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Author Topic: Physics question // Ansible?
Abyss
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Okay, so, I've been rolling this idea around in my head for a while, and now it's fallen out, and I'd like you to take a look at it for me and tell me if its any good. Especially if you know things about physics. Prizes include but are not limited to: FASTER THAN LIGHT COMMUNICATION.

Here we go:

Gravity is faster than light.

Well, technically, gravity doesn't have a speed. Gravity is constant. At all times, we are being affected by every 'gravitational field' in existence.

Crucially:

We are not more affected by 'fields' closer to us. We are not less affected by 'fields' further from us.

This is an illusion.

Centrifical force is mostly to blame.

But, more significantly, the ubiquitous nature of matter in the universe is to blame: there is a roughly equal amount of matter on all sides of us at all times. Roughly infinite, to be roughly precise. This makes the fields closest to us matter the most, since we are close to them. But even when we stop falling away from the Earth and start falling towards, say, the moon, or the sun, we are not "less" affected by the Earth's gravity or "more" affected by the moon or sun, we are just closer to one or the other.

What we call 'gravity' in these situations is really a by-product of proximity. And in a practical, Newtonian sense, of course we're affected more by gravity that we're closer to. That model works fine for, say, getting to the moon. But in a truer sense we are being pulled in all directions equally by the entire universe.

And, if we could parse that infinite tug, we could communicate faster than the speed of light. By wiggling a gravitational field on one end of the galaxy, and then noticing the wiggle (instantly) from the other side of the galaxy. Or, if we're evil, we could communicate FTL by blowing up planets.

So: if you'd like to send a message faster than the speed of light, all you should need is:

A) a device which measures all of that background gravitational pull.

... part 'A' is no small feat, true. Maybe it runs on a quantum computer or something. It would have some other interesting applications, though -- for example, it could give us a totally accurate picture of the universe, since its not bound by the speed of light, sidestepping the whole "all we see of stars is their old photographs", trillion-year-old starlight problem.

... let's call this gizmo a gravitrometer. Because, come on, haven't you always wanted to call something a gravitrometer?

and

B) something big (or dense) that you can move.

... the bigness/denseness required is directly related to the resolution of your gravitrometer -- if you've got a really good gravitrometer, you could communicate faster than light with, say, sign language. Hell, assuming that your gravitrometer is basically omniscient, you could just talk, and the gravitational wiggling of your vocal cords and the air volume differential in your lungs and throat could be extrapolated on the other side of the galaxy back into sound.

... for the purposes of this exercise, though, lets assume your gravitrometer isn't that good. It's only so-so. In that case, a black hole should do fine, assuming you can move it somehow. Compared to the incredible breakthroughs in science required for the gravitrometer to work, 'moving a really big thing' seems, really, way easier.



So, what do you think? Suppose I've got a gravitrometer and a black hole that I can wiggle back and forth. And suppose you've got another set on the other side of the universe. Did we just invent the FTL telegraph?

Would that work?

- Abyss

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Hobbes
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Gravity isn't faster than light, gravitational waves travel at light speed.

Hobbes [Smile]

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Samprimary
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http://www.qwantz.com/index.php?comic=1803
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PSI Teleport
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My husband's response to this topic:

"Huh. Gravity has lag."

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Nighthawk
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"Gravity doesn't exist. The Earth sucks."
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0Megabyte
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"The earth goes around wherever the sun was eight minutes ago!"

Hmm. Since I've never done the math, I've never quite understood why the various orbits had to be ellipses... but does this have something to do with it I wonder?

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King of Men
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quote:
Gravity is faster than light.
Wrong.

quote:
Since I've never done the math, I've never quite understood why the various orbits had to be ellipses... but does this have something to do with it I wonder?
No.
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Blayne Bradley
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Only under Newton did people think that if a planet dissappeared the universe would instantly know but this isnt the case, under relativity nothing travels faster then light, nothing, not even gravity.
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Abyss
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quote:
Originally posted by Blayne Bradley:
Only under Newton did people think that if a planet dissappeared the universe would instantly know but this isnt the case, under relativity nothing travels faster then light, nothing, not even gravity.

