lgy@blake.acs.washington.edu (Laurence Yaffe) (01/23/89)
In article <19680@uflorida.cis.ufl.EDU> seeger@beach.cis.ufl.edu (F. L. Charles Seeger III) writes:
-
- I'm no physicist, but there seems to be the possibility of quantum
- interconnects that exhibit ZERO propogation delays. The idea is to
- create a macroscopic quantum state to interconnect a sender and receiver.
- When this quantum state is perturbed enough to jump by the sender, the
- state changes instantaneously across its entire extent. Therefore, the
- receiver can detect this change without a speed-of-light delay.
-
- [...] I'm suspicious that either things
- didn't pan out, or else it got classified.
-
- BTW,
- this is NOT prevented by Relativity Theory, which is valid for describing
- the large scale universe. Quantum Theory is required to describe many
- physical systems that a classical theory like Relativity can not handle.
-
- Charles Seeger 216 Larsen Hall
- Electrical Engineering University of Florida
- seeger@iec.ufl.edu Gainesville, FL 32611
Regrettably, this just doesn't fly. Quantum measurments can't
transfer real information faster than the speed of light.
Quantum mechanics (or rather quantum field theory) is consistent
with (special) relativity. "There ain't no free lunch!"
Since this is very far a normal comp.arch topic, I've pointed follow-ups
to sci.physics.
--
Laurence G. Yaffe Internet: lgy@newton.phys.washington.edu
Department of Physics, FM-15 Bitnet: yaffe@phast.bitnet
University of Washington
Seattle WA 98195seeger@beach.cis.ufl.edu (F. L. Charles Seeger III) (01/26/89)
I am cross-posting this between comp.arch and sci.physics. The topic arose on comp.arch, but the future progress of this thread certainly belongs in sci.physics. However, I wanted to alert comp.arch readers that there is a good bit more of this discussion to come, in case they are interested. Below, I will promise to post a rather long article on this subject. If any comp.arch readers can't get a sci.physics posting, you may request a copy from me via Email. If there are many of these requests, I will consider breaking netiquette a bit by cross- posting (Net Police: this is your chance for prior restraint!). The promised posting will have a subject line similar to "Quantum Inter- connections & FTL Signals? (long)." Note that follow-ups are directed to sci.physics. Also, note that I may need to break the promised posting up into several parts. A couple of days ago I made a contribution to the comp.arch thread regarding the TI announcement of quantum transistors. John Berryhill raised the problem of a sufficiently fast interconnect technology that would be required to utilize the purported speed of these devices (claimed to have possible switching speeds "1,000 times faster than today's best semiconductor devices"). To this question, I alluded to the possibility of quantum interconnects to bypass the speed-of-light barrier, and I requested that anyone with more recent knowledge than mine to please share it. Rather predictably, there were follow-ups and private mailings flatly claiming that this was not possible. However, none of these messages discussed, refuted or even referred to the evidence that this may, in fact, be possible. To be fair, one mail respondent did mention the EPR Paradox in passing, but did not mention any of the later developments, e.g. Bell's inequalities or the Aspect experiment. Hence, I am singularly unimpressed by these flat denials. Their statements may be true, but I think that the authors' confidence in them can be shaken by an examination of certain experimental facts. Certainly, the Aspect experiment should put a dent in the armor of anyone who believes in the locality of nature as implied by General Relativity. GR will still apply to cases where certain types of quantum interactions are not present. Nonetheless, many physicists are bothered by the results of the Aspect experiment. One of the mail correspondents asked me to provide a brief summary of the EPR Paradox and the Aspect experiment. Therefore, I will post such a summary to your nearest neighborhood sci.physics newsgroup in the next few days. I will tease everyone reading this with the assertion that the Aspect experiment proves to my and many others' satisfactions that nature exhibits "non-locality", a.k.a. space-like connections. These faster-than-light (FTL) effects do NOT prove the possiblity of FTL communication, however. I will also give references to several pertinent papers, including those of the Sussex group. Their work involves the use of SQUIDs with Josephson constrictions, which they showed to exhibit macroscopic quantum behaviour. Such macroscopic quantum devices MAY offer the loophole by which FTL signaling can be accomplished. FTL signaling across space is still prohibited, but the potential for application in computers is obvious. Here is an outline of the FTL quantum communication circuit: 1. Points A and B are joined by a single, macroscopic quantum device. Following the Sussex work, this might be a superconductor placed in an RF field (say 430 MHz). A and B may be on the order of a meter apart. 2. The sender at A perturbs the quantum device, causing it to change state. 3. The quantum state switches due to the perturbation at A. This change of state occurs throughout the device at the same time; hence, there is no propogation delay (due to speed-of-light) between the change of the quantum state at A and that at B. 4. The receiver at B detects the change of state in the quantum device, thereby receiving the signal from A. There are many possible problems with this. Clark's work at the Univ. of Sussex indicates that macroscopic quantum devices are possible. The paper that I have reports work on SQUIDs 1 cm in diameter. This seems to imply that part 1 is possible. I don't think anyone will, at least in principle, object to the possiblity of causing the device to change state (part 2). Personally, I am most worried about part 3, the condition that the state changes simultaneously throughout the extent of the device. Persons more knowledgable than I seem to have taken this as possible. Certainly, the Aspect experiment shows that this might plausibly happen. But, I have seen no papers claiming to show direct evidence for this. Finally, the objection will be raised that the receiver will perturb the quantum device such that no useful signaling can take place. I *think* that this objection can be met technically. Since the quantum state that we are contemplating is so large, its associated energy levels will be large. Further, it will be fixed in position. Hence, I suspect that an adequate signal-to-noise ratio might be obtainable. There are rather a lot of mights and possibles. Then again, as I said before, I'm not a professional physicist. I humbly invite anyone with expertise to tell us what is wrong with all this. I would particularly like to hear about references that discuss or refute the possibility of this kind of FTL communication. I am not interested in any more flat denials of its possiblity, whether from professional physicists or not, unless some "signal" is added to the discussion. Also, don't try to engage me in any arguments over physics. I am no authority, though I am will to quote or refer to other authorities. This is why I will include detailed references in my next posting (I spent a couple of hours last night digging them up out of my collection of papers). On the other hand, I would dearly love to see these references discussed, refuted, supported or updated. I will also appreciate the (polite) correction of any of my misunderstandings, misconceptions or misstatements. Until my next posting, Sincerely (figured I'd better say that), Chuck -- Charles Seeger 216 Larsen Hall Electrical Engineering University of Florida seeger@iec.ufl.edu Gainesville, FL 32611
jeffa@hpmwtd.HP.COM (Jeff Aguilera) (01/28/89)
>>Common sense is not all that common. -- Bertrand Russell.
No!
Common sense is not all that common. -- Voltaire