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Double-Slit Experiment in Time, Not Space
TheMatt writes "Thomas Young's double-slit experiment is a classic experiment that helped establish the wave-like nature of light. Since then, it has been done with atoms, buckyballs, and biomolecules. It has even been seen in a single molecule, and the single electron version was voted the most beautiful experiment by Physics World readers (covered previously on Slashdot). Now, PhysicsWeb is reporting that Gerhard Paulus and coworkers have conducted the double-slit experiment using a double-slit in time, not space. The "slit" was a crafted femtosecond pulse consisting of one-and-a-half cycles--say, two maxima and one minima--passed through an argon gas. Each maxima has a probability of ionizing an argon atom and producing an electron. The electrons were accelerated to a detector which observed an interference pattern since the detector had no idea which maximum produced the electron."
Just today at lunch I was saying "Wouldn't it be cool to craft a femtosecond pulse consisting of 1.5 cycles, say 2 maxima and 1 minima, passed through argon gas? We could get electrons which could be accelerated then observe the resulting interference patterns!"
Well, that didn't fly. The guys got pissed off and yelled "Shut up and watch the stripper!" so I sheepishly went back to my titties and beer.
Trolling is a art,
I know I'm probably going to be rated down for not being all-knowing, but could someone try to explain this in a bit more simplific terms? I know what the dual-slit experiment was, but I don't understand the purpose of this particular one.
I've been trying for years to do the double-slit experiment. Alas, the wife still won't go for it.
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Tjekke om adressen er stavet rigtigt. Bemærk at det har betydning, om du bruger store eller små bogstaver!"
that may as well have been the writeup, because i don't understand a word of it.
Do you guys get aspirine with your subscription? Cuz if you do, I'm signing up right now...
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
Not to mention flowers, too...
Obliteracy: Words with explosions
For those of you who are unfamiliar with the double-slit experiment, there is a very clear, non-technical explanation here.
This space for rent.
"In the classic version of the experiment, electrons pass through a mask containing two parallel slits and produce a pattern of bright and dark interference fringes on a screen." Wasn't this called Pong?
Relativistic time dilation has been demonstrated by synchronizing atomic clocks and sending one of them into space for a while at high speed. The one sent into space slows down a tiny bit. As I interpret this, one of the clocks is slightly in the past relative to the other one.
Suppose you did the same thing with two entangled particles. The particle sent into orbit be slightly in the past relative to the other one. So would they then be entangled across the dimension of time? Seems like this has big implications, though what they are is beyond me.
The very thought of making 5-femtosecond laser pulses (0.000 000 000 000 005 sec, right?) leaves me feeling dumb and slow.
That aside, someone please clue me in here:
So if the electrons hit the laser when the pulse was at maximum strength they would hit the detector, like the two "beams" of light passed through the slits in Young's experiment? and the ones that pass "between" the maxima and minima get distorted like the blurry edges of the light? thus making "slits" of electrons but at instants in time instead of separate points? (I'm no physics expert but I'm sure you guessed that by now...)
You can hold down the "B" button for continuous firing.
Im going to need alot of pot to understand this one.
The Code Ninja is swift with his tool, precise in his delivery, and deadly accurate in his execution.
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I thought the meaning of the double slit test was to prove that the single electron actually passed through both slits, and in essence interfered with itself.
But in this case we're dealing with two different electrons fired at different times, so it's not quite the same.
Even so, if the electrons create the interference pattern, that means they must have collided... in time? So the second electron reached the point of collision before it was actually fired.
Does that mean that every electron travels every possible path in space AND in time? So whenever it is possible for an electron to be fired, it does, and interferes with all other electrons fired at all other times?
My head hurts. Damn you, Science.
"Reactionaries must be deprived of the right to voice their opinions; only the people have that right." - Mao
Looks to be that they have redone the classic double-slit experiment in a new variation.
Instead of having the two slits existing at the same time but in different 3d space, they made the slits in different time, but in same 3d space.
Probably we have the same quantum effect as in the traditional double-slit experiment: When trying to determine which slit the particle passes through the interference pattern goes away, as the waves change change to particles.
It doesn't look to me like they have seen that experimentally yet. Their setup that did not produce the interference pattern looks more like a single-slit to me.
But I think that an attempt to find out at which of the two maxima are ionizing an argon atom should make the interference pattern go away.
I'd love to see a geometric illustration of how this demonstration is identical to Young's, rotated in spacetime.