Well, that's a huge bummer. Who made light the king of speeds?

quote:
If gravity DID travel instantly, then we could send messages across arbitrary distances in a moment, and we'd call each other on gravaphones and they'd probably be heavy or something, I don't know! I AM JUST A GUY

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Blayne Bradley
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This should've been the first thing taught to you in high school science classes.

Math made it king of the hill, e=mc^2

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Blayne Bradley
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But we already have a possible solution for superluminal communication, google up quantum entanglement.
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rivka
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quote:
Originally posted by Blayne Bradley:
Math made it king of the hill, e=mc^2

Piffle. Math isn't something exists as a natural law or something -- it's a human attempt to describe the universe's behavior.
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Bokonon
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Quantum entanglement isn't going to get you faster than light communication, Blayne. Sorry.

Simple question: You and your buddy each have an entangled particle in a box, and you get into your spaceships and start flying away from each other... If one of you looks in the box/uses measures the entanglement (aka, sends a message), how does the other know that such an event has happened?

A hint to help point: there's no peeking in quantum entanglement scenarios.

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Orincoro
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It's so weird, I hear this pulp-science-fiction theory bounced around every few years by somebody with some difficulties understanding the implications of general relativity. Is it really impossibly hard for people to accept that you can't possibly send a message somewhere without also sending some amount of energy to that location, and that energy doesn't go faster than light does?

Whether it's the gravity thing or the quantum entanglement thing, it's always somebody failing to do at least one side of the equation. I feel like it's been too long since the nation had a good long Serious Science Documentary Series to set everybody straight.

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Blayne Bradley
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Well I was watching SyFy science and they focus on taking scifi concepts and finding how to the best of our theoretical ability making them plausible.

9/10 times the issue is either getting a huge amount of energy or a huge amount of an exotic but possible form of energy.

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Herblay
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Gravity as a force doesn't have "time", so it cannot be "fast". Like momentum, it's continual -- therefore the OP's (and Einstein's) assumption that it is a constant. But, yes, a gravity wave has a speed.

But theoretically changing a constant -- ie mass, gravity -- could provide an instantaneous form of communication, couldn't it? Suppose I could change the constant of mass throughout the universe a minute degree with an amount of modulation. If a sensitive enough device could measure that fluxuation. . . .

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mr_porteiro_head
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I think you'd first need to have a theory that explains how one could change the gravitational constant of the universe before you can say what changing that constant would theoretically do.
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Mucus
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Q
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Orincoro
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quote:
Originally posted by Herblay:
If a sensitive enough device could measure that fluxuation. . . .

Ask yourself how the nature of the device would be altered if the constant were altered as well.

For instance, if I were to try and send you a message by altering the speed of light by a minute degree, your speed of light detector would be looking at a light wave and measuring its speed. But the information regarding that speed would be relayed at... :drumroll: the speed of light. It's rather light attempting to weigh something on a scale where both sides are being added to at the same time- the effect is to cancel out any discernible change.

That and your modification of the constant, if such a thing were remotely possible, would also have to convey itself across the universe, and it would also do so at the speed of light- so if a discernible change were possible, say in the form of a wave, then that wave would be traveling at light speed.

A message must contain energy in order to be read. That is, it must have some energy at its endpoint that can be absorbed, thus changing something at the endpoint and conveying a message- a beam of light has to hit a charge-coupled device in order to leave a mark, that kind of thing. If your message is incapable of conveying energy to the target, then it cannot be read by anyone, and thus it has no effect, leastwise the effect of conveying a message. Energy apparently cannot exceed the speed of light, so you can't send a message faster than light.

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King of Men
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quote:
Gravity as a force doesn't have "time", so it cannot be "fast". Like momentum, it's continual -- therefore the OP's (and Einstein's) assumption that it is a constant.
To the extent that this makes sense, it is wrong. You are trying to describe physics without using math; this rarely ends in anything but tears.
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Bokonon
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To follow up, the gravitational constant (I believe) has a time component.

Ah yes: 6.67300 × 10-11 m^3 kg^-1 s^-2

That last bit (s^-2) means that gravity has a time component... Unless you are talking about some other gravitational constant.

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King of Men
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quote:
That last bit (s^-2) means that gravity has a time component
No. It means that the effect of gravity is acceleration, which is measured in change-in-speed (that's meters per second) per second.

