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Physicists Do What Einstein Thought Impossible
An anonymous reader writes "Einstein worked on Brownian motion (the movement of small particles in a fluid as they collide with the fluid's molecules) in 1905, but said it would be 'impossible' to determine the speed and direction of a single particle during this dance. Now researchers have gone and done it, by suspending a dust-sized glass sphere in air (which slowed down its dance moves, since it had fewer collisions with spaced-out air molecules than it would have had with water molecules). The researchers held the sphere in place with 'laser chopsticks,' and then watched how the glass bead bounced around to determine its direction and speed (abstract)."
You had me at "laser chopsticks".
It must have been something you assimilated. . . .
Laser chopsticks were invented to keep chow mein hot until the end of the meal.
I am the richest astronaut ever to win the superbowl.
How will the Infinite Improbability Drive work now? It depended on Brownian motion. Now probability can never come off 1:1 and it'll never work!
We must discover time travel immediately so we can go back and stop these researchers immediately! I mean, sooner!
Tomorrow is Towel Day! We cannot allow a travesty like this to stand.
"This post contains words, known to the State of California to cause thought. Wash brain thoroughly after reading."
In the way that a nice cup of tea is?
Best Slashdot Co
When people say "impossible" they generally mean "not possible given what I currently understand about XYZ"
Unless Einstein explicitly said "this will not be possible, ever"
I mean, heck the article demonstrates this itself:
"In 1907, Einstein likely did not foresee a time when dust-sized particles of glass could be trapped and suspended in air by dual laser beam “optical tweezers.”"
I'm sorry but: No freaking shit. In 1907 I doubt many people would have foreseen that
If you "hold it" doesn't that effect the out come of the experiment? Is this a bad test or just bad reporting?
Think Deeply.
Ha. Einstein. What an idiot.
This Einstein fella - I keep on hearing about how he's been proven wrong or might be proven wrong or how people are picking his ideas apart. It's like he hasn't even SEEN a modern physics paper in like, the last 50 years.
Google: "All your data are belong to us."
Einstein only said it was impossible from a tecnical point of view. Given he used brownian motion as direct evidence for the atomic/molecular nature of matter I am pretty sure he appreciated that with future technology it may be possible to do this kind of experiment...
If the glass bead were moving in such a way that was too subtle for them to measure, would they even know they couldn't measure it? What if Einstein was right and was simply implying that the movements eventually broke down so far that they were unobservable (similar to Planck's work)?
TFA doesn't refute any of Einsteins conclusions about Brownian motion. It only shows that it was something impossible to do at Einsteins time. What a cheap way to grab attention!
I've seen a couple of comments (more than one thread or else I would have posted a reply there) that seem to suggest that this breaks quantum physics by accurately predicting the speed and direction of particles, but it should be noted that the Heisenberg Uncertainty Principle states that it is impossible to accurately calculate both the velocity and its position. Speed and angle are components of velocity, therefor the only conclusion of this experiment is that velocity can be calculated under these conditions.
Since when is 'dust' a unit of size?
Since they made chopsticks out of monochromatic light.
This shows the onset from the ballistic regime into the diffusive one. They can resolve the motions of the glass bead from single collisions all the way up to a statistical ensemble of them (on which scale Brownian motion is observed). I.e. this has more to do with classical statistical mechanics than quantum mechanics.
there's no such thing as 'instantaneous'.
Never say never. Ah!! I did it again!
Exactly - they went and spouted "Oh, look at us, we disproved (Great Person X)'s work!" when all they really did was use selective reading and ignore the other half the book about the Uncertainty Principle
If you read the PhysicsWorld article, you'll see it actually says:
But he believed that it would be impossible in practice to track this motion, given the incredibly short timescales over which the Brownian fluctuations take place
Ahhh... still don't have the original source quotation from Einstein here, but it sounds like Einstein believed it was "impossible in practice" - in other words, that the technology didn't exist at that time to measure rapid fluctuations over microsecond or even nanosecond time scales, and maybe he couldn't even imagine such technology existing.
So he never actually said he thought it was beyond the physical limits of the universe. There was no proof or physical law involved.
Now call me up when somebody figures out how to move matter or information faster than the speed of light (i.e. group velocity greater than c). Einstein really did believe that was *impossible*.
One thing interesting that isn't mentioned specifically: This work, using "optical tweezers", is based on research done by Nobel Laureate Steven Chu's group at Berkeley. Dr. Chu also happens to currently be the US Secretary of Energy.
No job too big, no job too small, Steve Chu does 'em all.
this has got to be the coolest science ive seen on slashdot in a while. find a suitable nano-shark and we can start talking laser sushi.
Good people go to bed earlier.
Brownian Motion is a mathematical construct, which, among other things, is nowhere differentiable (almost surely). You can pin a BM down into sets with high probability, but no, you can't really predict it. It is merely used to *model* the movement of a particle in a fluid, it is not actually the process by which the molecules move. Indeed, "such a path represents the motion of a particle that in its wanderings back and forth travels an infinite distance in finite time. [BM] does not in its fine structure represent physical reality." (Billingsley, "Probability and Measure"). At least the science is interesting.
Yes, a letter i in your subject.
If I understood the article, what you saw at high school isn't all the motion that took place. So you couldn't use what you saw to measure the velocity of a particle. What you saw was limited by the speed of light and there are changes in direction and speed that happen between the instants you observe. That's as far as I can follow it though. I don't see, for example, why it isn't frequency that's relevant to measuring it. After all, you can sample other events occurring every 100ns at only a 20MHz frequency.
Unless Einstein explicitly said "this will not be possible, ever"
He did not - as you suspect what he meant was that it was "not possible with current technology" and certainly not that it was impossible in the same vein as "it is not possible to travel faster than light". It would be like someone today saying that it is impossible to build a 500PB hard disk - what they clearly mean is that it is impossible AT THIS MOMENT IN TIME to build a 500PB disk not that it will never, ever be possible to do so.
Of course being a famous physicist the media have no qualms about hyping it as if somehow they have done something that contradicts Einstein because it attracts attention and cannot be proven to be wrong even it is extremely clear what he really meant.