Slashdot Mirror
Physicists Confirm a Pear-Shaped Nucleus, and It Could Ruin Time Travel Forever (sciencealert.com)
An anonymous reader writes from a report via ScienceAlert: Physicists have confirmed the existence of pear-shaped nuclei, which challenges the fundamental theories of physics that explain our Universe. "We've found these nuclei literally point towards a direction in space. This relates to a direction in time, providing there's a well-defined direction in time and we will always travel from past to present," Marcus Scheck from the University of the West of Scotland told Kenneth MacDonald at BBC News. Until recently, it was generally accepted that nuclei of atoms could only be one of three shapes: spherical, discus, or rugby ball. The first discovery of a pear-shaped nucleus was back in 2013, when physicists at CERN discovered isotope Radium-224. Now, that find has been confirmed by a second study, which shows that the nucleus of the isotope Barium-144 is also asymmetrical and pear-shaped. In regard to time travel, Scheck says that this uneven distribution of mass and charge caused Barium-144's nucleus to "point" in a certain direction in spacetime, and this bias could explain why time seems to only want to go from past to present, and not backwards, even if the laws of physics don't care which way it goes.
Nice thought but no, there is no center as you're thinking, space itself expanded with the big bang so the big bang happened literally everywhere. At least as far as we know.
How do we know time doesn't go backward? Maybe it does. We'd never know it if it did. (think about it.)
Surprising as it seems we would actually know if time reversed because of what seems to be one of the most forgotten results of particle physics: the laws of physics do not work the same if time is reversed due to something called "T-violation": literally time-reversal symmetry violation. This is NOT the same thing as a glass falling off a table will not reassemble itself and flying back onto the same because this is an effect of entropy.
The first evidence for T-violation came from the CP-LEAR kaon experiment at CERN in 1998 [Phys. Lett. B 444 43 (1998)] and was confirmed in B-decays by Babar in 2012 (and as evidence that this result is always forgotten they forgot about the CP-LEAR measurement in this article!!). These experiments looked at how a particle oscillates back and forth between two possible states. What they found is that a particle in state A will oscillate into state B faster than one in state B will oscillate into state A. Hence the process prefers to go in one direction more than the other even though in this case the two states have identical entropy.
So if time were reversed you would be able to detect it by doing the same experiment and finding that now the particles would go from B to A faster than from A to B. Incidentally this symmetry is also closely related by special relativity to the symmetry between matter and anti-matter so reversing time would switch our universe into one which prefers anti-matter over matter and we could detect this flip again with particle physics experiments.
So amazing as it seems we could detect a flip in the direction of time and the article is just plain wrong when it says that the laws of physics don't care which way time goes: they do and we have evidence to show it!
Time only "goes from" the past to the future because we define those terms by the way that time "goes", and time "goes" the way it does, from less-entropic to more-entropic states
Actually that is not true because of something called T-violation which has been observed in kaon and B-meson oscillations (see my other reply to a post below for details but this is NOT an effect of entropy!).
What the hell could pear-shaped nuclei possible have to do with any of that?
This is harder to explain and you are absolutely correct that the article utterly fails to do so! We have three special symmetries in particle physics called C, P and T where T is time-reversal and C and P together, CP, is the symmetry between matter and anti-matter. What relativity tells us is that all three together, CPT, should be a perfect symmetry of nature. This means that CP (the matter-antimatter symmetry) and T (time reversal) are linked because if the T symmetry is violated then the CP symmetry must be violated in exactly the opposite way so that CPT altogether is conserved.
Now the pear shaped nucleus is interesting because the nucleus is bound together by the strong force and every test so far suggests that the strong force obeys C, P and T separately (and so of course also CPT together). The weird violation of T and CP is only seen in the weak force (which causes nuclear beta decay). Now if a nucleus has a non-symmetric shape it suggests that the strong force also violates P, called parity. If P is conserved then if you flip the direction of the x, y and z axes there is no change. However with a pear-shaped nucleus there would be a change and so parity is said to be violated and this means that CP would also be broken.
So, if true, this result would be interesting because we have never seen this effect in the strong force despite it being possible to add a term to do this and it has always been a mystery as to why this term appeared to be exactly zero - it is called the "strong CP problem". Since CP is tied to CPT by relativity this means that we would expect time reversal to be broken as well by the strong force. However despite the BBC's best effort to advertize Dr. Who this result says absolutely nothing about whether time travel is possible just that time seems to have a preferred direction...which we have known since 1998 thanks to the CP-LEAR experiment.
As for the "pointing in the same direction in space" I want to see that written in a journal before I give it any credence. Given there are several errors and mistakes elsewhere in the article I the journalism behind this story is seems appalling and I think they completely misunderstood the explanation given...which as you can see above is not exactly trivial!