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7116 clicks; posted to Geek » on 08 Nov 2012 at 6:40 AM (5 years ago)   |   Favorite    |   share:    more»

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Light has two speeds, one of which can be infinite.

BarkingUnicorn: Light has two speeds, one of which can be infinite.

Wiki's primer on phase velocity

I'll see if I can do a mathless explanation. Basically, when you have a complex wave system (think in sound, like an instrument playing an A major note), the wave is not a pure sine wave, it's a jumbled mess, just look at any piece of music in some editing software. This jumbled mess of sound travels in a wave-like way at the speed of sound. The speed of sound in this example is the "group velocity" the speed at which the whole system travels in space.

There's a nifty fact about complex wave equations, though, one which was worked out by a guy named Fourier, is that no matter how messed up a waveform looks, you can express it as the simple sum of pure sine waves, given that you intelligently pick what the frequencies and the amplitudes of those sine waves are.

These pure sine waves, which, when added, give you the wave that you hear, also have a speed at which they travel through space, this speed is called the "phase velocity" and does not have to be the same speed as the group velocity.

What this article is saying is that the only part of light waves that have to obey the speed of light is the group velocity, because that's what actually carries the information.

Hope that doesn't make your head worse. I'm going to bed now, but I can try to do better tomorrow.

The strict interpretation would be that information cannot travel faster than the speed of light. We already know coupled quantum pairs make changes at a distance faster than light could travel. Anyway, this just sounds like a standing wave in a crystalline structure.

That's ludicrous.

They've gone plaid.

nmrsnr:
What this article is saying is that the only part of light waves that have to obey the speed of light is the group velocity, because that's what actually carries the information.

You're saying that the real wave is limited to C but can be expressed as Fourier analysis where some of the elements are not limited to C?

So THAT's what happens when you divide by zero.

This is not a dream... not a dream. We are using your brain's electrical system as a receiver. We are unable to transmit through conscious neural interference. You are receiving this broadcast as a dream. We are transmitting from the year one, nine, nine, nine. You are receiving this broadcast in order to alter the events you are seeing. Our technology has not developed a transmitter strong enough to reach your conscious state of awareness, but this is not a dream. You are seeing what is actually occurring for the purpose of causality violation.

dittybopper: [1.bp.blogspot.com image 640x360]

This is not a dream... not a dream. We are using your brain's electrical system as a receiver. We are unable to transmit through conscious neural interference. You are receiving this broadcast as a dream. We are transmitting from the year one, nine, nine, nine. You are receiving this broadcast in order to alter the events you are seeing. Our technology has not developed a transmitter strong enough to reach your conscious state of awareness, but this is not a dream. You are seeing what is actually occurring for the purpose of causality violation.

That movie sucked.

Frederf: nmrsnr:
What this article is saying is that the only part of light waves that have to obey the speed of light is the group velocity, because that's what actually carries the information.

You're saying that the real wave is limited to C but can be expressed as Fourier analysis where some of the elements are not limited to C?

Not quite. Without getting into the heavy relativity type stuff, he's saying that individual (frequency) components of a complex waveform don't necessarily have to propagate at the same velocity as the overall waveform. Fourier analysis is just a tool for identifying which frequency components are present.

Phase velocity is a strange concept.

agent00pi: Frederf: nmrsnr:
What this article is saying is that the only part of light waves that have to obey the speed of light is the group velocity, because that's what actually carries the information.

You're saying that the real wave is limited to C but can be expressed as Fourier analysis where some of the elements are not limited to C?

Not quite. Without getting into the heavy relativity type stuff, he's saying that individual (frequency) components of a complex waveform don't necessarily have to propagate at the same velocity as the overall waveform. Fourier analysis is just a tool for identifying which frequency components are present.

Phase velocity is a strange concept.

Actually, disregard that. I just repeated you with different phrasing

/sleeps...

