Posted on 06/16/2004 1:54:18 PM PDT by vannrox
TED: 2:55 pm EDT June 16, 2004
UPDATED: 3:03 pm EDT June 16, 2004
In a step toward making ultra-powerful computers, scientists have transferred physical characteristics between atoms by using a phenomenon so bizarre that even Albert Einstein called it spooky.
Such "quantum teleportation" of characteristics had been demonstrated before between beams of light.
The work with atoms is "a landmark advance," H.J. Kimble of the California Institute of Technology in Pasadena, Calif., and S.J. van Enk of Bell Labs in Murray Hill, N.J., declare in Thursday's issue of the journal Nature.
Two teams of scientists report similar results in that issue. One group was led by David J. Wineland of the National Institute of Standards and Technology in Boulder, Colo., and the other by Rainer Blatt of the University of Innsbruck in Austria.
Teleportation between atoms could someday lie at the heart of powerful quantum computers, which are probably at least a decade away from development, Wineland said. Although his work moved information about atomic characteristics only a tiny fraction of an inch, that's in the ballpark for what would be needed inside a computer, he said.
His work involved transmitting characteristics between pairs of beryllium atoms, while the Austrian work used pairs of calcium atoms. Each atom's "quantum state," a complex combination of traits, was transmitted to its counterpart.
Key to the process was a phenomenon called entanglement, which Einstein derided as "spooky action at a distance" before experiments showed it was real.
Basically, researchers can use lab techniques to create a weird relationship between pairs of tiny particles. After that, the fate of one particle instantly affects the other; if one particle is made to take on a certain set of properties, the other immediately takes on identical or opposite properties, no matter how far away it is and without any apparent physical connection to the first particle.
OK, here is the deal: I don't know what the deal is! To be more exact, the specific examples given here do not violate causality of their own accord but causality is violated nonetheless. Here, I'll explain.
This would be a lot easier if I could sketch it out as a visual, but I'll do the best I can (which isn't anything to get excited about..) First of all, in both instances - superluminal communication between 'stationary' locations or superluminal communication between locations moving apart at a 99% luminal velocity - we are only dealing with one inertial frame. Rather than think of temporal events along a unilinear progression, it is more apt to place them on a 'space-time' grid traversed by our two intrepid communicators.
Now, think of two parallel lines on that grid. The first line is earth and the second line is our starship moving away from earth at 99% luminal speed. Now, both lines begin on July 1 when our starship leaves the earth. As the starship bebops along into the great unknown, the effects of time dilation essentially begin to 'compress' time on the starship as observed from the earth's frame of reference.
OK, so now let's draw a line perpendicular to our two parallel lines. This line will represent our first superluminal communication. Now the point at which this line intersects Earth's temporal trajectory is July 4, but due to the time dilation effect, the intersection time on our starship is now July 3. OK, so our hysterical Earthling sends out her signal: "Terrible news! President Hillary Clinton assassinated! USA in mourning." Timestamp: 12:00 noon July 4. However, the time on your starship clock reads 12:00 noon July 3. You think to yourself, 'Oh, cool! I've already added a day to my life!' =)
Now, naturally, you send a signal back to Earth as swiftly as your trembling fingers can type: "Mourning?! Oh, please. Get a grip!" Now, let's draw another line across our grid perpendicular to our two parallel communicators to represent this subspace reply communique. As should be clear now, this does not create any causality problem. Indeed, Hillary-mourning Earth bimbo won't receive the message on her July 2; she's probably going to receive it on July 5 or 6!
The dreadful fallacy in that original post was precisely that: you fail to have NO privileged reference frames! Quite to the contrary, you alternate privileging one reference frame and then the other depending on who is transmitting a communication. Instead, our space-time grid represents the single inertial frame that encompasses both of our ansibles. It does not favor the reference frame of either. Instead, it represents the time dilation by progressively 'compressing' the movement of space-time at a given rate along the continuum of our starship as viewed from the vantage point of Earth.
You could accomplish the same effect by progressively 'elongating' the movement of space-time at a steady rate along the Earthling continuum as viewed from the starship's vantage point or by varying both rates as a steady function of one another. The relevant point being is that while our "instantaneous" superluminal communication does not in fact appear instantaneous to either as perceived by either vantage point, this is because the communique is itself exhibiting the perceptual time dilation effects instructed by special relativity.
