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Particle Physicists Confirm Arrow of Time Using B Meson Measurements

Unknown Lamer posted about 2 years ago | from the one-way-trip dept.

Science 259

ananyo writes with bad news for John Titor. From the article: "Four years after its closure, researchers working with data from the Stanford Linear Accelerator Center's particle physics experiment BaBar have used the data to make the first direct measurement confirming that time does not run the same forwards as backwards — at least for the B mesons that the experiment produced during its heyday. The application of quantum mechanics to fundamental particles rests on a symmetry known as CPT, for charge-parity-time, which states that fundamental processes remain unchanged when particles are replaced by their antimatter counterparts (C), left and right are reversed (P), and time runs in the reverse direction (T). Violations of C and P alone were first seen in radioactive decays in the 1950s, and BaBar was used to confirm violations of CP in B meson decays in 2001. To keep CPT intact, that implies that time reversal is also violated, but finding ways to compare processes running forward and backward in time has proven tricky. Theoretical physicists at the Universityof Valencia in Spain worked with researchers on BaBar to exploit the fact that the experiment had generated entangled quantum states of the meson Bzero and its antimatter counterpart Bzero-bar, which then evolved through several different decay chains. By comparing the rates of decay in chains in which one type of decay happened before another, with others in which the order was reversed, the researchers were able to compare processes that were effectively time reversed version of each other. They report in Physical Review Letters today that they see a violation of time reversal at an extremely high level of statistical significance."

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Arrow of Time... (5, Funny)

Anonymous Coward | about 2 years ago | (#42033793)

Arrow of Time confirmed... Wheel of Time fans disappointed.

Re:Arrow of Time... (3, Insightful)

Anonymous Coward | about 2 years ago | (#42033885)

Thus is our treaty written; thus is agreement made.
Thought is the arrow of time; memory never fades.
What was asked is given; the price is paid.

Re:Arrow of Time... (-1)

Anonymous Coward | about 2 years ago | (#42034143)

Gay faggot spotted. Go choke on a dick, fag boy.

Re:Arrow of Time... (3, Funny)

haruchai (17472) | about 2 years ago | (#42034813)

Really? A gay faggot? Is that anything like a straight heterosexual or just a very ecstatic bundle of twigs?

Re:Arrow of Time... (0)

girlintraining (1395911) | about 2 years ago | (#42034407)

Arrow of Time confirmed... Wheel of Time fans disappointed.

I've been disappointed since I realized the books were very engaging, exceptionally self-consistent, and... not only sexist but was a central component of the story. That sorta ruined it for me.
-- A sad panda geek girl.

Re:Arrow of Time... (3, Funny)

Nyder (754090) | about 2 years ago | (#42034765)

Arrow of Time confirmed... Wheel of Time fans disappointed.

I've been disappointed since I realized the books were very engaging, exceptionally self-consistent, and... not only sexist but was a central component of the story. That sorta ruined it for me.
-- A sad panda geek girl.

yep, I noticed the women in the story were very mean to men...

Re:Arrow of Time... (2)

socceroos (1374367) | about 2 years ago | (#42035431)

Sexist? C'mon, seriously? Women were construed in a particular light were they? But, so were men? Granted, Robert had some funny views and an odd angle to things, but both sexes were firmly put in boxes. No need to get your knickers in a knot.

Re:Arrow of Time... (1, Flamebait)

girlintraining (1395911) | about 2 years ago | (#42036229)

, but both sexes were firmly put in boxes.

That, sir, is the definition of sexism.

Re:Arrow of Time... (0, Funny)

Anonymous Coward | about 2 years ago | (#42036305)

Oh... don't you worry your pretty little head...

Re:Arrow of Time... (1, Insightful)

socceroos (1374367) | about 2 years ago | (#42036461)

No, not quite - stereotyping/generalising is an element of sexism in many cases, but not the definition of it. I don't find, in any way, that the books elevate one sex over the other as more valuable.

Re:Arrow of Time... (5, Insightful)

fredprado (2569351) | about 2 years ago | (#42036555)

Hardly. Recognizing that there are differences between the sexes is common sense. Judging people's values and defining their roles solely by their sexes is sexism.

Women and men are not equal in everything. Trying to see equality in everything because it fits your notion of symmetry, fairness or whatever is self-delusion.

Re:Arrow of Time... (0)

smitty_one_each (243267) | about 2 years ago | (#42034499)

Oh, many a shaft at random sent [random.org]
Finds mark the archer little meant!
And many a word at random spoken
May soothe, or wound, a heart that's broken!
—Sir Walter Scott, Lord of the Isles

CPLEAR (4, Insightful)

Roger W Moore (538166) | about 2 years ago | (#42035477)

Arrow of Time confirmed... Wheel of Time fans disappointed.

