Causality in quantum mechanics and relativity

In summary, the uncertainty principle states that certain events such as double slit and decay of an atom has no causal history, hence a violation of causality, uncaused events. However, relativity states faster than light travel violates causality. So if the two events are quantum, A and B, then there causality would not apply? Only if the event is superluminous.
  • #1
ensabah6
695
0
According to Heisenberg uncertainty principle, certain events such as double slit and decay of an atom has no causal history, hence a violation of causality, uncaused events.
But relativity states faster than light travel violates causality.

Since quantum mechanics does not respect causality, why should sending information faster than c do so?
 
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  • #2
In these two cases the word "causality" is used in different contexts and has different meanings.

When in QM we say that atomic decay is not causal we mean that there is no identifiable physical reason for the atom to decay at this particular moment.

In SR we are dealing with two classical events A and B, such that A is definitely a cause of B. The causality postulate demands that A happens earlier than B in all reference frames. If information travels superluminally from A to B, then one can find a reference frame in which the effect (B) occurs earlier than the cause (A). This violates the causality postulate.

Eugene.
 
  • #3
meopemuk said:
In these two cases the word "causality" is used in different contexts and has different meanings.

When in QM we say that atomic decay is not causal we mean that there is no identifiable physical reason for the atom to decay at this particular moment.

In SR we are dealing with two classical events A and B, such that A is definitely a cause of B. The causality postulate demands that A happens earlier than B in all reference frames. If information travels superluminally from A to B, then one can find a reference frame in which the effect (B) occurs earlier than the cause (A). This violates the causality postulate.

Eugene.

So if the two events are quantum, A and B, then there causality would not apply?
 
  • #4
Only if the event is superluminous. It is the act of exceeding light speed where time becomes skewed. Thus if A causes B.. B could happen before A.
 
  • #5
ensabah6 said:
So if the two events are quantum, A and B, then there causality would not apply?

The issue is the word "causality". It means different things to different people.

In QM, things do not happen for known reasons. They instead follow laws of chance. Those statistical laws are very useful. But they do not - at this time - allow for one to say definitely that "cause A leads to effect B". So QM is considered acausal. Some do not accept this, but the experimental results appear to support it. There is no actual evidence that there is any direct cause to the outcome of a quantum event.

An example would be radioactive decay. Or actually, any decay event.
 
  • #6
DrChinese said:
The issue is the word "causality". It means different things to different people.

In QM, things do not happen for known reasons. They instead follow laws of chance. Those statistical laws are very useful. But they do not - at this time - allow for one to say definitely that "cause A leads to effect B". So QM is considered acausal. Some do not accept this, but the experimental results appear to support it. There is no actual evidence that there is any direct cause to the outcome of a quantum event.

An example would be radioactive decay. Or actually, any decay event.

Oh my mistake. I didn't even address the contextual difference.

This corresponds to the random production and destruction of photons as well right?
 
  • #7
DrChinese said:
So QM is considered acausal. Some do not accept this, but the experimental results appear to support it. There is no actual evidence that there is any direct cause to the outcome of a quantum event.

DrChinese, (I have wanted to ask you about this once. :smile:)

Can you say the experimental results such as the fine structure(like one between 2P1/2 and 2P3/2) also support the "probabilistic" acausal idea?
You are probably talking about the acausal Schroedinger equation (S.E.) which shows the probability density.
But the "probabilistic" S.E. can't explain the relativistic effects (including the spin-orbital interactions).
So it is "incomplete".

On the other hand, the Dirac equation (D.E.) which satisfies the (relativistic) causality can explain this relativistic effects.
Of course, D.E. is not "probabilistic".(= D.E. doesn't show the probability density.)

As shown in this site, As the atoms become heavier (which means the atomic nucleus charge becomes larger), the experimental results become more different from that of S.E., because the electon's speed becomes faster.
In S.E., irrespective of the nucleus charge, the electrons of any atoms are all static as electron clouds obeying the probability density, aren't they?

[To be precise, in D.E., only one of plus or minus energy solutions is not causal. And if we use the Coulomb force, it is not causal. But as an approximation, D.E. is superior to S.E.]

I think QM always contains the "vague" parts like this (which will continue forever, as long as QM continue).
Over 80 years have passed since the QM appeared.
But the discussions like the "interpretation" continue even now.
(Here, I'm not talking about the interpretation of QM, but talking about the "inconsistency" between the relativistic and nonrelativistic QM.)

In QM, the relativistic QM is superior to the nonrelativistic QM in the experimental results.
But, are you saying "acausal" QM is superior ?
Of course, "Photons" which satisfy the Maxwell's equation are "relativistic" particles, too.
 
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  • #8
lol.

80 years is a blink of the eye in any science.
 

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

In quantum mechanics, causality is interpreted as probabilistic, meaning that events can only be predicted with a certain probability. In relativity, causality is based on the principle of causality, which states that the cause of an event must always precede its effect in time. This means that in relativity, events are determined by their past conditions, while in quantum mechanics, there is an inherent uncertainty in predicting events.

2. Can causality be violated in quantum mechanics?

According to the Copenhagen interpretation of quantum mechanics, causality cannot be violated because the act of measuring an event in quantum mechanics affects its outcome. However, some interpretations of quantum mechanics, such as the Many-Worlds interpretation, suggest that causality may be violated in certain situations.

3. How does relativity affect causality?

In relativity, the concept of causality is closely tied to the speed of light being the maximum speed at which information can travel. This means that events that are not causally connected, or cannot affect each other due to distance, cannot occur at the same time. This can lead to the concept of time dilation, where the passage of time is relative to the observer's reference frame.

4. Can causality in quantum mechanics and relativity be reconciled?

There is ongoing research and debate on how to reconcile the seemingly contradictory concepts of causality in quantum mechanics and relativity. Some theories, such as quantum gravity, aim to unite these two theories and explain how causality works on a larger scale. Others argue that causality is a fundamental concept that cannot be fully understood in the context of these theories.

5. Is causality a fundamental law of nature?

The concept of causality is a fundamental part of our understanding of the world, but whether it is a law of nature itself is still a topic of debate. Some theories, such as determinism, suggest that causality is a fundamental law that governs the universe, while others, such as indeterminism, argue that causality is a human construct and does not necessarily apply to all phenomena.

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