= 27d567bc2d48d9f40e9ccc20ea370b15)
RolfAndreassen comments on Quantum Physics, CERN and Hawking radiation - Less Wrong
You are viewing a comment permalink. View the original post to see all comments and the full post content.
= 783df68a0f980790206b9ea87794c5b6)
Loading…= b715d02e85f7b3b4ae65ca3d3e450868)
Subscribe to RSS Feed
Powered by Reddit
= f037147d6e6c911a85753b9abdedda8d)
You are viewing a comment permalink. View the original post to see all comments and the full post content.
Comments (66)
If so, then how can T symmetry hold? You seem to be saying that T symmetry implies CPT symmetry. But we know from experiment that CP symmetry is broken. If T symmetry holds, and CP symmetry does not hold, then CPT symmetry cannot hold.
Really, this looks pretty straightforward. The theory you quote has A->B. Experiment !B. Consequently, either !A or !(A->B).
Why do you think so?
Particle momenta, no; spin, yes. Although spin is angular momentum, it does not come about because particles are rotating about an internal axis, as you seem to have in mind. (To the best of anyone's knowledge, of course.) Consequently parity does not auto-reverse under time-reversal.
OK - so, you don't understand the idea. There is a much more detailed description of the associated model written by someone else here.
The punchline at the bottom reads:
Please let me know if that fails to sort you out - and you are still interested.
First, the theory rests on the airy assertion that reversing T automatically causes the reversal of spin and other quantum numbers as well. I found the argument given for this unconvincing. Second, and more importantly, you do not seem to have grasped that you cannot possibly have both T symmetry and CPT symmetry, because CP symmetry is experimentally excluded. It does not matter if you invent a special form of T symmetry that is 'equivalent' to CPT symmetry.
Take a physical system that exhibits CP violation; assume it is described by the kind of theory outlined in your link. Now reverse time. By the argument in your link, this also reverses CP. Because the system is not symmetric under CP, it exhibits different behaviour. Bing, T symmetry has been broken: There is a measurement I can make that tells me which way time is flowing.
Well, I don't have a watertight argument for the first point. I think it is more likely than not, but if your intuition is the other way around, I won't argue too much. What I object to is the idea that T-symmetry is wrong. In fact, T-symmetry is pretty plausible, IMO.
From your second point, (from my perspective) you still don't get the logic of the whole idea - and you have exhausted most of my resources on the subject, so I am not sure what more to do with you.
Assuming that charge and parity quanta involve moving parts internally, then they would both reverse automatically if time is reversed - producing what appears to be CPT symmetry as a result. That would be consistent with all known experiments, and physics would then by time symmetric.
You said: "Because the system is not symmetric under CP, it exhibits different behaviour." No, because you have also reversed time, (you just said so yourself) - and if C,P and T are all reversed, then symmetry is restored. So, then there is no measurement you can make that tells you which way time is flowing.
No. Start with a left-handed neutrino. Reverse T under your assumption. It is now a right-handed antineutrino going the other way; reverse space as well to restore the original direction, if you like, although the argument does not depend on this. Because CP is broken, right-handed antineutrinos do not behave exactly as left-handed neutrinos do. Therefore you can tell how many times T has been reversed. You don't get the full symmetry back except by applying CP another time.
Yes.
A parity flip, I presume you mean.
That is indeed true.
Well you only said you reversed it once - and then you flipped P, but not C, leaving things in a bit of a mess - and then you tried to make out the mess was something to do with me.
Reversing T an odd number of times changes everything. Reversing it an even number of times changes nothing. You can't distinguish between reversing T different numbers of times beyond that - under the hypothesis that reversing T automatically reverses C and P.
Ok, leave the parity flip out of it. If this is true:
then you do not have T symmetry. Done.
It makes time run backwards. Those in charge may not think that this is such a null-op.
If you pressed the "rewind" button, you would normally expect to see some changes!
Ok, there's your problem: You don't understand what is meant by 'symmetry'.
At this stage, I don't really see why you are continuing to comment :-(