×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# faster than light3

## faster than light

(OP)
It is a commonly taught that the phase velocity propogates at a velocity > the speed of light in waveguide systems. However, with the caviot that the information travels at the "group velocity", which is equal to or slower that the speed of light.

Question? by using multiple channels or waveguides, quantum detection and combinational logic, could an effective information "packet" be synthesised from the combination of phase velocity transmitted energy? and faster than the conventional group velocity.

The application is be encription keys that are imbedded into leading edges of com signals.

### RE: faster than light

I don’t think it is fair to say that the phase velocity "propagates". The phase velocity is a virtual velocity, not an actual velocity, and I don’t believe it is of any practical use in terms of information transmission.

Regardless of the phase velocity, when you change the modulation at the sending end, the modulation will not reach the other end faster than the speed of light.

You may be aware of real time scopes where the write speed across the screen exceeds the speed of light. Nothing is travelling faster than the speed of light of course, its just that the beam appears to be going that fast.

### RE: faster than light

2
Let's suppose I have a poverfull laser. I rotate it at 1 rev/sec. 1 million miles away the light spot will "move"
6.28 million miles per sec.

The phase velocity is not real - it is comparing the
peak times at different places like the different light spots at differen places -- motion would mean the SAME
light spor or amplitude moving.

### RE: faster than light

(OP)
Ah, Yes causality. We were taught that to. Does not a unit step pulse in the frequency domain introduce time sidelobes into both + and - time domains? What ever made you think quantum systems were causal?. Now my ruler sees a spot of l8ight moving faster than light. Now you tell me that light is moving faster than light. Better get your story straight. You are not making any sense.

### RE: faster than light

Nbucska is quite right, and his thought experiment with the laser demonstrates the “faster than light” scope trace very nicely. Think of the light photons as little bullets. Each one is travelling at the speed of light. The apparent faster than light speed of the beam sweeping across the distant screen is not due to any individual photon breaking the light barrier.

Please try to quell your annoyance because you did not understand the answer. We are freely giving our time and there is no need to be rude.

### RE: faster than light

(OP)
Funny thing about your "bullets", the harder you try to pin down there position or velocity, the opposite is harder to determine.

Say there are two points on nbuska's circle. A and B. Point A makes precise position measurements. Point B make precise velocity measurements.

The precise position measurements at A also, strange enough, affect the bullet's velocity that are behind it as well, if the source is well known. Like predicting a bullets fly out to compute lead angle. The precision on the A point position accuracy is modulated-- modulating the velocity of the ones behind.

The velocity meter at point B detects this modulation (information)

Sometimes you need to kick a donkey to get it's attention.

### RE: faster than light

(OP)
Sorry to see that your post was removed xyzzy. Very interesting. Now you see, the pulsars were no accident. Better wake up humans, were coming!

### RE: faster than light

xyzzy pse send me your posting. Tnx.

### RE: faster than light

(OP)
wow, that was strange, I just noticed that the last part of my post disapeared. It was supposed to be:

Better wake up humans, we're coming!....

... to the end of another lame april fools joke.

Stars to logbook and nbucska.

nbucska, xyzzy was a magic word on the old unix main frame text based game adv(enture) that we engineers would play when knowbody was looking.

### RE: faster than light

GOTWW:
A better "Gedankenexperimente ":

From a plane I observe the trafic on Hwy 267. South of
Longont CO I see a schoolbus northbound.

2 minutes later and 10 miles north from this point
I see the/(a) schoolbus.

The speed is 10/(2/60) = 300 MPH.

### RE: faster than light

(OP)
So you are in a plane traveling 300 mph ~ 0.5 mach. Pretty good clip, must be a jet.

Gedankenexperimente ": german?, definately not spanish.

Ukrainian Proverb;" In every joke there is a truth"

A wave hits a beach at an angle, the the velocity at which the wavefront intersects the beach is faster than the velocity of the wave front normal to it's propogation vector. QUARK! phase velocity!