It makes no difference if we instead conceptualize two ansibles on separate starships moving away from one another, because then we are merely replacing one inertial frame with another. The same is true if we are imagining two 'stationary' transmitters in separate star systems; they are operating along one inertial frame in relation to one another. The single inertial frame cannot twist in such a way as to make events in one locale's absolute future appear to be in that locale's past.
So, we've solved our causality problem, right? WRONG! As soon as another inertial frame is introduced - a third observer along a separate space-time 'trajectory' - *then* we've got the causality problems when they interact in tandem. So, basically what it comes down to is that we can only have one starship travelling at warp speed at any given moment - or else the universe collapses in a big crunch... =)
My solution is to declare that quantum mechanics is an incomplete theory. If that's good enough for Einstein it's more than good enough for me!!
Anyone should feel free to please correct any stupidity that crept into my post..
Anyone's. Of course, the fact that your clocks are slowing down is something you'd notice only if you compared clocks with some other frame of reference, as in the earlier example of the traveler who returns to earth and compares his clock with one that had originally been in sync with it before his departure.
And if the effect of any acceleration in any direction is to always see the other clock as slowing down, wouldn't that cause light from the other source to seem to be moving faster or slower than c (an effect that relativistic effects are supposed to cancel out, so that all parties always observe light from every source to be precisely c)?
Lightspeed is always seen the same, in all frames of reference. That's what makes it essential for clocks to slow down.
Disagreements in these things almost always involve misunderstandings about the various frames of reference. I think the ship and the earth are most definitely two different frames of reference. If you see them as one (because of their instantaneous communications system), this isn't unreasonable. Such a communications system would definitely throw everything that we know out the window. As observers in the same frame of reference -- neither is accelerating away from the other, and their clocks will remain in sync. Except it wouldn't happen that way.
I can't believe how many Firesign Theatre fans there are here. I could ask a hundred people I know and not one (outside of my family) would know about it.
The problem is that there are two reference frames in the problem, and events that are simultaneous in one frame of reference cannot be simultaneous in the other frame.
If we plot events on a grid where the x-axis is space and the y-axis is time as measured in one of the frames, we can use the same placement of the events as seen from the other frame, but the axes will be different for that frame. It's tricky to visualize, but the x and y axes will "scizzors" towards each other (meeting at the 45° line as the velocity approaches the speed of light).
[Geek alert: These coordinate systems differ by a hyperbolic transformation. There's another way to represent this that used to be more popular: if you multiply time by i, the square root of negative one, you can plot things in terms of this imaginary time quantity. Then the Lorentz transformation, as I describe it here, is merely a rotation. In other words, the coordinate systems of the two interlocutors are simply rotated with respect to one another in imaginary spacetime. This description, while mathematically equivalent, can be problematic for students, because while you can visualize time, and (with practice) a hyperbolic transformation, you can't visualize "imaginary time".]
You'll notice that the "travelling frame's" x-axis (which you can think of as the "axis of simultaneity") is now cocked at an angle in spacetime, with respect to the x-axis of the "stationary frame". As this axis of simultaneity is extrapolated back in the direction of the origin, it dips backwards along the time axis of the stationary frame. The more distant the conversation, the more pronounced the effect.
To recap: The Earthbound transmitter sends an instantaneous signal at time T to the traveller, who receives it at time T'. T and T' are simultaneous in the Earth's frame, but T' is simultaneous with a time earlier than T in the traveller's frame.
As long as the signal goes no faster than light, there's no way for the response to arrive before the first signal was sent.
I really should work out another example, along with some graphics that show explicitly what happens and why. If I do, I'll post it and ping you, but it won't be soon.
Maybe I cut back on my alcohol consumption too early...
I need a tooth pulled.....don't worry...we'll telleport all of you except your tooth.
Or how about...Man that guy sure has bad gas.Don't worry...we'll telleport him except for his butt.
Some old Physicist posts:
Just after the stroke of midnight on January 1, 3000, a tachyon beam signal, travelling at four times the speed of light, is sent from Earth towards the starship Tempus Fugitive. The message is "Ping!" At the time the message is sent, the ship is 0.8 light years from Earth, travelling at a speed of 0.8 times the speed of light.By the time the tachyon signal reaches the starship, it is 1 light year away, as measured from the Earth. But on the Tempus Fugitive, the Earth is only 0.6 light years away (Lorentz contraction).