Physicists on the CPLEAR experiment will be disappointed as well - they actually discovered this effect (called T-violation) back in the 1990's before Babar was running by looking at kaon oscillations produced in low energy proton/antiproton collisions [Phys. Lett. B 444 43 (1998)]. So Babar was certainly not the first experiment to see the "arrow of time" although it is the first to do so using B mesons.

Reading the Article Backwards... (2, Funny)

Anonymous Coward | about 2 years ago | (#42033829)

Well, reading the article backwards still results in WTF?

Re:Reading the Article Backwards... (0)

Anonymous Coward | about 2 years ago | (#42034149)

The person posting it didn't understand it, and therefore couldn't summarize it. Hence, its length.

Re:Reading the Article Backwards... (2)

marcosdumay (620877) | about 2 years ago | (#42034169)

Whan read backwards it sounds like a foreign language and I can't understand a word. Thus, no change in that.

Now, seriously, the paper's abstract makes more sense than the article. And it is heavy in a jargon that I don't completely understand, while the article was arguably translated into normal english. What a bad translation!

Re:Reading the Article Backwards... (4, Funny)

avgjoe62 (558860) | about 2 years ago | (#42034495)

Funny - I read the article backward and I got that Paul is dead.

Re:Reading the Article Backwards... (4, Informative)

History's Coming To (1059484) | about 2 years ago | (#42036059)

Here's my take on it:

In theory the basic mathematics of quantum theory is time-symmetric. You can write equations to describe particles x and y colliding to produce a and b, and those equations work perfectly well to describe particles a and b colliding to produce x and y. It's why Feynman diagrams are so useful, you can just flip the time dimension around and see something else described by the same maths.

The point of what these folks have done is to look very closely at one particular Feynman diagram, that of the B meson decay, and showing that it is not time symmetric in some way. So the flow of time is something extra on top of the basic quantum theory...that's fascinating.

I Wish (4, Funny)

NEDHead (1651195) | about 2 years ago | (#42033833)

They would be more specific about the arrow of time. I get that they have confirmed it and all, but which direction is it pointing?

Re:I Wish (0)

Anonymous Coward | about 2 years ago | (#42033883)

It's pointing along the time axis. Matter progress in one direction along the time axis and apparently antimatter progresses in the opposite direction.

Re:I Wish (1)

fsck1nhippies (2642761) | about 2 years ago | (#42033895)

Even better... How do you turn it around. I wanna win that bet on the world series.

Re:I Wish (1, Funny)

Mitchell314 (1576581) | about 2 years ago | (#42033931)

Slightly to the left, until I see the doctor again.

Re:I Wish (3, Funny)

Black Parrot (19622) | about 2 years ago | (#42035931)

which direction is it pointing?

Slightly to the left, until I see the doctor again.

Oh, great. Now time has a liberal bias too.

Re:I Wish (4, Informative)

girlintraining (1395911) | about 2 years ago | (#42033995)

They would be more specific about the arrow of time. I get that they have confirmed it and all, but which direction is it pointing?

As I understand it (greatly simplified), time is a consequence of matter and energy interactions in space; They don't all happen at once though because of separation, and the distance (relative or absolute) between them is what creates time. That's why they call it 'spacetime'; The smallest unit of time then is the fastest change in quantum state possible. As time is a byproduct of matter and energy interactions, and couldn't exist without it, there's still the question of the "arrow of time". We perceive it to be always moving "forward", but there's no reason why the reaction A-B-C shouldn't go C-B-A as well, or instead.

If I understand this experiment correctly, what they're saying is "as well" is bogus. It's not just that it isn't observable, but that it just doesn't happen. No matter which way the reaction chain goes, there's no mirror reaction that goes unobservable. But perhaps someone who actually is a particle physicist could provide a layman explanation better than mine... I'll be honest: Most of what they do is beyond my grasp because they talk mostly in math and seem to eschew visualization or story explanation. -_-

Re:I Wish (4, Interesting)

TexVex (669445) | about 2 years ago | (#42034227)

The arrow of time is the reason why random bits of shrapnel and chemicals don't fly together and "un-detonate" to become hand grenades. In one direction of time, entropy in the universe always increases; in the other, it always decreases. The question is, why? If everything at the quantum level always worked the same way forwards as it does backwards, then entropy would be constant; the universe would be in some kind of steady state and nothing would matter because we wouldn't be here.

I think at this stage of research, it's more about finding clues than it is about trying to put them together into a coherent explanation. But if that's not true, I'd love to hear from someone who really knows this stuff..

Re:I Wish (2)

girlintraining (1395911) | about 2 years ago | (#42034755)

The question is, why? If everything at the quantum level always worked the same way forwards as it does backwards, then entropy would be constant; the universe would be in some kind of steady state and nothing would matter because we wouldn't be here.

