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a1call
2008-Nov-16, 12:13 AM
*- Does Quantum Tunneling take place at FTL across a barrier?

Hornblower
2008-Nov-16, 12:44 AM
*- Does Quantum Tunneling take place at FTL across a barrier?
What or where is FTL?

a1call
2008-Nov-16, 01:09 AM
Apologies for the ambiguity of the used acronym:

FTL = Faster Than Light (http://www.acronymfinder.com/FTL.html)

Hornblower
2008-Nov-16, 01:58 AM
Apologies for the ambiguity of the used acronym:

FTL = Faster Than Light (http://www.acronymfinder.com/FTL.html)
In which case my answer would be, "No".

01101001
2008-Nov-16, 02:05 AM
What did the old BAUT Forum topics about quantum tunneling and group velocities (only) exceeding the speed of light, have to say? I think I recall several such topics, usually triggered by someone reporting another (or dusting off an old) faster-than-light claim.

Yeah, group velocity can move quicker than you might suppose. No, individual photons don't and you can't transmit information with the group velocity -- as I recall it always seems to work out.

I think a search of the forum or the Web will cough up a lot on this.

a1call
2008-Nov-16, 02:38 AM
Thanks for the confirmation.

I seem to recall vaguely from somewhere that like entanglement, quantum tunneling happens at FTL.

I did read up on wikipedia about quantum tunneling but no mention of FTL was given.

I understand these effects can not be used to transfer matter/info FTL (Macroscopically).

The reason I got curious is that I came across this article (http://www.witricpower.com/wireless-energy-transfer/5-moderate-distance-methods/5-1-evanescent-wave-coupling.htm) which seems to describe that some folks at MIT have managed to make a prototype of a wireless power transmission across some 2 meters using what is described at wikipedia (I think) as the electromagnetic equivalent of quantum tunneling.

I naturally got interested to know how would the impossibility of FTL info resolve if the said effect is indeed like quantum tunneling, an FTL effect.

Any insight into this would be greatly appreciated.:confused:

01101001
2008-Nov-16, 02:48 AM
I did read up on wikipedia about quantum tunneling but no mention of FTL was given.

I think there's more said in Wikipedia: Faster-than-light :: Get light to go faster (Casimir vacuum and quantum tunnelling) (http://en.wikipedia.org/wiki/Faster-than-light#Get_light_to_go_faster_.28Casimir_vacuum_and _quantum_tunnelling.29), and nearby:


There have been various reports in the popular press of experiments on faster-than-light transmission in optics most often in the context of a kind of quantum tunneling phenomenon. Usually, such reports deal with a phase velocity or group velocity faster than the vacuum velocity of light. But, recall from above, that a superluminal phase velocity cannot be used for faster-than-light transmission of information. There has sometimes been confusion concerning the latter point.

cjameshuff
2008-Nov-16, 03:09 AM
The reason I got curious is that I came across this article (http://www.witricpower.com/wireless-energy-transfer/5-moderate-distance-methods/5-1-evanescent-wave-coupling.htm) which seems to describe that some folks at MIT have managed to make a prototype of a wireless power transmission across some 2 meters using what is described at wikipedia (I think) as the electromagnetic equivalent of quantum tunneling.

It's similar, but wave behavior gives a better picture. My understanding is that it's actually the receiver's response that allows it to pick up the amount of power it does:

The transmitter normally can not radiate photons at the transmission frequency (a weak 1/r^2 far field), antenna geometry putting a kind of potential barrier in place, but the effect produced on the field by the receiver allows it to pick up power. A photon appears to show up out of nowhere at the receiver, but it can not do so before the "non-propagating" near field produced by the transmitter reaches it and can not be prevented once that has occurred, so information still only moves at c. Energy balances out due to destructive interference that reduces the power sent elsewhere.

This is just my very rough understanding, though. I'm no magician...er, RF engineer.

a1call
2008-Nov-16, 03:10 AM
Like I said I appreciate that very much 01101001.

That article is new to me and I will have to read up on it more carefully.

I do understand that the said experiment will end up not violating FTL but will need to figure out the actual mechanics of failing to do so.

BTW I am starting to suspect that you might be a Google Brain (http://www.youtube.com/watch?v=UC5DS0w9mJ4).:)

Please regard that as a geek's compliment.:doh:

a1call
2008-Nov-16, 03:15 AM
Thanks for the insight cjameshuff,

That does make sense.