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from the will-this-help-me-win-the-lottery? dept.
A team in Australia turned thought experiment into lab reality by using lasers. Their subject matter was not a photon but a helium atom. The lasers they used served as a pair of grates, one before the other, with the second grate randomly dropped in.
What they found is weirder than anything seen to date: Every time the two grates were in place, the helium atom passed through, on many paths in many forms, just like a wave. But whenever the second grate was not present, the atom invariably passed through the first grate like a particle. The fascinating part was, the second grate's very existence in the path was random. And what's more, it hadn't happened yet.
In other words, it was as if the helium particle "knew" whether there would be a second grate at the time it passed through the first.
Also covered at: phys.org. An abstract is available; full report is pay-walled. The original news article is at Australian National University
Original Submission
(Score: 4, Insightful) by Zinho on Thursday June 11 2015, @03:03PM
Can someone explain to me why time travel has to be involved here? My simplified understanding of QM for this experiment goes like this:
* the Helium atom is acting like a wave at all times, whether the grate is there or not
* in the absence of the grate the waveform collapses at the detector in a way consistent with the behavior we associate with particles
* In the presence of the grate the waveform collapses at the detector in a way consistent with the behavior we associate with waves
I don't see how this experiment adds any new insight over the double-slit experiment with photons beyond "yep, it works with atoms, too!".
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 3, Funny) by aristarchus on Thursday June 11 2015, @05:32PM
I don't see how this experiment adds any new insight over the double-slit experiment with photons beyond "yep, it works with atoms, too!".
Yes, but did you miss the part about the helium atom choosing what to be? We are now facing a world, with sentient helium atoms! And they apparently know the future!
(Score: 2) by Zinho on Thursday June 11 2015, @05:43PM
Yeah, I saw that line; I wrote it off as toning down the message for the lay audience. I take it from your tone that you find it just as ridiculous as I do.
For me, the whole "information transmitted back in time" idea for this experiment is a non-starter, and should have fallen to Occam's cutting room floor.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 2) by sjames on Friday June 12 2015, @03:33AM
The wording may have been dumbed down, but the experiment DOES show quantum non-locality in time as well as space. Occam never sought to reject objective measurement in favor of simplicity.
(Score: 3, Informative) by sjames on Friday June 12 2015, @02:53AM
Since the second grate doesn't exist at the time it passed the first one, the only way the presence or absence of the 2nd grate can affect that collapse is if the quantum wave is non-local with respect to time as well as space. While that has been suspected, even expected to be true, this is the experiment that demonstrates it to be true.
(Score: 2) by Zinho on Friday June 12 2015, @03:54PM
Since the second grate doesn't exist at the time it passed the first one, the only way the presence or absence of the 2nd grate can affect that collapse is if the quantum wave is non-local with respect to time as well as space.
(emphasis added)
False dichotomy detected. Actually, not even dichotomy; only one option is presented, and stated as exclusive to all other truths. Alternative explanation (not requiring time travel): the helium atom's behavior at the first grating is always invariant. Subsequent insertion (or not) of the second grating therefore doesn't change the physics at grating 1. It does, however, alter the behavior registered at the detectors because the second grating interacts with the helium atom's waveform if the grating is present, and doesn't if it is not.
You have inspired me to read TFA, here's what I've found:
“ The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wavelike or particle-like behavior was brought into existence,” Truscott said. If we are to believe that the atom really did take a particular path or paths, then one has to accept that a future measurement is affecting the atom’s past, he concluded.
(emphasis added)
Here's how I read that:
A is not true.
If A were true, it would require clairvoyance/time travel on the part of the helium atom
OK, so I believe them that the atoms don't, strictly speaking, travel from point A to point B. I can then also reject the time travel nonsense. This paragraph reads a lot like what I originally wrote, plus some text guaranteed to confuse people who don't believe that matter can act as a wave.
The abstract of the Nature article doesn't mention time travel at all. What it does say, is this:
Our experiment confirms Bohr’s view that it does not make sense to ascribe the wave or particle behaviour to a massive particle before the measurement takes place.
That fits with my understanding of wave-particle duality. Subatomic particles (and entire atoms, too, apparently) are odd things, and we can't think of them as bullets or ocean waves. Their reality is somewhere in between, and how they look to us depends largely on how we look at them.
I'm not trying to be obtuse or confrontational here, I just want to know if there's something I'm missing. I didn't find it in the linked articles. Where else should I be looking? I'm happy to read up some more if that's what it takes for me to really understand this.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin
(Score: 2) by sjames on Saturday June 13 2015, @12:14AM
What time travel? (Yes, I know the dumbed down version used that phrase but they were confused) The non-locality in space doesn't mean the particle jumps from wherever it happens to be to the point where the wave collapses, it just means that it's position was indefinite and then becomes known. Why should time be privileged in that regard?
So simply, the helium 'knows' the state grating 2 will be in because it is within that blurry region of space time that the particle 'calls' here and now.
If that interpretation bothers you, you'll HATE theirs. They are saying that the atom doesn't actually do anything when released, but then once it's measured, it RETROACTIVELY fell through the two gates but it 'knew' (was affected by) the state of grate 2 because that state was known at the time it's motion retroactively happened.
(Score: 2) by Zinho on Saturday June 13 2015, @11:45PM
Yep, you're right, I hate that second explanation. Yours I like better. I'm OK with having a broader "now" and "here" for the particle, and the second grate interacting within the "here" and "now" of the particle.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin