same time?  (Read 6794 times)

#### cover it

• First timers
• Posts: 2
##### Re: Fully in two places at the same time?
« Reply #25 on: 31/12/2011 18:45:36 »
If you stand in front of a mirror, theoretically you are now in two places at one time  ;D

#### David Cooper

• Neilep Level Member
• Posts: 1505
##### Re: Fully in two places at the same time?
« Reply #26 on: 31/12/2011 20:02:47 »
I think I might be getting somewhere. Please tell me where I've gone wrong with this:-

You start out with an electron positron pair in a spin singlet quantum state, then you move them far apart before examining them. You want to examine them both at the same time, so I imagine that means repeating the experiment many times with different delays between both measurements to cover the possibility that the whole experiment is moving relative to a possible preferred frame of reference. No matter how you do the experiment you always find that you can only successfully measure the x-spin of both particles or the z-spin of both particles, but you can never measure the x-spin of one and the z-spin of the other without finding one or other of them to be uncertain.

Now, I must have got part of that wrong, because if you manage to measure the x-spin of one particle and fail to get a certain answer when trying to measure the z-spin of the other, that would indicate that the former measurement really did occur before the latter, and that would allow you to identify a preferred frame of reference by pinning down simultaneous events separated in space.

#### imatfaal

• Neilep Level Member
• Posts: 2787
• rouge moderator
##### Re: Fully in two places at the same time?
« Reply #27 on: 04/01/2012 11:11:03 »
Quote from: JP
From a mathematics standpoint, a point with no extension is easy to imagine

Mathematically, I agree; but then I try to apply this to the "real" world and say something like: if I put 100 of these points side by side, would they still occupy no space, because 0 x 100 = 0.

Possibly so - but in reality various forces mean that a point particle can have a range of influence - ie stop you putting them "side by side".

On a more philosophical note - if the maths and the theory works, then why does it matter that we puny humans cannot get our head around a concept.  QM, GR, and Particle Physics are strange stuff - and all require an acceptance that not everything is readily (or even possibly) visualisable (is this a word - my spell-check says no).  The nub of the matter is that modern science is the creation of models that accurately predict experimental/observational outcomes - not about some inner hidden truth.  Even a Grand Unified Theory would be really just be set of equations and conditions that allowed precise predictions to be made - and not a description of an final truth.

#### The Naked Scientists Forum

##### Re: Fully in two places at the same time?
« Reply #27 on: 04/01/2012 11:11:03 »