Maybe the universe was bored with the idea... :\

Re:I Wish (0)

Anonymous Coward | about 2 years ago | (#42036465)

Going against the forward bias hard enough to let the magic smoke out of the subspace quantum diodes sounds like it might be really really bad. Most people tend to like the universe (because that's where we keep all our stuff), so let's not break it by trying too hard.

Re:I Wish (2, Interesting)

Anonymous Coward | about 2 years ago | (#42035137)

I don't really know this stuff that well. I did well in quantum computing, which covers the philosophy of the quantum postulates, but never really gets past baby level physics. That said, I've been thinking that maybe there's a bit more to flip than C, P, and T to get a better picture.

If you think of an explosion starting at time 0 and centered at [0,0,0], you start with density concentrated around that point and over time it spreads out from that point. Alternatively, starting at time t and going backwards to time 0, you see the dispersed mass flowing to concentrate at that point.

However, another picture is that starting at time 0, a lack of matter begins flowing into the area around the point [0,0,0]. Essentially this view looks at it like the negative space in a painting.

These two pictures aren't quite mirror images of each other, however with a coordinate transformation it might be possible to make them mirror images of each other. Something along the lines of mapping [0,0,0] to the point at infinity and continuously map the points surrounding the origin such that [1/d,1/d,1/d] goes to [d,d,d], basically turning space inside out around your origin point.

Re:I Wish (5, Informative)

FrangoAssado (561740) | about 2 years ago | (#42035287)

If everything at the quantum level always worked the same way forwards as it does backwards, then entropy would be constant; the universe would be in some kind of steady state and nothing would matter because we wouldn't be here.

That's not true. "Everything at the quantum level always working the same way forwards and backwards" is completely consistent with the second law of thermodynamics ("entropy never decreases"), and completely consistent with the observable universe (barring CP violation). All that's necessary is that the universe started with very low entropy -- like, say, the Big Bang.

See for example this from this Arrow of Time FAQ [preposterousuniverse.com] (from cosmologist Sean Carroll):

The observed macroscopic irreversibility is not a consequence of the fundamental laws of physics, it's a consequence of the particular configuration in which the universe finds itself. In particular, the unusual low-entropy conditions in the very early universe, near the Big Bang. Understanding the arrow of time is a matter of understanding the origin of the universe.

Re:I Wish (2, Informative)

msevior (145103) | about 2 years ago | (#42035301)

The arrow of time is the reason why random bits of shrapnel and chemicals don't fly together and "un-detonate" to become hand grenades. In one direction of time, entropy in the universe always increases; in the other, it always decreases. The question is, why?

The reason is very simple. Entropy is a measure of the probability of a particular outcome. The statement that "entropy increases" is simply the statement that the most probable thing to do happen is almost always the one that does happen. The "almost always" is a fantastically high probability. For example if I through a 1 cm cube of of aluminium at 26 C into a lake where the water is at a temperature of 25 C, there is something like a 10 ^-(10 ^10^23) chance that heat will from the lake into the aluminium cube and cause it's temperature to rise. If it did this the entropy of the Universe would decrease.

What this experiment observed is profound and extremely interesting. For some reason that isn't known, the Universe prefers that certain microscopic and reversible processes occur with a greater probability if time increases.

In other words there truly is a preferred direction to time which independent of tautology that the Universe is constantly evolving into a more probable state.

Actually this result is was first observed in K-mesons but this new result in B-mesons has much greater significance and confirms the previous observation.

Entropy vs. T-symmetry (4, Informative)

Roger W Moore (538166) | about 2 years ago | (#42035419)

The arrow of time is the reason why random bits of shrapnel and chemicals don't fly together and "un-detonate" to become hand grenades.

No, that is entropy. The reason that balls fall off tables and rarely bounce onto them (when provided with enough heat energy) is because there are many, many more states where the balls atoms vibrate incoherently and only one state (or a tiny handful) where the vibrations are organized enough to cause it to bounce back onto the table.

With mesons you can study a particle oscillating between two states. What you find is that the P(A -> B) is not equal to the P(B -> A) where B is the anti-particle state of A and there is no entropy involved. It's all to do with something called CPT symmetry which is a result of relativity and, since CP together are violated (anti-matter is not exactly the same as matter) we expect that T (time reversal symmetry) is also violated so this is an expected result.

Re:I Wish (4, Informative)

ceoyoyo (59147) | about 2 years ago | (#42035563)

The arrow of time refers to the fact that we perceive a difference between the past and the future: we remember the past, but not the future. That's explained adequately by noting that entropy tends to increase and the universe, for some reason, was in a low entropy state in the past.