Light has two speeds, Engheta explains. The "phase velocity" describes how fast waves of a given wavelength move, and the "group velocity" describes how fast the light conveys energy or information. Only the group velocity must stay below the speed of light in a vacuum, Engheta says

Engheta! That's not right. The group velocity can also exceed c. (In which case, the information and energy-transport velocities are different from the group velocity.)

I'm sure he knows it, too. I wonder if the journalist misquoted him.

agent00pi: agent00pi: Frederf: nmrsnr:
What this article is saying is that the only part of light waves that have to obey the speed of light is the group velocity, because that's what actually carries the information.

You're saying that the real wave is limited to C but can be expressed as Fourier analysis where some of the elements are not limited to C?

Not quite. Without getting into the heavy relativity type stuff, he's saying that individual (frequency) components of a complex waveform don't necessarily have to propagate at the same velocity as the overall waveform. Fourier analysis is just a tool for identifying which frequency components are present.

Phase velocity is a strange concept.

Actually, disregard that. I just repeated you with different phrasing

/sleeps...

I love when science journalists are so desperate for someone to read their articles that they make outrageous bullshiat claims in the headlines.

Look for Jamie Condliffe's next article, "Scientists Discover Miracle Drug That Makes Humans Immortal". It's about the new fertility medication that Pfizer just patented.

Frederf: nmrsnr:
What this article is saying is that the only part of light waves that have to obey the speed of light is the group velocity, because that's what actually carries the information.

You're saying that the real wave is limited to C but can be expressed as Fourier analysis where some of the elements are not limited to C?

Basically yes, but I purposefully shied away from using the word "real" wave, since I'm not certain that the component frequencies are just a mathematical contrivance, they might have real ramifications of their own.

See "vector potential" as a concept that was created as a purely mathematical tool, but turned out to be real and detectable.

I really hate when journalists screw up science. C is the unassisted speed of light in vacuum. Of *course* light can go faster than C; for example if you were in a car traveling near the speed of light and turned on your headlights the light from your headlights would appear to travel away from you at the speed of light; making it goes 2C for anyone not in your car. This is considered 'assisted' light speed.

I realize it's sci-fi; but this is the basic idea behind Warp speed in Star Trek. The engines are always on the *back* of the ship and shine light *forward* so, even when it's going at the speed of light it can 'warp up' to 2C by lighting more bulbs on the engine (which is why they glow when they engage).

BigBooper: dittybopper: [1.bp.blogspot.com image 640x360]

This is not a dream... not a dream. We are using your brain's electrical system as a receiver. We are unable to transmit through conscious neural interference. You are receiving this broadcast as a dream. We are transmitting from the year one, nine, nine, nine. You are receiving this broadcast in order to alter the events you are seeing. Our technology has not developed a transmitter strong enough to reach your conscious state of awareness, but this is not a dream. You are seeing what is actually occurring for the purpose of causality violation.

That movie sucked.

No movie where Victor Wong had a prominent role sucked.

Fark_Guy_Rob: Of *course* light can go faster than C; for example if you were in a car traveling near the speed of light and turned on your headlights the light from your headlights would appear to travel away from you at the speed of light; making it goes 2C for anyone not in your car.

Um... no. Let's say you're driving your light-speed car towards Alpha Centauri. If you measure the speed of the photons leaving your headlights, you'll measure it at c. An observer, measuring the velocity of the photons when they arrive at Alpha C would also measure the speed of those photons at c. Now, the frequency of that light would be super blue-shifted, but the velocity would remain the same.

Wait... I just got trolled, didn't I.

BigBooper: That movie sucked.

Shut your mouth. That was the only movie, particularly that scene that freaked me the hell out at the time it was made.

I look forward to my ∞Mbps Internet service

Sounds like this could be used to make an awesome micro-flashlight.

