Which is faster, Gravity or Light?

[Sociotard]

This is a weird thing I got to wondering today. I'm not even sure the question makes sense, but rep to whichever physics buffs think they know the answer.

 

Gravity is supposed to be represented by bends in the fabric of space right? a massive object moves over the fabric and the fabric bends. Fine.

 

Now, does the fabric bend instantly? or is there a rate at which it bends?

 

Put another way: an observation station is set up so that it is not in orbit (freefall) around the sun. It just stays in position using solar sails or rockets or something. It does so in order to both detect the suns gravity and the suns light.

 

Along comes a minor space god who yanks the sun right out from under us, hurtling it light years away. What does the stationary station notice first, that the sun's gravity is gone or the sun's light is gone?

[L. Marcus]

Re: Which is faster, Gravity or Light?

 

There was an experiment a couple of years ago that put the speed of gravity at within ten percent of the speed of light. It had to do with Jupiter occluding a star, as I remember . . .

[Clonus]

Re: Which is faster, Gravity or Light?

 

So far as we know, shifts in gravity propagate at the speed of light.

[pinecone]

Re: Which is faster, Gravity or Light?

 

Well...theory may have progressed since "back in the day". But it depends on what "gravity " is....if gravitons and the like exist then light seems like a reasonable "speed limit". But one way to look at gravity is the geometric distorion on space time from matter. And gravity is therefore a sort of information about the total effect of matter's placement and effect.

 

Well...I'm not explaining this very well, but information does not have a speed limit. So if the sun disapears, or doubles in size etc... the "information" arrives everywhere at a non known speed, but that speed could be infinate, and no "laws" I know of, would be broken.

 

This weird way of imagining things does "explain" while we can't find a "gravity particle".

Because there is not one to find, space time distortion is just a metric, no more "findable" than the "inches" particle....

[Comic]

Re: Which is faster, Gravity or Light?

 

Most current models and theories treat the "speed of light", c, not as the maximum "speed of light", but as the maximum speed of everything.

 

Nothing in this Universe travels faster than this c. Acceleration near c (i.e. at 'relativistic' speeds) has a nonlinear relation with the amount of energy required per unit of speed. At exactly c, any increase in speed would require infinite energy, which by definition is more energy than the universe contains. Ergo, the energy must come from some strange extra-dimensional source that has more than infinite energy to contribute to the speed of an object.

 

No interactions with anything faster than c would be possible in this Universe. In essence, the object going faster than c must leave the Universe, becoming intangible and invisible in all ways to this universe.

 

Also, any speed higher than c would travel backwards in time, and all things traveling backwards in time would do so at a speed higher than c. So nothing that travels backwards in time exists in this Universe.

 

Tachyons, for example, may exist. They just don't exist here, or if they do, they do in a manner that is intangible and invisible in all ways.

 

Luckily, comic-book physics don't obey these mathematical constraints.

[McCoy]

Re: Which is faster, Gravity or Light?

 

Newton says gravity is instantaneous, Einstein says it propagates at the speed of light. Neither one has been proven wrong yet.

[Nyrath]

Re: Which is faster, Gravity or Light?

 

According to current theories, gravity does propagate at "c", that is, the speed of light in a vacuum.

 

Of course, if you incorporate the timelag this imposes into, say, the Newtonian equation of the orbit of the Earth around the sun, it does not accurately predict reality. Actually, it predicts that the Earth would be flung out of orbit.

 

However, if you incorporate General relativity theory, you somehow arrive at the magic result of gravity acting like its velocity is infinite even though its velocity is c.

 

No, I don't understand it either.

 

http://en.wikipedia.org/wiki/Speed_of_gravity#Aberration_in_general_relativity.3F

[Clonus]

Re: Which is faster, Gravity or Light?

 

out the total effect of matter's placement and effect.

 

Well...I'm not explaining this very well, but information does not have a speed limit. So if the sun disapears, or doubles in size etc... the "information" arrives everywhere at a non known speed, but that speed could be infinate, and no "laws" I know of, would be broken.

 

 

If that were true then it would be possible to talk to the past and have it answer back.

[Inu]

Re: Which is faster, Gravity or Light?

 

I remember discussing this back when Generations came out, with the whole 'blowing up stars to remove their gravity to change the course of the ribbon' plot. We couldn't get a consensus among ourselves then, and stuff like this certainly don't help.