What they've found is that, at least for b-mesons, going forward in time is different than going backward in time, presumably in addition to the rest of the universe accumulating entropy. It's as if there was a fundamental difference between moving "north" and moving "south" in empty space.

Re:I Wish (-1)

Anonymous Coward | about 2 years ago | (#42034081)

It's pointing at me.

I took an arrow of time to the knee.

Re:I Wish (2)

Anubis IV (1279820) | about 2 years ago | (#42034157)

Left if you're facing one way, but right if you're facing it from the other side. If you're facing it head-on or are behind it, you're holding your time wrong.

Re:I Wish (0)

Anonymous Coward | about 2 years ago | (#42034381)

It's pointing to infinity and beyond

Re:I Wish (5, Interesting)

Anonymous Coward | about 2 years ago | (#42035067)

Take a video of some physical process and run it in reverse. At a macro level we humans can generally tell that the video is in reverse - tea cups break apart when hitting a floor, they don't spontaneously assemble and then fly off the floor. However, if you analyze such situations using the physics you learned in high school, there is no way to tell that the course of events has been reversed - statistically it's very unlikely that a tea cup would do that, but there is nothing physically impossible about it. So it appear that the laws of physics are the same if time was running in reverse yet to us humans it does not appear that things would be the same if time was running in reverse - because of entropy.

This is the problem of the arrow of time - how can we tell in a physical way which way time is running? Is there any way to distinguish going forward in time to going backward in time using just physical laws? You could say that entropy increases with time (the basis of how we humans can tell on a video whether it is running forward or backward), but that is only a statistical observation and it only holds because it just happens to be that our past has a very small amount of entropy compared to the high entropy situation that the universe will eventually reach. Increasing entropy is a consequence of an accident of what our past looks like and it is not a physical law in the strict sense we are looking for here. So entropy is not a good candidate. This research shows a way that you actually CAN tell if time is running in reverse. Though physicists still believe that there is a CPT symmetry, indicating that if you reverse time and also two other things, then there is no way to tell from physical laws that you did that.

Re:I Wish (1)

evil crash (739354) | about 2 years ago | (#42035487)

In the Northern Hemisphere time moves from left to right, in the Southern, it's right to left.

Can't go back to first! (-1)

Anonymous Coward | about 2 years ago | (#42033853)

^H

Time (3, Funny)

oodaloop (1229816) | about 2 years ago | (#42033863)

Time flies like an arrow. Fruit flies like a banana.

That's all I've got to contribute. Carry on.

Re:Time (0)

Anonymous Coward | about 2 years ago | (#42034033)

But bananas are boomerang shaped, so I guess we might all be in for a big "havent we been here before?" moment...

Re:Time (0)

Anonymous Coward | about 2 years ago | (#42034417)

It's deja vu all over again.

Re:Time (1)

rossdee (243626) | about 2 years ago | (#42034579)

Boomerangs have an airfoil shape in cross section, bananas are just circular in cross section. its the lift generated by the airfoil shape, and gyroscopic forces that cause a boomerang to come back. I wonder how many millenea it took for the aborigines to refine that

The question remains - what does Newsweek fly like?

Re:Time (0)

Anonymous Coward | about 2 years ago | (#42034055)

I thought fruit flies like beer.

Re:Time (1)

InfiniteBlaze (2564509) | about 2 years ago | (#42034105)

Time flies like an arrow. Fruit flies like a banana. That's all I've got to contribute. Carry on.

Fruit flies poorly without wings or an outside force acting upon it.

Re:Time (1)

AwesomeMcgee (2437070) | about 2 years ago | (#42034153)

Are you insulting bananas!?

Re:Time (1)

statusbar (314703) | about 2 years ago | (#42034233)

No he is insulting fruit flies.

Re:Time (2)

sconeu (64226) | about 2 years ago | (#42034411)

No, but if someone attacks you with a banana, you'd better have a pointed stick ready.

Also, this "BaBar" experiment seems rather elephantine to me.

Re:Time (2)

Sexy Commando (612371) | about 2 years ago | (#42034811)

Yes. That was a banana...No one expects the banana!

Re:Time (0)

Anonymous Coward | about 2 years ago | (#42034577)

Is there a "-1 anti-comedy" mod.

Re:Time (1)

Longjmp (632577) | about 2 years ago | (#42034743)

Time flies like an arrow. Fruit flies like a banana.

Wow. I didn't know Groucho Marx was also a particle physicist ;)

Re:Time (0)

Anonymous Coward | about 2 years ago | (#42035517)

It took me years to figure out the intended parsing of that sentence...

Re:Time (1)

dudpixel (1429789) | about 2 years ago | (#42035627)

Fruit flies like a banana.

