B Can Time Truly Flow Backwards in Quantum Physics and Cosmology?

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The discussion centers on the nature of time as described by physicists like Sean Carroll and Carlo Rovelli, particularly the idea that the laws of physics do not inherently dictate a direction for time. It is argued that while macroscopic events appear to have a clear forward direction, fundamental physical laws allow for time to be reversed without contradiction. The concept of entropy is highlighted, suggesting that the increase in entropy gives the illusion of a forward flow of time, but this is not a fundamental requirement of the universe. The conversation emphasizes the distinction between theoretical reversibility in physics and the irreversible nature of everyday experiences. Ultimately, the complexity of time's direction and its relationship to physical laws remains a challenging topic for many to grasp.
  • #51
vanhees71 said:
The only velocity that is restricted to be is the signal velocity, i.e., the velocity with which the wave front propagates.
Hi vanhees:

I again reference Wikipedia.
In 1994 Nimtz and Horst Aichmann [3] carried out a tunneling experiment at the laboratories of Hewlett-Packard after which Nimtz stated [3] that the frequency modulated (FM) carrier wave transported a signal 4.7 times faster than light due to the effect of quantum tunneling.​

I think I must be misinterpreting the meaning of your quote at the top of this post, as well as what I underlined in the Wikipedia quote. Both seems to be saying that the information carried in the signal/message is traveling faster than c. However, since the speed of transmission of information is limited by relativity to be no greater than c, the quotes must mean the signal/message may travel faster than c, but the information carried by the signal does not. This would make sense only if we understand that part of the signal must get lost or distortred during the transmission. Is this correct?

Regards,
Buzz
 
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  • #52
It's not you who is misinterpreting anything but Nimtz. Evanescent modes in wave guides (that's what "tunneling" means) are no exception to the "relativistic speed limit". Also there the front velocity is ##c## (at least within the standard electromagnetic theory of wave guides). It also hasn't anything to do with any quantum effect. Of course the math of tunneling in quantum theory is completely analogous to the tunneling of classical electromagnetic waves, but the meaning of a classical wave is very different from the wave function in non-relativistic quantum mechanics. I'm a bit puzzled by the somewhat biased Wikipedia entry on this subject.
 
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