You lot are trying to mix vague memories of high-school physics, which covered Newton's theory of gravity (which, as you ought to know, is wrong) with a discussion involving relativity. It won't work. However, if you remember the rubber-sheet analogy for Einstein's space-time, you can see what's going on. The Sun makes a big bump in the rubber sheet, and surrounding matter "rolls down into" the bump; that's the attraction of gravity. If you magically added mass to the Sun, it would take a bit of time for the rubber sheet to stretch so as to reach its new configuration; that's a gravity wave. The Earth would not notice the new attraction until the wave of re-adjustment had reached its orbit.

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Bokonon
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Yes, I realize that there was a more exact explanation, but why wouldn't the existence of time as a component (I don't know the exact term I am looking for) of G be enough to show that gravity does have time fundamentally woven into it?

Honest question, KoM, I'd be interested to know. The rubber-sheet analogy is useful in this regard, so thanks for refreshing my memory.

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King of Men
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quote:
But theoretically changing a constant -- ie mass, gravity -- could provide an instantaneous form of communication, couldn't it? Suppose I could change the constant of mass throughout the universe a minute degree with an amount of modulation. If a sensitive enough device could measure that fluctuation. . .
Well yes. And if you could travel faster than light, you could travel faster than light and wouldn't need to mess about with this ansible stuff. Since "changing X throughout the universe" and "travelling faster than light" are mathematically equivalent, I don't know why you'd mess about with the fundamental constants of physics just so you could beam pron to Alpha Centauri.

Look you, when Einstein says "You cannot send information faster than light", and you think you have a brilliant insight that shows how you can get around the limitation, the first step is to check whether your refutation begins "Assuming we can send information faster than light". All you've done here is to find a way to hide that assumption, provided you don't look very carefully.

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Herblay
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It's amazing how quick this board is to discount theoretically possible ideas (changing the gravitational constant, quantum entanglement) that most mainstream scientist don't discount -- at least for distant-future type theoretical discussion.

What methods would you folks postulate for a theoretically sound method of instantaneous communication, given a much futuristic technology set? Are there any more likely than those two? Maybe quantum foam or communication through created wormholes?

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mr_porteiro_head
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quote:
What methods would you folks postulate for a theoretically sound method of instantaneous communication
There you go using that word again. What theories are you talking about?
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King of Men
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quote:
Originally posted by Bokonon:
Yes, I realize that there was a more exact explanation, but why wouldn't the existence of time as a component (I don't know the exact term I am looking for) of G be enough to show that gravity does have time fundamentally woven into it?

First of all, because "time fundamentally woven into it" is a metaphor in the English language, not a physical quality. You could just as well say that gravity has strawberries fundamentally woven into it because the units of G are sv sb^-1 st^-2 where sb, of course, is the mass of a standard strawberry. (And sv is its volume and st is the time it takes to eat one!) And secondly, because those units are describing the effects on the target, not the force itself. They refer to the motion of the apple falling. I suppose you might say that motion has "time fundamentally woven" into it, but even so, you use up all the time units in G for the apple and have none left over for the force of gravity.

[ October 25, 2010, 01:43 PM: Message edited by: King of Men ]

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King of Men
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quote:
What methods would you folks postulate for a theoretically sound method of instantaneous communication, given a much futuristic technology set?
Why would I assume that such a thing exists? If we're speaking of theories whose experimental consequences have been demosntrated, there ain't no such animal. If we're talking about theories in general, I would suggest prayer. "Our Father, who art in Heaven; thy will be done. Please tell my brothers on Alpha Centauri that we were glad to hear from them last week, and that we hope Ixglugl's tentacle-rot gets better. The weather here continues fine..." Obviously an omnipotent god need pay no attention to the speed limit; who's going to give him a ticket?

quote:
most mainstream scientist don't discount
Citations needed. I think you'll find that what happens is this: There are two or three people who are willing to make qualified statements of a "Well yeah, theoretically, but you'd need a new theory of quantum gravity" nature; this gets written down as "A bit more work is needed and then we can insta-beam pron to Alpha Centauri", and then that gets quoted all over the blogosphere. And incidentally, I am a `mainstream scientist'.
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rivka
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quote:
Originally posted by Herblay:
that most mainstream scientist don't discount

They don't BOTHER to "discount" them -- there's no reason to consider them in the first place in any serious discussion.

quote:
Originally posted by Herblay:
at least for distant-future type theoretical discussion.