Yes. Yes they do :)

Yes ... (1)

Kaz Kylheku (1484) | about 2 years ago | (#42033933)

Time does not run the same way backward as it does forward. It, like, runs forward and does not run backward.

Re:Yes ... (1)

AwesomeMcgee (2437070) | about 2 years ago | (#42034265)

It's much more careful going backwards, it walks instead of running, good thing too, wouldn't want time to trip and fall.

Re:Yes ... (2)

Mateorabi (108522) | about 2 years ago | (#42036011)

Actually, it's more like a big blob of wibbley wobbley, timey wimey.... stuff.

Inverted Truth (0)

KlomDark (6370) | about 2 years ago | (#42033957)

This is all a giant mix of hogwash and bullshit intended to discredit (amongst only the easily-impressed, low-information scientists of the validity of Doctor Emmett Brown's proven research.

Re:Inverted Truth (0, Insightful)

Anonymous Coward | about 2 years ago | (#42034193)

There is an unmatched parenthesis in your comment. Somehow I think the missing parenthesis is necessary to help people parse the sentence correctly.

Re:Inverted Truth (1)

Anonymous Coward | about 2 years ago | (#42034327)

) time travel. (Please ignore everything between the parenthesis, thank you)

Re:Inverted Truth (1)

Ultra64 (318705) | about 2 years ago | (#42035129)

"(Please ignore everything between the parenthesis, thank you)"

Um

Re:Inverted Truth (1)

reboot246 (623534) | about 2 years ago | (#42036033)

It's very hard to write something inside of a parenthesis. The plural of 'parenthesis' is 'parentheses'.

wait what? (1)

Trunksword (2585203) | about 2 years ago | (#42034021)

After reading the whole thing, I still don't understand a thing it said. Maybe I'm illiterate.

Re:wait what? (5, Informative)

Baloroth (2370816) | about 2 years ago | (#42034785)

Let me explain. Most reactions are time-reversible. (Sort of) example: oxygen and hydrogen can combine to form water and release energy, but you can put energy back into the system to get hydrogen and oxygen back out again (thermodynamics states you will always lose some energy in this process, however, no matter how efficiently you conduct the H+O->water->H+O process).which indicates time is not perfectly reversible, but doesn't explain why). At the subatomic level, however, some similar (vaguely similar, anyways) reactions cannot be reversed, or don't reverse in the same way. In this case, they studied a meson that spontaneously changes from matter to antimatter and back (don't ask). If time reversibility held true for them, the probability of matter->antimatter would be the same as the probability of antimatter-> matter. It was not, by a very very very very significant margin (14 sigma, or a 1 in 10^43 chance this was seen by accident). Note this may also help to explain why matter is more prevalent than anti-matter in our universe.

Re:wait what? (0)

mcneely.mike (927221) | about 2 years ago | (#42035505)

Bazinga! :)

Re:wait what? (0)

Anonymous Coward | about 2 years ago | (#42035905)

THANK YOU for your easy to understand explanation.

Re:wait what? (2)

Black Parrot (19622) | about 2 years ago | (#42035949)

But what does it all *mean*?

Should I buy a Tesla, or give everything I own to the poor and go stand on the mountaintop?

Damn it, where is my car analogy! (1)

Derekloffin (741455) | about 2 years ago | (#42034029)

I'm totally lost. So they tracked the decay of particle in the past by having them entangled with with particles from the future? Sorry, my feeble little brain has obviously reached its limit.

Re:Damn it, where is my car analogy! (1)

Kergan (780543) | about 2 years ago | (#42034093)

Same. I hope some quantum physicist will chime to mention how one can observe time going "backwards" and how this extremely high level of statistical significance isn't another way of saying that they can't.

Re:Damn it, where is my car analogy! (1)

edxwelch (600979) | about 2 years ago | (#42034351)

Ok: A Ford Fiesta made entirely of anti matter would travel backwards in time and turn left when you wanted to go right.

Re:Damn it, where is my car analogy! (1)

ceoyoyo (59147) | about 2 years ago | (#42035609)

No, they watched particles "decaying" in one way versus ones "decaying" in the opposite direction. The second process would be identical to the first if you were running time backwards.

Re:Damn it, where is my car analogy! (1)

Black Parrot (19622) | about 2 years ago | (#42035961)

This is Slashdot. You're supposed to demand a flying car analogy.

Dear Slashdot: (4, Insightful)

Anonymous Coward | about 2 years ago | (#42034095)

Bet you wish you had unicode now, eh?

Re:Dear Slashdot: (0)

Anonymous Coward | about 2 years ago | (#42035785)

Too bad the TFA used the same moronic typesetting, not a /. issue.

noy really the arrow of time (3, Interesting)

bcrowell (177657) | about 2 years ago | (#42034103)

I wouldn't really describe this as confirming the arrow of time.