BigBooper: dittybopper: [1.bp.blogspot.com image 640x360]

This is not a dream... not a dream. We are using your brain's electrical system as a receiver. We are unable to transmit through conscious neural interference. You are receiving this broadcast as a dream. We are transmitting from the year one, nine, nine, nine. You are receiving this broadcast in order to alter the events you are seeing. Our technology has not developed a transmitter strong enough to reach your conscious state of awareness, but this is not a dream. You are seeing what is actually occurring for the purpose of causality violation.

That movie sucked.

I have to disagree, for the most part... although perhaps this is a good movie allegory for the article. The movie as a whole - yeah, it wasn't the best. Its 'group velocity' was low.. HOWEVER, there were some parts of it that were just plain creepy and very well done.. its 'phase velocity' was quite good.

I remember watching that movie when I was in my teens, late one night, in the dark, completely alone. The dream-sequence part of it freaked me the -hell- out.

SirTanon: BigBooper: dittybopper: [1.bp.blogspot.com image 640x360]

This is not a dream... not a dream. We are using your brain's electrical system as a receiver. We are unable to transmit through conscious neural interference. You are receiving this broadcast as a dream. We are transmitting from the year one, nine, nine, nine. You are receiving this broadcast in order to alter the events you are seeing. Our technology has not developed a transmitter strong enough to reach your conscious state of awareness, but this is not a dream. You are seeing what is actually occurring for the purpose of causality violation.

That movie sucked.

I have to disagree, for the most part... although perhaps this is a good movie allegory for the article. The movie as a whole - yeah, it wasn't the best. Its 'group velocity' was low.. HOWEVER, there were some parts of it that were just plain creepy and very well done.. its 'phase velocity' was quite good.

I remember watching that movie when I was in my teens, late one night, in the dark, completely alone. The dream-sequence part of it freaked me the -hell- out.

I looked at that movie as a sequel to Legend. The hand coming out of the mirror reminded me of Darkness.

t3knomanser: Fark_Guy_Rob: Of *course* light can go faster than C; for example if you were in a car traveling near the speed of light and turned on your headlights the light from your headlights would appear to travel away from you at the speed of light; making it goes 2C for anyone not in your car.

Um... no. Let's say you're driving your light-speed car towards Alpha Centauri. If you measure the speed of the photons leaving your headlights, you'll measure it at c. An observer, measuring the velocity of the photons when they arrive at Alpha C would also measure the speed of those photons at c. Now, the frequency of that light would be super blue-shifted, but the velocity would remain the same.

Wait... I just got trolled, didn't I.

Nope. The light *HAS* to go 2C for you to see.

SirTanon: BigBooper: dittybopper: [1.bp.blogspot.com image 640x360]

This is not a dream... not a dream. We are using your brain's electrical system as a receiver. We are unable to transmit through conscious neural interference. You are receiving this broadcast as a dream. We are transmitting from the year one, nine, nine, nine. You are receiving this broadcast in order to alter the events you are seeing. Our technology has not developed a transmitter strong enough to reach your conscious state of awareness, but this is not a dream. You are seeing what is actually occurring for the purpose of causality violation.

That movie sucked.

I have to disagree, for the most part... although perhaps this is a good movie allegory for the article. The movie as a whole - yeah, it wasn't the best. Its 'group velocity' was low.. HOWEVER, there were some parts of it that were just plain creepy and very well done.. its 'phase velocity' was quite good.

I remember watching that movie when I was in my teens, late one night, in the dark, completely alone. The dream-sequence part of it freaked me the -hell- out.

Yeah, it's definitely a "sum of the parts is greater than the whole" sort of film. I do like it, though.

In a slightly related matter i have a question about this xkcd cartoon. I assume the cartoon is referring to the doppler effect but if you're really looking into a mirror that is facing the rear of the car wouldn't it technically be redshifting the light as it would be moving away from you? just curious.

auralpleasure: [imgs.xkcd.com image 229x284]

In a slightly related matter i have a question about this xkcd cartoon. I assume the cartoon is referring to the doppler effect but if you're really looking into a mirror that is facing the rear of the car wouldn't it technically be redshifting the light as it would be moving away from you? just curious.