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make install -not war
Basically, you can look at light, or electrons, or whatever, as either a particle or a wave. Sometimes one interpretation will work better (light as a particle explains the photoelectric effect, light as a wave explains interference patterns, diffraction, etc). Current state of play is that the wave interpretation is always the best way to look at things, except when you observe the system everything collapses to particles, and when something mathematically inconvenient happens (you can explain the photoelectric effect in terms of waves, but the maths is horrible).
Classic two slit experiment with light consists of shining laser light on a barrier with two slits; each slit produces a diffraction pattern (http://en.wikipedia.org/wiki/Diffraction), the diffraction patterns interfere to produce the classic two slit pattern, see same link. This basically works because the laser light is coherent, you can (sort of) treat all the photons coming from the laser like one photon.
If you do this with electrons, because electrons are waves, you get the same patterns. Ditto any other particle.
Even if you do this experiment firing only one electron at a time you will get the same two-slit interference pattern, although 'common sense' tells you the electron can only pass through one of the two slits what actually happens is it passes through both at once. If on the other hand you fit a detector over one slit to register the passage of electrons, so you can tell which slit the electron passes through, you lose the interference pattern, you get two overlapping single slit diffraction patterns, which is not the same thing.
Roughly, if you have two slits and whenever an electron is fired at the slits you do not know which slit it went through, but the classical probability (what you'd expect if you didn't know quantum mechanics) of either slit is 0.5, then you will get a two-slit pattern.
This is basically the same experiment, except instead of two slits in space a little distance apart there are two possible source times for the electron, separated by a small time gap. There is no way to know whether a detected electron was produced at the first or second time, so the maths works out (roughly) the same as for the two slits in space case and you would expect to see the classic two-slits pattern. But it is kind of neat that someone's actually found a way to test that idea.
...how can we turn this into some sort of weapon?
Proverbs 21:19
The experiment is the same as a known one, with a single difference: In the traditional experiment the slits are separated by a difference in the normal 3d space, But in this experiement the slices are at the same place in the normal 3d space but separated by a difference in time.
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**Skip the first part if you know the basics.
If you pass a water wave through a wall with two slits in it, you will get interference. If you put another solid wall (no slits) beyond and parallel to the first wall, you will see that the water line on the 2nd wall looks like a sinewave with magnitude tapering off as you get further from the slits.
If you pass particles (electrons, photons, etc) at a wall with two slits, and place a "detecting wall" beyond the first wall, then the distribution of electrons hitting the detecting wall would be similar to the wave observed against the 2nd wall in the water example.
--New Experiment--
In the new example, two pulses of light can trigger an electron to be released. Think of these two pulses as pulling a trigger on a gun while playing russian roulette. The electron is the bullet and the detector is your head. If you pulled the trigger at 0 secs and 2 secs, you'd expect to see a person die at 0.01 seconds and/or/neither 2.01 seconds, assuming it took 0.01 seconds for the bullet to reach the person and kill him.
The detector, however sees an interference pattern. This is like seeing deaths at 1 second or 1.5 seconds. The interference pattern is measured as a function of time, and instead of seeing two blips in time, they saw a range.
Cagle has been peddling this theory for quite awhile. Do a quick search on cagle in any of the sci.physics groups and you will see his posts along with extremely patient people who try to point out the flaws in his logic (cough!).
We defeated the Nazis, the next evil: Libertarians
Who is this "We" you refer to?
And since when do people who work hard to support civil liberties get lumped in with people who work even harder to take then away?
I think you need to spend a bit more time at Cato's website and learn what Libertarianism really represents. (Hint: diminished state control of our lives)
"Rocky Rococo, at your cervix!"
It's too bad more laypeople don't get into quantum physics, string theory, etc. The implicatisons are pretty amazing on both scientific and spiritual levels, and I have chosen to read much of what this science tells us as: The Universe (Multiverse) is One and Many simultaneously, we are all a part of it, and in essence, are all One. Time is an illusion on the ultimate level, as is the notion of our matter and energy being separate from every other element of the universe. Thus, death as we know it does not truly exist, when what you are is a focal point of the neverending Multiverse (God, if you wanna put it that way -- but that's up to you).
Gee... I wonder why they don't teach any of this stuff in the school system, unless you happen to go into phsyics?
I highly recommend The Tao of Physics by Capra (which I'm sure many scientists loathe). Also writings by Nick Herbert are pretty interesting. A lot of the stuff we are finding equations for now is what many indegenous cultures have taught for thousands and thousands of years. They may have communicated the ideas differently, but they strike me as having the same message.
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The techno-mediated cultural conspiracy
http://thewired.blogs.com/teotwawki/
Just a randomly picked response to this thread.
Here ya go:
www.timecube.com
There's gotta be a second or fourth corollary to Goodwin's Law here somewhere... mentioning the time cube guy....