The really powerful arrow of time is the thermodynamic one. The second law of thermodynamics says that entropy always increases. This thermodynamic arrow is essentially the same arrow as the psychological one, which allows us to remember the past but not the future, and all the other ones we see in nature, such as the laws of black hole thermodynamics, which say that the area of a black hole's event horizon always grows with time. This group of time-arrows, which are all essentially the same time-arrow, appear to occur because the big bang was fine-tuned to be extremely low in entropy, with its gravitational-wave degrees of freedom inactive. Nobody knows why we had a low-entropy big bang, when a random choice of initial conditions would be overwhelmingly more likely to produce a maximum-entropy one. (In particular, inflation doesn't explain it. Also, statistical mechanics doesn't explain it, because to produce the second law from statistical mechanics, you need to assume a low-entropy initial state.)

This paper is about an arrow of time that is obscure and completely unrelated to the others. It has to do with the weak nuclear force. Unlike the others, it has essentially no effect on the world we see around us.

Re:noy really the arrow of time (1)

inputdev (1252080) | about 2 years ago | (#42034549)

I wouldn't really describe this as confirming the arrow of time.

The really powerful arrow of time is the thermodynamic one. The second law of thermodynamics says that entropy always increases. This thermodynamic arrow is essentially the same arrow as the psychological one, which allows us to remember the past but not the future, and all the other ones we see in nature, such as the laws of black hole thermodynamics, which say that the area of a black hole's event horizon always grows with time. This group of time-arrows, which are all essentially the same time-arrow, appear to occur because the big bang was fine-tuned to be extremely low in entropy, with its gravitational-wave degrees of freedom inactive. Nobody knows why we had a low-entropy big bang, when a random choice of initial conditions would be overwhelmingly more likely to produce a maximum-entropy one. (In particular, inflation doesn't explain it. Also, statistical mechanics doesn't explain it, because to produce the second law from statistical mechanics, you need to assume a low-entropy initial state.)

Would cooling from expansion and corresponding symmetry breaking explain it? Why would the big bang have to be a low-entropy state in any global sense (and what difference would that even make?), wouldn't entropy still be able to increase from any initial point?

This paper is about an arrow of time that is obscure and completely unrelated to the others. It has to do with the weak nuclear force. Unlike the others, it has essentially no effect on the world we see around us.

Is it possible that this observation is related to an increase of entropy that is not properly described by the particles in the model?

Re:noy really the arrow of time (0)

Anonymous Coward | about 2 years ago | (#42035155)

That things started at low entropy is an accident of facts about the infinitesimal (compared to infinity) amount of time at the very beginning of our universe. In terms of the infinite time that the universe will exist, it will immediately reach a high entropy state and the arrow of time that you are referring to will cease to be relevant. Yet this finding will persist. Although, since they still believe that the CPT symmetry exists, this isn't actually an arrow of time at all - there still appears to be no arrow of time in physics at all, as I understand it, apart from this quaint situation we are in that will immediately cease to be the case on the universe's time scale.

Re:noy really the arrow of time (1)

shoor (33382) | about 2 years ago | (#42035269)

Nobody knows why we had a low-entropy big bang, when a random choice of initial conditions would be overwhelmingly more likely to produce a maximum-entropy one

The explanation that I see is that there might be a 'multiverse', many big bangs, most of which would not produce a universe that could support life. Therefore, we're here because this is the one in a skadzillion that could and did produce life intelligent enough to wonder about this stuff. It's a plausible explanation to me, but that doesn't mean it's correct of course.

I'm still looking for a really good explanation of what the article is about. The 'arrow of time' I'm familiar with, and which has been mentioned in other posts, is the entropic one. There are so many ways for things to get disarrayed as opposed to the extremely few for them to get re-arrayed, that we never see it happen, nevert see things like objects getting hotter than ambient temperature without a source of heat or things randomly assembling themselves into some recognizable order.

Re:noy really the arrow of time (0)

Anonymous Coward | about 2 years ago | (#42035281)

We don't currently have an explanation of entropy. We have a lot of observation, but no good sound reason for it.

Re:noy really the arrow of time (1)

ceoyoyo (59147) | about 2 years ago | (#42035623)

"it has essentially no effect on the world we see around us."

Well, except for being necessary for CP violation, which in turn is the only way we have of explaining why there isn't much antimatter around.

So it does explain why the planet is here and doesn't experience nuclear-style detonations many times an hour as antimatter grains of dust hit the atmosphere. But other than that no effect on the world around us.

Four years? (1)

DaveyJJ (1198633) | about 2 years ago | (#42034107)

Well that took enough time, didn't it.

Re:Four years? (1)

AwesomeMcgee (2437070) | about 2 years ago | (#42034181)

They just needed a significant enough sample size for their time experiment to be proved out, like four years.