The usual warning (because the passenger mirror is curved), is that objects are nearer than they appear. Edwin Hubble realized that more distant galaxies would be more red-shifted due to the expansion of the universe. So the distance between the Earth and distant galaxies can be expressed in terms of bluer (nearer) and redder (farther).

Which is exactly my point. if you're in the car traveling away from the objects in the mirror shouldn't they be redder because the light reflecting off of them is taking longer to reach the mirror than if the car was stationary and would be bluer if you were traveling towards the objects.

auralpleasure: Which is exactly my point. if you're in the car traveling away from the objects in the mirror shouldn't they be redder because the light reflecting off of them is taking longer to reach the mirror than if the car was stationary and would be bluer if you were traveling towards the objects.

They are redder, hence the warning that the objects are *BLUER* than they appear, which is another way of saying that objects that are red-shifted because you are traveling away from them are less red than they appear to be from your viewpoint.

/Duh.

dittybopper: auralpleasure: Which is exactly my point. if you're in the car traveling away from the objects in the mirror shouldn't they be redder because the light reflecting off of them is taking longer to reach the mirror than if the car was stationary and would be bluer if you were traveling towards the objects.

They are redder, hence the warning that the objects are *BLUER* than they appear, which is another way of saying that objects that are red-shifted because you are traveling away from them are less red than they appear to be from your viewpoint.

/Duh.

Thank you! It's so obvious now. I feel like a Coultard.

t3knomanser: auralpleasure: [imgs.xkcd.com image 229x284]

In a slightly related matter i have a question about this xkcd cartoon. I assume the cartoon is referring to the doppler effect but if you're really looking into a mirror that is facing the rear of the car wouldn't it technically be redshifting the light as it would be moving away from you? just curious.

The usual warning (because the passenger mirror is curved), is that objects are nearer than they appear. Edwin Hubble realized that more distant galaxies would be more red-shifted due to the expansion of the universe. So the distance between the Earth and distant galaxies can be expressed in terms of bluer (nearer) and redder (farther).

Except that, if I'm remembering my "Through the Wormhole" correctly, this has not been the case in practice. That in turn has led to the belief of "Dark Flow" I think they called it. An anology would be currents in the ocean. It adds to the idea that our universe is not isolated, but part of a larger multi-verse.

Also, someone explain to me how this couldn't be used to transfer information? Light on = 1, Light off = 0. It's like no one has heard of Morse Code before... Set up the parameters, and I don't see how this couldn't be used to transfer information, but please do correct me if I'm wrong.

justtray: Also, someone explain to me how this couldn't be used to transfer information? Light on = 1, Light off = 0. It's like no one has heard of Morse Code before...

What's Morse code?

justtray: Also, someone explain to me how this couldn't be used to transfer information? Light on = 1, Light off = 0.

Because group velocity, that's why.

agent00pi: Frederf: nmrsnr:
What this article is saying is that the only part of light waves that have to obey the speed of light is the group velocity, because that's what actually carries the information.

You're saying that the real wave is limited to C but can be expressed as Fourier analysis where some of the elements are not limited to C?

Not quite. Without getting into the heavy relativity type stuff, he's saying that individual (frequency) components of a complex waveform don't necessarily have to propagate at the same velocity as the overall waveform. Fourier analysis is just a tool for identifying which frequency components are present.

Phase velocity is a strange concept.

Ignoring some of the effects of relativity...

Imagine a bus travelling at exactly the speed of light. The bus is full of people sitting in front of one another. Let's pretend that everyone on the bus decides to do "the wave" and each person stands-up and sits-down, beginning at the back of the bus. That "wave" is travelling faster than the speed of the light, but the information is not, since it's happening in the bus.