The "slit" was a crafted femtosecond pulse consisting of one-and-a-half cycles--say, two maxima and one minima--passed through an argon gas.
Anyone who has a femtosecond pulse generator should feel comfortable with this. If not, get access to a two-photon UV femtosecond pulse generator which uses nanosecond-time-scale infrared laser to deplete the terminal state of an F2 laser, based on F2 transitions.
Next, you'll want a healthy dose of argon gas. Argon is used to reduce heat loss in sealed units by slowing down convection inside the air space. You can get argon gas cartridges to prevent wine oxidation, which is a neat little side benefit. A 50L cylinder filled with argon gas to a pressure of 10130 kPa at 30C has approximately 201 moles of argon. Just remember that if you're going to lase with argon, its most efficient transitions are at 488 nm and 514.5 nm.
So now you'll need to create an ion chamber using the argon gas. You'll need a metal conducting can, and a wire electrode in the center which is well insulated from the chamber walls. The chamber, of course, will be filled with argon.
Next, you'll need to use your femtosecond pulse generator to apply a DC voltage between the outer can and center electrode. This will create an electric field, of only a few volts, that sweeps the ions to the oppositely charged electrodes. For some additional fun, if you apply a few hundred volts, the electron emissions will produce "secondary emissions", which amplify the results. I wouldn't recommend creating one of these by hand if you haven't already done so, but remember to use a 4.7uF capacitor with non-polar film, a 100,000 megohm resistor and a 2N4117A electrometer-grade JFET.
Anyways, generating a local maxima shouldn't be too difficult if you keep the phase dynamics of your pulse generator within one half delta of the wavelength propogation delay of your argon gas cylinder. This, as always, varies according to room temperature, so be sure to calibrate your scales before attempting the experiment.
The trickiest part of the experiment is to build a ray tube to display your intereference pattern. I suggest using a Tektronix Type 453 Oscilloscope, which may be hard to find but has the best bang per buck.
In no time at all, you'll be generating double slits in time!
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No, time isn't a wave. As another poster mentioned, time is another dimension.
But it's much more tricky than that, time is very different from space. If you rotate a vector in 3-D space, it's length (x^2+y^2+z^2) will remain the same, even though the x,y, and z components are different and kind of mixed together. What Einstein showed is that in 4-dimension space-time, the quantity (-t^2+x^2+y^2+z^2) is what is conserved if you 'rotate' in 4-D spacetime (in other words, if you change reference frames, like going from standing on the ground to standing on a freigh train). So spatial dimensions look spherical while the time dimension looks hyperbolic.
There are obvious parallels between Space and Time in non-relativistic quantum mechanics, namely a time translation evolves the wavefunction by a factor exp(-i*H*t/hbar) and a spatial translation evolves the wavefunction by a factor exp(-i*p*x/hbar). What this means is that momentum is the 'generator' of space translations, and the 'Hamiltonian' is the generator of time translations.
But making relativity works in quantum mechanics isn't as straightforward as physicists hoped, and involved alot of extra work, which finally culminated as quantum field theory. You can read more detail here . But here's a quick summary :
In quantum mechanics, position and momentum aren't just parameters but are operators. They don't commute, which is why you cannot simultaneously know a position and momentum. But time is NOT an operator, it is a parameter, it's the corresponding Hamiltonian that is the operator. So you have 4-dimensional space, 3 dimensions act like operators, 1 dimension acts as a parameter.
So anyway, back to this experiment, what the physicists did was to show that an electron, with a probability of being created during two discrete times (each of the laser pulses) turns out to have an interference pattern just like photons traveling through two slits in space.
The resulting electrons weren't produced from laser pulse 1 or laser pulse 2, but were produced from a superposition of both pulses, and the complex phase that I showed previously with time evolution causes an interference pattern between the two pulses.
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We already knew that particles are also waves... What does this experiment show us that's new? Does it show that two particles are a wave, or something?
It tells us nothing new about waves and particles, but it does confirm that there is no difference between a pair of slits separated by space and a pair of slits separated in time.
IOW it confirms that time is just another dimension.
You make the mistake of thinking you can educate the fundamental stupidity out of people. You can't.
"Physics is cool and all, if you're not quite bright enough to make it in Math" "Physics is to math as sex is to masturbation." -R. Feynman
Interesting :) God has exceeded his 40 meg limit. I would never have thought of that myself.
Obviously only a Nazi would post a time cube link.
...
;)
(The real joke here will be clueless mods marking this as flamebait
"Mind, as manifested by the capacity to make choices, is to some extent present in every electron." -Freeman Dyson