Re:Four years? (1)

Nidi62 (1525137) | about 2 years ago | (#42034329)

It actually took 6 years, but since they kept turning back time it really only took 4.

Explanation? (0)

Anonymous Coward | about 2 years ago | (#42034163)

Could some kind particle physicist out there please provide an explanation of this and why it is important.

Can I have the time back (1)

ozduo (2043408) | about 2 years ago | (#42034281)

That I spent reading this!

Re:Can I have the time back (1)

oldhack (1037484) | about 2 years ago | (#42035865)

No. You know why? Cuz time don't go back.

Yes... (-1)

Anonymous Coward | about 2 years ago | (#42034395)

but will it blend?

arXiv link (5, Informative)

Baron Eekman (713784) | about 2 years ago | (#42034447)

Come on people, how hard is it to include the arXiv link? Just google the title, it's usually the first hit.
http://arxiv.org/abs/1207.5832 [arxiv.org]

WRT: The Arrow of Time... (0)

VortexCortex (1117377) | about 2 years ago | (#42034677)

Confusyah say: Time flies like an arrow, but fruit flies like a banana.

What this means (5, Informative)

SoftwareArtist (1472499) | about 2 years ago | (#42034773)

The summary is a bit confusing if you don't know what it's talking about. The title is even worse, since it implies the exact opposite of what it actually means. Let me try to explain it.

First: physicists believe that the "arrow of time" isn't a fundamental property of the laws of nature. There's no fundamental difference between "forward in time" and "backward in time". The laws of physics operate identically in both directions. So why do those directions seem so different? Why do objects fall down but not up? Why can you make an egg into an omelet, but not an omelet back into an egg? Why can you remember the past, but not the future? This turns out to be a property of our local region of spacetime. More precisely, we live very close (a mere 13.5 billion years or so) away from a point of incredibly low entropy (known as "the big bang"), and that creates an entropy gradient throughout our region of spacetime. What we call "forward in time" simply means "the direction of increasing entropy", or more simply, "away from the big bang".

A good analogy (not involving a car - sorry!) is the direction "down". It seems obvious to you that one particular direction in space is fundamentally different from all other directions. Objects fall down. They don't fall in any other direction. Yet to person on the other side of the earth, the direction they call "down" is completely different from the direction you call "down". That's because the "arrow of gravity" is not a fundamental property of the laws of nature, just a property of our local region of space. "Down" means "toward the center of the earth." In the same way, "forward in time" means "away from the big bang".

Second: what I just said swept a few details under the rug. You see, the true symmetry is not time reversal (which would imply that simply reversing the direction of time would leave all laws of physics unchanged), but a slightly more complicated symmetry called CPT invariance. That stands for Charge, Parity, and Time. It says that if you multiply the charge of every particle by -1 (so positive charges become negative and negative become positive), flip space as if in a mirror so that your left and right sides are reversed (a "parity inversion"), and reverse the direction of time, then all the laws of physics are left unchanged.

Scientists had previously observed a violation of CP. That is, swapping only charge and parity is not an exact symmetry of the universe. If CPT is an exact symmetry (which scientists generally believe), that implies that T is not - changing only the direction of time without also swapping charge and parity should change the laws of physics. But testing that experimentally turned out to be very hard to do. Well, they've finally done it. And the results are exactly what people expected: it appears that CPT really is an exact symmetry of the universe.

Re:What this means (0)

patchouly (1755506) | about 2 years ago | (#42034951)

Great description! Thanks for taking the time to write this out. If I had any mod points, I'd be giving one to you!

Quick question then (1)

gr8_phk (621180) | about 2 years ago | (#42035283)

In a Newtonian universe, light will follow the same path backwards if it's direction is reversed (bounced perfectly normal to a mirror). My question is "does this hold under relativity?". I thought the answer was yes, but IANAPhysicist so don't know if that's the accepted answer. If it does hold then there are some very interesting consequences that are never talked about.

Re:Quick question then (1)

ceoyoyo (59147) | about 2 years ago | (#42035693)

Since photons do not routinely experience CP violation they also behave the same way forward and backwards in time.

Re:Quick question then (4, Informative)

arth1 (260657) | about 2 years ago | (#42036137)

Since photons do not routinely experience CP violation they also behave the same way forward and backwards in time.

Well, photons don't experience time in either direction. Those who experience photons do, but to a photon, no time can pass because they by definition move through vacuum at c.

It also has no antiparticle (or, you could say, it is its own antiparticle), so there's no way to reverse time even if you managed to prolong the subjective lifespan of a photon beyond instantaneous.

