How do relativity and quantum mechanics contradict each other?

In summary, the conversation discusses the issue of reconciling quantum mechanics (QM) and relativity. The Schrodinger equation, which is the fundamental equation of QM, is not lorentz-invariant, meaning it gives different results for observers in relative motion. Additionally, QM always maintains a conserved particle number, which conflicts with the idea of particle creation in relativity. The Dirac equation attempts to reconcile the two theories, but it is still missing some features and is not fully relativistic. It is also noted that massive particles can never reach the speed of light.
  • #1
mrspeedybob
869
65
I didn't think this question really belonged in either sub-section so I put it here. I hope that's OK. I've always heard that they contradict each other but I've never understood how. What predictions do they make differently?
 
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  • #2
The biggest issue is that the Schrodinger equation (the fundamental equation of QM) is not lorentz-invariant. This means that the equations of QM are different for two observers moving at a relative velocity to one another---which is clearly unacceptable for relativity.

Additionally, QM always maintains a conserved particle number. From relativity we learn that [tex]E=\gamma mc^2[/tex], and thus whenever the energy of a system (e.g. a pair of photons) is greater than the rest mass energy of another particle-pair (e.g. electron-positron pair), we can expect some probability of particle creation.
 
  • #4
some one told me yesterday that massive particles indeed can reach the speed of light, is this true?
 
  • #5
snackster17 said:
some one told me yesterday that massive particles indeed can reach the speed of light, is this true?

99.99...% the speed of light and as many "9"'s you can afford, but never 100% the speed of light.

Now frankly, it does make sense that anything massive could never go as fast as something that is not.
 
  • #6
Dr Lots-o'watts said:
What about the Dirac equation? What is it missing to reconcile the two?
http://en.wikipedia.org/wiki/Dirac_equation
I'm pretty sure the dirac equation is fully relativistic.

The Dirac equation is still missing other features... e.g. remember it only applies to spin-1/2 particles, and its still not a field theory---so again, it has issues with varying particle number.
 

1. What is the difference between relativity and quantum mechanics?

Relativity and quantum mechanics are two separate theories that attempt to explain different aspects of the physical world. Relativity, specifically the theory of general relativity proposed by Albert Einstein, describes the behavior of large objects and their relationship to gravity. On the other hand, quantum mechanics describes the behavior of subatomic particles and their interactions.

2. How do relativity and quantum mechanics contradict each other?

The main contradiction between relativity and quantum mechanics is that they have different understandings of the fundamental nature of reality. Relativity suggests that space and time are continuous and deterministic, while quantum mechanics suggests that they are discrete and probabilistic. Additionally, relativity does not account for the behavior of subatomic particles, while quantum mechanics does not account for the effects of gravity on a large scale.

3. Can relativity and quantum mechanics be unified?

Many scientists and researchers have attempted to unify relativity and quantum mechanics into a single theory, known as quantum gravity. However, as of now, there is no widely accepted theory that successfully combines these two theories. The search for a unified theory is still ongoing and is considered one of the biggest challenges in modern physics.

4. How do experiments support the contradictions between relativity and quantum mechanics?

Many experiments have been conducted that seem to support both relativity and quantum mechanics separately, but not together. For example, the famous double-slit experiment demonstrates the wave-particle duality of subatomic particles, which is a fundamental concept in quantum mechanics. However, this experiment cannot be explained by the laws of relativity. Similarly, the gravitational lensing effect, which is a prediction of relativity, cannot be explained by quantum mechanics.

5. How do scientists reconcile the contradictions between relativity and quantum mechanics?

As mentioned earlier, the search for a unified theory that reconciles the contradictions between relativity and quantum mechanics is ongoing. Some scientists propose that there may be an underlying theory that encompasses both theories, while others suggest that our understanding of the universe may need to change drastically in order to reconcile the contradictions. Ultimately, the reconciliation of these two theories remains a mystery and is an active area of research in the scientific community.

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