 

Personally, it makes sense to me that gravity should propagate at a particular speed, but then, it doesn't make sense to me that FTL should violate causality, and there seems to be something of an agreement on that one.

 

I just hope that better minds than mine can work it out, because this stuff just makes me want to cry.

[Badger]

Re: Which is faster, Gravity or Light?

 

The only thing faster than light is spicy food moving through my digestive tract.

 

 

Sorry, I felt a bad joke coming on.

 

 

Anyhow, I never really though of Gravity in terms of speed before. I feel so ashamed.

[Nyrath]

Re: Which is faster, Gravity or Light?

 

Personally' date=' it makes sense to me that gravity should propagate at a particular speed, but then, it doesn't make sense to me that FTL should violate causality, and there seems to be something of an agreement on that one.[/quote']

Well, technically you left out a step. You have to accept the validity of Einstein's relativity, which is (granted) almost universally accepted.

 

You see, relativity proves that FTL and time machines are two names for the same thing. And time machines open the possibility of violating causality.

 

If anybody cares, there is some more detail here:

http://www.projectrho.com/rocket/rocket3v.html#causality

[Inu]

Re: Which is faster, Gravity or Light?

 

Well' date=' technically you left out a step. You have to accept the validity of Einstein's relativity, which is [i'](granted) [/i]almost universally accepted.

 

You see, relativity proves that FTL and time machines are two names for the same thing. And time machines open the possibility of violating causality.

 

If anybody cares, there is some more detail here:

http://www.projectrho.com/rocket/rocket3v.html#causality

Yeah, I've had the pocket explanation before. I still don't get it. ; Most relativity examples posit are... well, I have a hard time putting them into physical space. But then, in relativity, 'physical space' is a fairly metaphysical concept. I just haven't seen any site that explains it slowly and carefully, step by step, in layman's terms... all of the explanations I've heard start out fairly simple, but then skip a few steps. I fully expect that some of the stuff I'm missing is, in fact, incredibly advanced mathematics that I don't have a hope in hell of understanding. I've done a lot of maths in my time, though I didn't continue it to university level, but relativity still leaves me reeling. I've seen the graphs -- but they all tend to come off to me like playing tricks with numbers, instead of representing anything 'real'. 'Look, we can make the numbers do this, therefore reality is like this!'

 

But since I haven't done maths, physics like the like since high school, I accept that my knowledge is limited and suck it up. =) But in games, I tend to ignore it anyway, mostly 'cause I like my FTL.

[Nyrath]

Re: Which is faster, Gravity or Light?

 

But in games' date=' I tend to ignore it anyway, mostly 'cause I like my FTL.[/quote']

You and everybody else

FTL: you the writer want it, your readers want it, everybody is doing it. I wouldn't worry about it, FTL is sort of a given in science fiction.

[John T]

Re: Which is faster, Gravity or Light?

 

Yeah, I've had the pocket explanation before. I still don't get it. ; Most relativity examples posit are... well, I have a hard time putting them into physical space. But then, in relativity, 'physical space' is a fairly metaphysical concept. I just haven't seen any site that explains it slowly and carefully, step by step, in layman's terms... all of the explanations I've heard start out fairly simple, but then skip a few steps. I fully expect that some of the stuff I'm missing is, in fact, incredibly advanced mathematics that I don't have a hope in hell of understanding. I've done a lot of maths in my time, though I didn't continue it to university level, but relativity still leaves me reeling. I've seen the graphs -- but they all tend to come off to me like playing tricks with numbers, instead of representing anything 'real'. 'Look, we can make the numbers do this, therefore reality is like this!'

 

But since I haven't done maths, physics like the like since high school, I accept that my knowledge is limited and suck it up. =) But in games, I tend to ignore it anyway, mostly 'cause I like my FTL.

I bought a book called "Black Holes and Warped Spacetime" when I was eight, and started programming calculators to handle the math for me when such calculators became available. I sometimes wonder which would make me more geeky - doing the math in my head, or programming the calc to do it for me...

 

Maybe the latter just makes me a LAZY geek...

[Comic]

Re: Which is faster, Gravity or Light?

 

Why is FTL impossible? To simplify, I'd like to replace FTL with >L.