Fark_Guy_Rob: I really hate when journalists screw up science. C is the unassisted speed of light in vacuum. Of *course* light can go faster than C; for example if you were in a car traveling near the speed of light and turned on your headlights the light from your headlights would appear to travel away from you at the speed of light; making it goes 2C for anyone not in your car. This is considered 'assisted' light speed.

I realize it's sci-fi; but this is the basic idea behind Warp speed in Star Trek. The engines are always on the *back* of the ship and shine light *forward* so, even when it's going at the speed of light it can 'warp up' to 2C by lighting more bulbs on the engine (which is why they glow when they engage).

Nice try.

The problem is the term faster than light, in terms of it being an absolute measurement of speed. By that definition light can not travel faster than light. If it did it would stop being light and become something else. To say light can have variable speeds then begs the question, what is the Speed of light and why can we not pass the speed of light.

If you drive your car at the speed of light and turn on the headlights, will they work? If so what is the speed of the visible light exiting the headlights?

shifter_: The problem is the term faster than light, in terms of it being an absolute measurement of speed. By that definition light can not travel faster than light. If it did it would stop being light and become something else. To say light can have variable speeds then begs the question, what is the Speed of light and why can we not pass the speed of light.

If you drive your car at the speed of light and turn on the headlights, will they work? If so what is the speed of the visible light exiting the headlights?

One would always measure the speed of light in a vacuum as c, no matter one's frame of reference.

pics or it didn't happen...

dittybopper: t3knomanser: Fark_Guy_Rob: Of *course* light can go faster than C; for example if you were in a car traveling near the speed of light and turned on your headlights the light from your headlights would appear to travel away from you at the speed of light; making it goes 2C for anyone not in your car.

Um... no. Let's say you're driving your light-speed car towards Alpha Centauri. If you measure the speed of the photons leaving your headlights, you'll measure it at c. An observer, measuring the velocity of the photons when they arrive at Alpha C would also measure the speed of those photons at c. Now, the frequency of that light would be super blue-shifted, but the velocity would remain the same.

Wait... I just got trolled, didn't I.

Nope. The light *HAS* to go 2C for you to see.

Trolled twice.

Professor Hubert Farnsworth: These are the dark matter engines I invented. They allow my starship to travel between galaxies in mere hours.
Cubert J. Farnsworth: That's impossible. You can't go faster than the speed of light.
Professor Hubert Farnsworth: Of course not. That's why scientists increased the speed of light in 2208 2012

/really? No one?

Ambitwistor: dittybopper: t3knomanser: Fark_Guy_Rob: Of *course* light can go faster than C; for example if you were in a car traveling near the speed of light and turned on your headlights the light from your headlights would appear to travel away from you at the speed of light; making it goes 2C for anyone not in your car.

Um... no. Let's say you're driving your light-speed car towards Alpha Centauri. If you measure the speed of the photons leaving your headlights, you'll measure it at c. An observer, measuring the velocity of the photons when they arrive at Alpha C would also measure the speed of those photons at c. Now, the frequency of that light would be super blue-shifted, but the velocity would remain the same.

Wait... I just got trolled, didn't I.

Nope. The light *HAS* to go 2C for you to see.

Trolled twice.

Ah, 2C, or not 2C. That is the question.

jaybeezey: Sounds like this could be used to make an awesome micro-flashlight.

If by flashlight you mean eye-destroying, matter-shredding hyperlaser, yes! It'd be a bit like having a fire hose or waterjet saw installed as a drinking fountain. In fact, since it would use light at phase velocity rather than group velocity, you could call it a phaser. Of course, by that logic, you could make a slow-light laser and call it a grouper.

Build a device to emit large amounts of such photons and attach an engine to move it to where you want before it detonates and you have a photon torpedo.

