Few questions on uncertainty principle

[AlbertEinstein]

Can we mix SR and uncertainty principle? for ex. from uncertainty principle we have \Delta x \Delta p \geq h/4\pi.
Books then write m \Delta x \Delta v \geq h/4\pi with an assumption that m can be measured accurately.
However form SR we know that mass depends on velocity; with mass increasing with velocity. Now if we can't measure v exactly how can we measure m exactly?

please explain.
Thanks

 

[AlbertEinstein]

Hey guys. please help. Have I written something silly.? pls explain. I hope this is not homework type question.

 

[DaveC426913]

Can we mix SR and uncertainty principle?

You have just tripped over what is arguably the greatest problem in 20th century physics.

SR and QM are both theories that have been tested with exquisite precision, two of the best tested theories in the history of science, and they passed with flying colours. SR beautifully describes the macroscopic world - gravity, stars, galaxies and the universe. QM beautifully describes the subatomic world - atoms, electrons, quarks.

Yet they cannot be combined. Putting the two together generates infinities. They are incompatible as we currently understand them. Our understanding of the universe is broken.

 

[AlbertEinstein]

Then what should I assume:write the eq quantum way or non-quantum way? If both are incompatible then how masses at high velocties are measured? btw I heard that only GR is not compatible .

 

[selfAdjoint]

Then what should I assume:write the eq quantum way or non-quantum way? If both are incompatible then how masses at high velocties are measured? btw I heard that only GR is not compatible .

Albert, the relativity problem DaveC was talking about was the general covariance of General Relativity. For Special Relativity there are good unifications with Quantum. Dirac's equation for the electron is one, and all the accepted Quantum Field Thoeries from QED to the Standard Model are "manifestly covariant" in the SR sense of the term. If you just want to do electrons, look up Dirac, it's usually in the first or second chapter of any QFT textbook.

 

[AlbertEinstein]

oh, can I get dirac eq in QM by resnick

 

[DaveC426913]

My bad. I was talking about GR and QM, not SR and QM.

 

[jtbell]

oh, can I get dirac eq in QM by resnick

If you mean, "can I find the Dirac equation in Resnick's QM book", try looking in the index.

 

[Los Bobos]

However form SR we know that mass depends on velocity; with mass increasing with velocity. Now if we can't measure v exactly how can we measure m exactly?

please explain.
Thanks

It is actually more consistent to say, that from SR we know that mass does not increase with velocity. Here you would have to think what is momentum in SR. And of course the biggest problem of elementary QM, the difference in the handling of spatial and temporal coordinates.

 

[jtbell]

The postings discussing mass in relativity, which used to be located here, are now in the following thread in the relativity forum:

https://www.physicsforums.com/showthread.php?t=144545

Please make further postings along this line in that thread. Discussion about the uncertainty principle can continue in this thread here. Thanks in advance for your cooperation.