Would these be shoot-the-breeze-at-the-water-cooler type chats, or make-the-annoying-journalist-who-understands-no-higher-math-go-away type chats? Because I'll buy "mainstream scientists" accepting such notions for the purpose of either of those. Not for much else.
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Herblay
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Sorry, for context in my earlier argument, I meant changing the cosmological constant (not gravitational constant). And if the constant was changed universally, all solar bodies might behave unaffected, as relative to each other there would be no change.
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King of Men
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Ok, and this changes the underlying problem in what way? The difficulty isn't in coming up with constants to change, it is that you're just assuming away the lightspeed limitation! Again, when the thing you're trying to get around is "information cannot be moved faster than light", any argument that proceeds from "assume we can move information faster than light", however you hide that assumption, is just silly.
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Blayne Bradley
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Well you can travel faster then light, using the Alcubierre drive (Mexico's one and only contribution to the human race aside from food), but requires massive amounts of "negative energy" to get space to compress the way you need it to.

"Sci Fi Science: Physics of the Impossible" hosted by theoretical physicist Michio Kaku.

The premise is roughly taking impossible concepts from science fiction and finding ways to make it possible theoretically (if not practically).

For example, I never know in theory you could create a new universe/big bang if you superheated a single point in the vacuum of space.

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Herblay
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For some reason I thought that this topic was for a sci-fi story (though I don't know how I got that notion). I was trying to justify a plausible excuse for FTL communication -- not a rational scientific one.

Yes, as the idea was originally proposed, a change to an object's gravity would require time to reflect itself over distance.

But changing the cosmological constant wouldn't create a wave or a ripple. If it was possible, the entire universe would have to change simultaneously (or at least, it would have to change "together").

Take electron / hole flow for example. You aren't waiting for a single electron to pass through a wire, the electrons already exist throughout the wire. Propogation exists because ALL of the electrons (or holes) move together in the wire. Thus the time requirement is only the time that it takes for one hole to displace one electron. Or, imagine a string drawn through a pipe. Pulling on the string takes time, but motion at the other end is instantaneous -- because the whole string is moving.

In this case, the constant exists throughout the universe. You aren't waiting for a message to travel through the universe -- the whole universe is "moving", and the movement is the modulation of the message.

Please forgive an aspiring sci-fi novelist some level of speculation. I'm an electrical engineer, not a physics major.

[ October 25, 2010, 03:27 PM: Message edited by: Herblay ]

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MattP
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quote:
I never know in theory you could create a new universe/big bang if you superheated a single point in the vacuum of space.
How do you "heat" a "point" in a vacuum? Granted, I'm no physicist, but doesn't heat require matter and vacuum represent the absence of matter?
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mr_porteiro_head
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quote:
For some reason I thought that this topic was for a sci-fi story (though I don't know how I got that notion). I was trying to justify a plausible excuse for FTL communication -- not a rational scientific one.
If it's for a scifi story, I prefer the "we have this ansible, but we don't really understand how it works, just that it does, so just go along with it for the sake of the story, OK?" approach.
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King of Men
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quote:
Take electron / hole flow for example. You aren't waiting for a single electron to pass through a wire, the electrons already exist throughout the wire. Propagation exists because ALL of the electrons (or holes) move together in the wire.
Yes, there is a distinction between the movement speed of the electrons, and the propagation speed of the signal. You're talking about the latter, which nevertheless amounts to only about 80% of lightspeed. If you had a sufficiently long cable and applied a voltage to one end, you could measure the time it took for electrons on the other end to start moving. Such cables are of course quite rare, so usually we don't bother with the propagation speed.

