# Few questions on uncertainty principle

• AlbertEinstein
In summary, the two theories, Special Relativity and Quantum Mechanics, are incompatible and cannot be combined. Mass in high velocities is measured using different methods in the two theories.
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?

Thanks

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

AlbertEinstein said:
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.

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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 .

AlbertEinstein said:
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.

oh, can I get dirac eq in QM by resnick

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

AlbertEinstein said:
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.

AlbertEinstein said:
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?

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.

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

## 1. What is the uncertainty principle?

The uncertainty principle is a fundamental concept in quantum mechanics that states it is impossible to know both the exact position and momentum of a particle at the same time. This is due to the wave-particle duality of matter, which means that particles can have both wave-like and particle-like properties.

## 2. Who discovered the uncertainty principle?

The uncertainty principle was first proposed by German physicist Werner Heisenberg in 1927. Heisenberg's work on the uncertainty principle was a crucial step in the development of quantum mechanics and earned him a Nobel Prize in Physics in 1932.

## 3. How does the uncertainty principle affect our understanding of the physical world?

The uncertainty principle has significant implications for our understanding of the physical world. It means that the behavior of particles at the subatomic level is inherently uncertain and unpredictable. This challenges our traditional understanding of cause and effect and suggests that the universe may be fundamentally probabilistic rather than deterministic.

## 4. Can the uncertainty principle be overcome?

No, the uncertainty principle is a fundamental principle in quantum mechanics and cannot be overcome. It is a natural limitation to our ability to observe and measure the behavior of particles at the subatomic level.

## 5. How is the uncertainty principle used in practical applications?

The uncertainty principle is used in various practical applications, including laser technology, computer memory, and medical imaging. It is also essential in the development of quantum technologies, such as quantum computing and quantum cryptography.

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