The date of this event is April 1, 3000, just after 6:00 AM, as measured on Earth. But in the reference frame of the starship, this event is contemporaneous with events taking place on the morning of January 30, 2999 on Earth (frame dependence of simultaneity). [Geek alert: t' = gamma*t - L*beta*gamma/c; if t=0.25 years and L=1 l.y., beta=v/c=0.8, and gamma=1/sqrt(1- beta^2)=5/3, then t'=-0.9166 years.]
The Tempus Fugitive replies with an "Ack!" upon receipt of the message. It takes .15 years for the signal to traverse that distance, but the Earth is travelling away from the starship at .8 c, so the signal takes .1875 years or 68.4 days for the signal to reach Earth. But in the starship's frame of reference, time on Earth is moving only at .6 its regular speed, so only 41 days pass there (time dilation). The return signal arrives on Earth on March 11, 2999, almost nine months before the original message was sent.
153 posted on 09/30/2003 2:15 PM EDT by Physicist
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But that's my point: in order for FTL not to imply simple and gross time travel, the basics as we know them have to be very wrong.
Here's the fundamental problem: two distant events that are simultaneous in Earth's frame--say, the transmission and receipt of an infinitely fast signal--will not be simultaneous to the receiver if he's in a different frame. If the receiver is receding from the Earth, the "transmission" event takes place well after the "reception" event. The only way around it is for relativity to be totally wrong.
199 posted on 09/30/2003 4:16 PM EDT by Physicist
Thanks for the explanation. I think I'll go get some coffee, and see if I can read it again, perhaps comprehending some of it this time. :-P
That's certainly what Heisenburg states, but the nuances of it bring about all sorts of bizarre events. For instance, the fact that energy can be 'borrowed' to 'create' a virtual particle, which is then immediately annihilated. That is, unless you have an extremely strong field of some sort, such as a gravitational field. Heisenburg plus a black hole yields Hawking radiation, which blew my mind when I first read about it, and I've always been into particle physics. I still don't fully understand all the implications of Heisenburg, but I could have sworn that I read on NewScientist, or perhaps elsewhere, that Heisenburg was what prevents the use of quantum entanglement for communication purposes. My memory could certainly be failing me, and I'll have to see if I can dig up the article I'm thinking about.
If I remember correctly, time actually slows down as you approach c (speed of light in a vacuum). I believe that was one of the implications of special relativity. There's a reasonably simply equation for calculating it, which I toyed with during high school physics while everyone else was trying to figure out what the heck an electron was.
"Don't Crush That Dwarf, Hand Me the Pliers" - (Ralph Spoilsport of Ralph Spoilsport Motors, in the city of Emphysema...)
Oh dear, we're going to have 'issues'.. =)
From a causality standpoint, it does not matter if: "T and T' are simultaneous in the Earth's frame, but T' is simultaneous with a time earlier than T in the traveller's frame." What matters is that the traveller can receive no transmission at T'-x in reply to a transmission sent at T' and that the Earth can receive no transmission at T-x in reply to a transmission sent at T.
You are implicitly introducing a third reference frame interacting with the first two reference frames thereby creating a second inertial frame whereby the causal loop can be set up..
I already addressed the Lorenz transformation at the point I wrote that "the single inertial frame cannot twist in such a way as to make events in one locale's absolute future appear to be in that locale's past" [from that same locale's perspective]. That is the 'twist' to which I am referring to. Clearly I'm going to have to write another detailed post..
The conjectural tachyon communication is not relevant to the supposed quantum entanglement communication discussed here. Tachyons are in fact moving at superluminal velocities and have four-momentum; in short, relevant to causality, they are their own reference frame. In this "spooky action at a distance" quantum entanglement we're discussing, nothing is moving anywhere in the course of the FTL communication. Rather, you are extrapolating a series of actions upon the entangled particles at the other end by observing changes to the entangled particles on your end (which is somehow violating the No-Cloning Principle and creating an EPR Paradox, but let's not go there! ;)
For the first time physicists have forged quantum entanglement between two large blobs of gas. The achievement brings closer the possibility of super-fast quantum computers and teleportation1.
No. I just saved your post.
"Spike Lee just insulted me...but in Bizarro world, he said he likes my pants!"
- The Simpsons
BTW, this is SauronOfMordor's daughter. Fascinating subject, this is. Don't really understand it...but then, few people do.
In my version of that program it's all 9 of 9.
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