Re:Quick question then (2)

SoftwareArtist (1472499) | about 2 years ago | (#42036107)

Yes, and not just photons. Any particle will follow the same path backward, as long as you also reverse its charge (which has no effect on a photon, since they're uncharged) and parity (which I think flips the polarization of a photon, but don't quote me on that). What CPT invariance really says is that there are two ways of describing the universe that are exactly equivalent in every way. They predict exactly the same result for any experiment you can ever do. But what one description calls "forward in time", the other one calls "backward in time".

Re:What this means (0)

PiSkyHi (1049584) | about 2 years ago | (#42036225)

I don't think the reversing the syllogisms holds in this example. It is not sufficient to say that because T is violation that T would not be in violation if the universe were flipped and all CPT were now opposites. Just managing to show that things do not reverse equally in this universe, does not mean that by inverting everything, you also invert false to true.

I think you have misunderstood the implications of this finding. Just like gravity waves and their observation (or lack of), I think it only takes a small philosophical thought experiment to realise that there are problems with the questions being asked here and so the results alone will only serve to confuse.

For a start, let's assume that time is a dimension - this is an assumption that most physicists hold dear, some do not.
In this circumstance, the arrow of time appears arbitrary since positions in a spatial dimension appear arbitrary - it could this far along and a sequence of actions moved it in this direction, reversing all the actions perfectly moves everything the other way.
Of course, even if this were definitely true, you would still be faced with the dual direction problem - i.e. it looks like if time is a dimension, then it runs the same way forward as backward - as long as actions are reversible. This is just another way to say that time itself is static, the chosen direction itself is arbitrary and one could say that in a inverted universe my reverse is your forward. What I'm really saying here is that if time is a dimension, then the real problem is having a universe where time runs both forwards and backwards in different regions of space and that it would be possible to observe one from the other. This violates relativity.

So, if time were not a dimension, merely a product of components of the universe being able to interact consistently with other components of the universe (i.e. for this to happen, you need causality and change), then it would appear to have a direction to observers too small or slow, but this would be an illusion because the observer can not exist outside of the realm being observed. It's like a physicist is doing a thought experiment without realising he doesn't actually exist outside of the realm he is imagining to be our universe.

Time is a process - Time has no direction at all because it is the process of change that allows observers to do anything at all, imagining it running another direction is actually happening in this universe. Time is the result of a universe struggling with a paradox of it being one solid indivisible thing, or a multitude of things that appear to interact. If it contains components, they require time to observe each other with consistency, being the result of the causality required to keep things consistent. If there were no relativity, the universe would have no discernible objects and its only consistency would be to remain a single, solid unchangeable, unobservable thing.

so CPT invariance implies that the universe is the same thing, just being viewed differently - you still can't run it forwards and backwards in different regions of space and this whole thing of it being viewed differently is just a thought in someone's very real head that also cannot run time differently - it cannot be "viewed" from outside at all. I nearly said you can't run time forwards and backwards in the same universe, at the same time! But of course, the absurdity of that just illustrates that some questions are just improperly formed and do not have meaningful answers because the questions themselves are self-inconsistent and meaningless.

The Ugly Details (4, Interesting)

Required Snark (1702878) | about 2 years ago | (#42035039)

If your follow the links far enough you get here http://physics.aps.org/articles/v5/129 [aps.org] where they have a detailed non-mathematical description of the experiment.

After detecting and identifying the mesons, the experimenters determined the proper time difference between the decay of the two B states by determining the energy of each meson and measuring the separation of the two meson decay vertices along the e-e+ beam axis. When time-reversed pairs were compared, the BaBar collaboration found discrepancies in the decay rates. The asymmetry, which could only come from a T transformation and not a CP violation, was significant, being fourteen standard deviations away from time invariance. Thus the long wait for an unequivocal time-reversal violation in particle physics is finally over.

IANAP, but here is my understanding of the experiment. They knew that two different decay chains occur from some positron/electron collisions. If time is symmetric, there should be equal numbers of both chains. By making the beam energies different between the positron and electron (e-e+) beams, they were able to differentiate the decay order. If time symmetric decay occurred then there would be one spacial pattern in the results, and if time was asymmetric there would be another. The results conclusively show that for this subatomic event time runs in the direction we know as "forward". This is a big deal for subatomic physics.

larger question. (0)

Anonymous Coward | about 2 years ago | (#42035153)

Yes but the larger question is. What is it pointing at?

Am I Getting This Right? (0)

Anonymous Coward | about 2 years ago | (#42035835)

So, if I paint something and then smash it, the out come will be different than if I smashed it and then painted it. Thanks, science.

DeLorean (0)

Anonymous Coward | about 2 years ago | (#42036057)

next test, tomorrow at Twin Pines mall...

tsop tsirF (5, Funny)

waynemcdougall (631415) | about 2 years ago | (#42036153)

emit fo worra diputS

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