 

This is one of the questions that gets much harder to solve if you look at the wrong end of it. It's very hard to explain the causality issue. It's easier to explain the energy issue.

 

In Newtonian Physics, or "the math used to explain most of the things we experience fairly well," a thing continues at the same speed until a new force acts on it to change its speed. Since theory is hard, and things we can really see are easy, let's also skip theory and stick with observations.

 

Let's ignore forces that slow things down, since we're interested in getting to >L speeds. This means we have to move in a vacuum, to not run into friction or collide with particles. We also have to move so far away from big things that the effect of gravity is too small to matter. These are the steps most sf are willing and able to take before they try >L, though they're not really necessary in Newtonian Physics, they 'just seem to make sense'. Since they reduce the clutter, we can go with them.

 

So, things we're talking about continue at the same speed until a force acts on them to increase their speed. In Newtonian Physics, so long as the mass of the thing does not change, the amount of force required to increase the speed by the same amount stays constant.

 

Newton called things of this type 'M' for short, and the force, for simplicity, 'F'. The change in speed (acceleration), he called 'a'.

 

One empirical fact observed, from Newton's time on, is that nothing (i.e. no M) was ever seen traveling past the speed of light. It became clear by experimental observation that this was not just the maximum speed of light, but the maximum speed of everything. We'll call the maximum speed of everything in vacuum 'c', because it's the first 'constant' measure that even climatologists and economists didn't dispute.

 

Of course, the problem became 'is there no way to travel >L, or have we merely failed to find one?' After all, until it was invented, we merely failed to find a way to make a lightbulb. It does us no good to ask 'have we merely failed to find a way to travel >L' if the answer to 'is there no way to travel >L' turns out to be yes. So let's drop the second part of the question, for now. If you're tempted to come back to it, remember it's just clutter and will only confuse the issue.

 

The speed actual light traveled in places (media) other than vacuum was lower than c, and it's known that when particles travel faster in a medium than the speed of light in that medium, a blue glow is caused and other observations happen that generally aren't expected. These observations would only clutter the discussion. They only involve things below >L speed, thus they don't matter to us now. So it's important to remember 'c' is not the same as the speed of light. It's the maximum speed of anything. If you're tempted to talk about special properties of light, remember it's just clutter and will only confuse the issue.

 

Also observed were the facts that adding more force (F) to something (M) at the speed of light © not only didn't make it go faster, it also didn't make it disappear. This meant that we didn't merely stop seeing M going >L, we really couldn't go >L in experiments. All that happened as F was added to M was the M changed color.

 

It had long been known that light, like sound, had wave properties. It also had particle properties. Leaping over the clutter, something new was happening near c that hadn't been noticed at lower speeds. At the speed of sound, for example, if you add more F, the sound doesn't go faster, but it also changes amplitude, not frequency or wavelength. (Depending on the media, it can generate overtones, but those are new sounds, not a change in the sound itself.)

 

Deliberately plotting the way F affected M, and measuring changes in the speed of any M as it approached c, physicists found that the relationship between F and speed as Newton discussed it was not enough to describe this frequency change. They found that near c, they had to measure the relationship between F and a function of (speed and wavelength). Since wavelength and frequency are inverses (they're related), I could have used frequency instead of wavelength, but theres enough f's in this already. It comes down to this: the nearer you get to c, the more wavelength change dominates and the less speed changes.

 

It seems odd to talk about the wavelength of a person, or of a ship, or of a planet, but if we don't overcome our hangups, we'll never travel >L anyway.

 

So, as c is approached, for the same amount of F, changes in speed decrease and changes in wavelength increase. I'm skipping the numbers, since there's a lot of them, and numbers aren't really needed if you have pictures. And there are pictures, if you go look. If you chart the relationship of F and speed as you get closer to c, then you find F goes higher and higher, and the line turns and becomes parallel to a line drawn through c.

 

Even if you add infinite F, you never touch or cross c. This is called a verticle asymptote (http://en.wikipedia.org/wiki/Asymptote). The conclusion of all of this is that, for everything that has been observed, there's no way to go faster than c.

 

Now, people talk a lot about Einstein and Relativity, and how his theory is an explanation that forbids this, or proves that. But even if you don't believe in or fully understand that particular theory, the evidence of measure and experimentation, experience and observation, add up to the more primitive conclusion: everything observed cannot pass c without using more than infinite F.