quote:
But changing the cosmological constant wouldn't create a wave or a ripple. If it was possible, the entire universe would have to change simultaneously (or at least, it would have to change "together").
Yes, and this makes it possible because...? Again, the problem is that you're just assuming away the limitation you're trying to work around! "If I could propagate a change instantly through the whole universe, I'd have instant communications!" Do tell. And if you had a pony, you'd have some shoveling to do.
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King of Men
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quote:
Originally posted by MattP:
quote:
I never know in theory you could create a new universe/big bang if you superheated a single point in the vacuum of space.
How do you "heat" a "point" in a vacuum? Granted, I'm no physicist, but doesn't heat require matter and vacuum represent the absence of matter?
Just put energy into it; your photons or whatever will interact with the quantum foam. Probably. There's quite a bit of quantum field theory at the very smallest scales that hasn't been tested because we haven't got big enough accelerators. When people start talking about what might be possible with quantum foam and vacuum excitations and stuff, keep in mind that they are usually theorists who

a) Have made some simplifying assumptions because the real math is seriously hairy,
b) Assume that the theory confirmed by experimental results down to, say, 10^-18 meters will continue to hold at 10^-40 meters,
c) Are fairly confident that there won't be any experimental tests within their lifetimes, and
d) Love the sound of their own voices.

Observe that in point b, we have more than twenty orders of magnitude difference; that's bigger than the difference between regular 1-meter physics of the kind we evolved to understand, and quantum mechanics. There's a lot of room for new kinds of physics to be hiding in that sort of scale difference, as you can see.


Not to mention that just to see such effects in an accelerator, much less any sort of regular engineering object, you start talking about accelerator rings girdling the equator, or better still the Earth's orbit. (With little booster rockets keeping the magnets in place!) The synchrotron radiation losses increase as the fourth power (I think) of energy and decrease linearly with the radius, so you can see that pushing the energy up while keeping a constant radius becomes impossible at some point, and then the gains from increasing the radius are not that big.

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Bokonon
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quote:
Originally posted by King of Men:
quote:
Originally posted by Bokonon:
Yes, I realize that there was a more exact explanation, but why wouldn't the existence of time as a component (I don't know the exact term I am looking for) of G be enough to show that gravity does have time fundamentally woven into it?

First of all, because "time fundamentally woven into it" is a metaphor in the English language, not a physical quality. You could just as well say that gravity has strawberries fundamentally woven into it because the units of G are sv sb^-1 st^-2 where sb, of course, is the mass of a standard strawberry. (And sv is its volume and st is the time it takes to eat one!) And secondly, because those units are describing the effects on the target, not the force itself. They refer to the motion of the apple falling. I suppose you might say that motion has "time fundamentally woven" into it, but even so, you use up all the time units in G for the apple and have none left over for the force of gravity.
Fair enough. I hope my quantum entanglement/instant communication refutation post to Blayne didn't mangle the natural order too much [Smile]
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kmbboots
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quote:
Originally posted by mr_porteiro_head:
quote:
For some reason I thought that this topic was for a sci-fi story (though I don't know how I got that notion). I was trying to justify a plausible excuse for FTL communication -- not a rational scientific one.
If it's for a scifi story, I prefer the "we have this ansible, but we don't really understand how it works, just that it does, so just go along with it for the sake of the story, OK?" approach.
Me, too.
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HollowEarth
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quote:
Originally posted by King of Men:
If you had a sufficiently long cable and applied a voltage to one end, you could measure the time it took for electrons on the other end to start moving. Such cables are of course quite rare, so usually we don't bother with the propagation speed.

Actually, no such cables aren't all that rare. And it is easy to demonstrate with just about any cable you can find in the lab. A phase-sensitive detector is all you'll need to measure it. (Although a pulse source and a good scope would work too!)

When working in quadrature, if you need a tiny phase adjustment, one of the easiest ways to get it is to make one cable longer than the other, you get the phase shift since the propagation time is then different for each quadrature.

I'll forgive you this time, since you're just a theorist. [Wink]

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rivka
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quote:
Originally posted by HollowEarth:
I'll forgive you this time, since you're just a theorist. [Wink]

[Laugh]
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Samprimary
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Just in case anyone wasn't aware, this is why 'quantum entanglement ftl communication sfuasghsghasg' is so in vogue right now

http://www.youtube.com/watch?v=qwRcAeeaYlc#t=5m52s

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King of Men
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quote:
Originally posted by HollowEarth:
I'll forgive you this time, since you're just a theorist. [Wink]

I'm an experimentalist actually. You'll observe however that I was talking to an electrical engineer. I think they rarely care about phase effects. [Smile]
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