One assumes that either by using such superluminary photons, which would likely not actually work for lighting things at all since they'd tend to impart so much energy that they'd pass through or explode normal matter rather than bounce off of it, as a medium for information transmission, you'd have Star Trek-like "subspace" communications. Though really, using some form of quantum entanglement would be better for that sort of thing.

Now, if you could make a particle entangler/disentangler that works at a distance, you could create the ST transporter. No need for a Heisenberg Compensator, since using unilateral forced entanglement to impose a full-body pattern onto remote energy and matter would be the Quantum Silly Putty method of teleporting.

And if you entangled a superluminary photon burst to make a warhead with multiple or saboted phased explosions... Um. I dunno, quantum torpedoes?

P.P.S.: Warning!: Star Trek pseudophysics are toys for adults and should not be taken seriously by children, humorectomy patients or the developmentally impaired. While usual side-effects are mild, including but not limited to suspension of disbelief, bullshiat purchasing and light whatever, if taken too seriously they can lead to nerd rage, geek rage, hyperbolic superiority complex, anal inflammation and name-calling. Best taken with granular sodium chloride. In case of overdose or severe over-reaction, apply cold water and wet blankets along with real science and bed rest. Do not induce bile vomiting. Close cover before striking.

dittybopper: justtray: Also, someone explain to me how this couldn't be used to transfer information? Light on = 1, Light off = 0. It's like no one has heard of Morse Code before...

What's Morse code?

I'm still waiting for an answer. Is that some sort of computer thing? Like binary?

dittybopper: dittybopper: justtray: Also, someone explain to me how this couldn't be used to transfer information? Light on = 1, Light off = 0. It's like no one has heard of Morse Code before...

What's Morse code?

I'm still waiting for an answer. Is that some sort of computer thing? Like binary?

It's more like trinary.

<b><a href="http://www.fark.com/comments/7423220/80562832#c80562832" target="_blank">Smoky Dragon Dish</a>:</b> <i>dittybopper: dittybopper: justtray: Also, someone explain to me how this couldn't be used to transfer information? Light on = 1, Light off = 0. It's like no one has heard of Morse Code before...

What's Morse code?

I'm still waiting for an answer. Is that some sort of computer thing? Like binary?

It's more like trinary.</i>

You know I was being sarcastic. I was just waiting to unload on that guy.

And actually, it is like binary. For example, a C (-.-.) could be represented as
111]

dittybopper: <b><a href="http://www.fark.com/comments/7423220/80562832#c80562832" target="_blank">Smoky Dragon Dish</a>:</b> <i>dittybopper: dittybopper: justtray: Also, someone explain to me how this couldn't be used to transfer information? Light on = 1, Light off = 0. It's like no one has heard of Morse Code before...

What's Morse code?

I'm still waiting for an answer. Is that some sort of computer thing? Like binary?

It's more like trinary.</i>

You know I was being sarcastic. I was just waiting to unload on that guy.

And actually, it is like binary. For example, a C (-.-.) could be represented as
111]

I turned HTML off, and it still ate it. OK, now with spaces:

1 1 1 0 1 0 1 1 1 0 1

auralpleasure: [imgs.xkcd.com image 229x284]

In a slightly related matter i have a question about this xkcd cartoon. I assume the cartoon is referring to the doppler effect but if you're really looking into a mirror that is facing the rear of the car wouldn't it technically be redshifting the light as it would be moving away from you? just curious.

Yes it would that is why the object would be bluer than it appears. It has been redshifted so looks red but the object is bluer than that.

It would not appear bluer than it was it would BE bluer than it appears.

It`s like water. If you have a tank of water (laser) and you open one end (fire laser) then the flow goes at the speed water flows on land (speed of light in a vacuum) and you can move a water wheel with this (transmit information) and the max speed the water flows is at the speed of a very fast stream (30mph?). If you already have water there then a compression wave can travel fairly fast under certain circumstances but is not capable of doing work (500mph tsunami wave for example) yet the water itself can not travel so fast. This is how you have two speed limits.

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