 

Since as far as we've observed, the patterns we've seen in the distribution of matter and energy in the universe suggests that there isn't an available source for more-than-infinite forces to propel objects.

 

Also, most things seek equilibrium (that is, if they have a lot of energy they try to get rid of it). The rate things settle to equilibrium can be charted, too. The bigger the difference in energy, the shorter the time it takes. Since we're looking for a greater-than-infinite energy difference, and the chart is also asymptotic for this rate of exchange, anything with infinite or more energy would give it off in zero time, based on observable patterns.

 

Which traps our proposed >L travel between existing for zero time and taking more energy than there is in the universe.

 

This means it just can't happen, unless everyone who's ever measured or observed everything happens to be wrong in exactly the same two dissimilar ways.

 

So, no theory, no numbers, no hard math. Just lists of things people have measured, and pictures of what the measurements look like when put together.

 

Of course, you'll have to take on faith that the measurements I say exist really exist, or go out and measure them for yourself. A good scientist wouldn't believe me.

[Cancer]

Re: Which is faster, Gravity or Light?

 

My memory is that there have been experiments demonstrating that gravitational effects propagate at c, but I'll have to do some library work to see what those were.

 

Violating c tends to do things like cause gross violations of energy conservation. Given that energy conservation was one of the key arguments for special relativity, it's almost axiomatic that in gravitation (general relativity) that speed limit is still observed.

[L. Marcus]

Re: Which is faster, Gravity or Light?

 

. . . For those who don't mind, there's a WikiPedia page on The Speed of Gravity. At the bottom, there are some experiments mentioned.

[Cancer]

Re: Which is faster, Gravity or Light?

 

Yeah, I feel stupid for forgetting. Hulse & Taylor's 1993 Nobel Prize in Physics was for showing that the orbital change in the binary pulsar followed exactly the rate predicted by general relativity. This isn't a direct measure of the speed of gravitation. But the rate of energy transport by gravitational radiation (which is what's causing that orbit to change) depends upon the speed of gravity wave propagation, and if that's not c, you don't get the agreement they saw.

[L. Marcus]

Re: Which is faster, Gravity or Light?

 

Bad Cancer! Bad!

[pinecone]

Re: Which is faster, Gravity or Light?

 

If that were true then it would be possible to talk to the past and have it answer back.

 

I don't know of anything that says we can't....Though I'm not saying that we can either...I remember reading some stuff about worm holes being turned into time machines years ago....Kip Thorne was involved it the speculation, and I trust his math skills.

Relativity is not Dogma though....anything not proved is still subject to dougt. We pretty much know that relativity is wrong....we just don't know How....or what to replace it with......

[John T]

Re: Which is faster, Gravity or Light?

 

Actually, based on some of the calls I've gotten at work, the only thing in this Universe that propagates faster than light OR gravity is stupidity...

 

And no, that's NOT a comment about any posts on this thread. Momentary segue.

[ghost-angel]

Re: Which is faster, Gravity or Light?

 

Actually, based on some of the calls I've gotten at work, the only thing in this Universe that propagates faster than light OR gravity is stupidity...

 

And no, that's NOT a comment about any posts on this thread. Momentary segue.

 

Stupidity propagates at the speed of light. It just got a head start on every other force in the universe so it's at the front of things.

[keithcurtis]

Re: Which is faster, Gravity or Light?

 

It would be cool if stupidity were faster than light. You could have spaceships fueled by stupidity.

 

"Scotty, we need more speed!"

 

"I'm sorry Captain! I canna do it. I've bought all the Amway and extended warranties I can, and I've got Reilly trying to get us into a land war in Asia!"

 

"Dammit Scotty, I don't want excuses! Exercise the option on the "Spock's Brain script!"

 

"That did it sir! Warp 11!"

 

Keith "I'd watch that show" Curtis

[assault]

Re: Which is faster, Gravity or Light?

 

It would be cool if stupidity were faster than light. You could have spaceships fueled by stupidity.

 

The Jupiter 2 would be faster than the Enterprise.

 

 

 

 

 

 

 

 

 

 

Tybo the Carrot Man.

[Sociotard]

Re: Which is faster, Gravity or Light?

 

*George Bush from the inside of the warp core* "Let me out, Let me out!"