Can a disturbance at the instant this wavefront "hits" the beach propogate parallel the wavefront, along the crest?
This disturbance travels along the wavefront. The effect of the disturbance travels a physical distance farther than the actual distance traveled by the wavefront! Quark! a disturbance on the phase velocity!

xyzzy was a magic word that got you out of closed dark caves/traps. It did not always work.

My guess is that you got stuck and died in alot of those dark cold caves.

(I did also, as I said, it did not always work).

### RE: faster than light

I recall reading about a group of physicists (in Germany, I think) who managed to send a (Beethoven's 5th) signal faster than light. The concept was to use quantum tunneling of electrons through a copper sheet, but the result was hotly debated. I am not sure of the current status of that experiment.

This does rather strike a chord though. Using only Maxwell's equations (which are after all the foundation of relativity), only v<c siganls are possible. In order for anything to have any chance of travelling faster than light requires a quantum style solution.

Don't get me wrong (I'm convinced string theory, or even membrane theory will eventually prove to be resonances in spacetime), I'm not saying the solution will require spooky quantum laws. I'm just saying that we will need to understand quantum mechanics better before we can try stuff like this.

Still, good to think outside the box...

Mart

### RE: faster than light

Doing a google search, I found the following link. If you download the PDF, then look up (under entry "c") "speed of light in ambient vacuum", there is some good info.

http://www.intalek.com/Index/Projects/References/glossary1.pdf

Towards the end of the entry, it mentions the quantum tunnelling experiment - apparently the signal can travel at 4c!! It also seems to substantiate the point I made about the need to understand and manipulate quantum physics in order to escape the light cone. This interests me, since I am curious, like many, about what sort of engineering could carry us (as well as our signals) to the stars...

Mart

Mart

### RE: faster than light

(OP)
I have become disillusioned with the concept. The problem is that when you decode a quantum message, the content is distroyed. only good for one on one com, and only if carefully coordinated. Say if you detect intellegent quantum disturbance in a pulsar flash, well the first one you reads it gets the info, but if it was not meant for you, then you distroyed someone elses message, not very polite. After all it may have been and SOS from CK getting attacked by the klingons

### RE: faster than light

The same could be said for line of sight communication - anything broader soon disperses the energy over these distances. Surely the concept of being able to send a signal closely resembling Beethovens 40th at v>4c must intrigue you? I would say it would be better used as part of a communications network, with quantum hub servers for v>c communication to "out there". Must admit I am more curious about the physics of it all, and whether it can be adapted to defy v<c for more massive forms of tele-interaction...

Mart

### RE: faster than light

(OP)
The solution is obvious enough, Quantum repeaters, Serial in serial out.... way out. You reconstitute what you just destroyed. Kinda makes things into a galactic party line. No secrets, for If you live in the glass house, or you are safely 2-billion light years away from the "insulted" party. I would guess that glacto-locating may be a bit of a problem also. This gives new hope to my planetary yig resonator concept, quantum surfers communications, and (almost)instantaneous plantary phones.

I better lie low for a while, of late I feel that they have been watching me.

### RE: faster than light

"I better lie low for a while, of late I feel that they have been watching me"

Hehehe. I gave up ages ago and just smile a lot for the cams...

I like your Quantum repeater idea. I don't think I was ever convinced about once only Quantum keys - just sounds good on talk shows!

Mart

### RE: faster than light

(OP)
Beam me up scotty. There was a big stir about the quantum pairs awhile back, have not heard much lately. Was it a flop, or is it now, the intellectual property rights of Exon-mobile?

### RE: faster than light

see my new post about Einstein.

<nbucska@pcperipherals DOT com> subj: eng-tips

### RE: faster than light

Just another twist on the laser light spot.
Instead of a light beam use a hypothetical wire or string.
Makes Nbucska's experiment very correct.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!