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The Speed Of Gravity Revealed
redwolfoz writes "New Scientist is reporting that the speed of gravity has been measured for the first time. 'The landmark experiment shows that it travels at the speed of light, meaning that Einstein's general theory of relativity has passed another test with flying colours.' Researchers made the measurement of the fundamental physical constant with the help of the planet Jupiter. One important consequence of the result is that it will help constrain the number of possible dimensions in the Universe."
Light has mass? no it does not.. the energy of a photon has a mass equivalence, but it does not have mass.
You're confusion arises because you were taught elementary Newtonian physics. In general relativity, one learns that any "information" cannot travel faster than light. Gravity is considered information because if you feel a gravitational force on you, you know that there is a body out there acting on you. That is, you have information about it (you could even estimate its mass by measuring the tug it exerts on you).
In Newtonian physics, lots of things are assumed to happen instantaneously (like gravity) so they don't have a speed per se. But in general relativity, everything has a speed -- and that speed is no greater than the speed of light.
GMD
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The example they provide is a good logical one. If the sun was removed from the solar system by some magical means, we wouldn't feel it (or see it) for another 8 minutes.
Yeah, that's the real trick. For those who aren't aware, getting gravity to "play nice" with both general relativity and quantum mechanics is pretty tough. Relativity models gravity is a warping of space. But coming up with a quantum theory of gravity is mighty difficult. There are theories that gravity acts through particles (the so-called gravitons you always hear about on ST:TNG) but I don't believe this has been proven yet.
GMD
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Well, actually that's not actually true, depending on how you define weak (the adjective). Gravity exerts the smallest force, but it does so over the greatest distances. OTOH, Electromagnetic forces are very powerful, but only over short distances. The nuclear strong and weak forces fall in the middle accordingly.
light does not have mass. you may be thinking of momentum, which it does have... general relativity says that the path of light (at least as far as the light is concerned) is not really bent, but space-time is bent toward massive objects. the light just follows the straightest path it can, but in a black hole space is curled up so much that the light ends up getting trapped. to just say gravity doesnt have mass so it cant be pulled into a black hole isn't enough. because after all neither does light! you could see that since the space which gravity acts on does not appear to be bent (as far as we can see) then perhaps its path depends on another property of space-time.
Photons are not particles in the sense of neutrons, electrons et. al which are massy particles.
Photons are better described as 'packets of energy'. Gravity doesn't just affect mass - it affects energy as well. Light doesnt get 'pulled into' a black hole, it just gets redshifted so much (by the gravity sucking the energy out of it), that its wavelength becomes infinite, and thus immeasureable.
Photons can exert a pressure though because they have MOMENTUM. Thus they have a 'mass equivalent', but they do not have mass, and that is not why they cannot escape black holes.
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If I am not mistaken, nuclear weak force is fairly rare, compared to the others. I always thought nuclear strong was the strongest, electromagnetic 2nd, then weak, then gravity. "Gravity is not a force, it is a product of space and time" I love physics, and am considering doing physics in college.
Actually, the distance dependance of gravity and electromagnatism is identical - inverse square. (Twice the distance a quarter the force.)
The reason that you don't have electromagnatism influincing planets is that once you get to about 1e-8 m, you are likely to cancel out your positive charges with a negative charge nearby. Gravity doesn't have that problem (no such thing as negative mass).
So it's not the distance, it's the matter which is between here and there.
Gravity distorts time. Hell, if you took gravity out of the equation instants would run together and all things which define time would go away- gravity causes time. [Okay, obvious problems with using the word "cause" here, but suffices to say that without gravity, you don't get time, got it?]
As you approach the speed of light, time is also distorted. At exactlty the speed of light, time for you is essentially brought to a halt.
What we're really looking at in these cases isnt the speed of light/gravity, because those are "instantaneous" [in quotes because of all this talk of what defines time]. What we're really looking at here is the speed of the universe- the maximum divisibility of time.
So "Gravity moves at the speed of light", no shit. Anybody coulda told you that forever ago.
I dont have a physics degree, I just say things. Unintelligent ranting follows.
-- 'The' Lord and Master Bitman On High, Master Of All
What next? The speed of magnetism?
Yes, the speed of magnetism. The particle which mediates electromagnetic interactions is the photon which propagates at the speed of light. So if a magnet is suddenly given a push in one direction then there is a delay before distant particles notice a change in the field of that magnet.
This is an analogous result for gravity and the postulated graviton particles.
It's one thing to not understand something, we all have our fields of expertise. But assuming you know everything based on some limited high schooling makes you the saddest kind of idiot.
:wq
"In general relativity, one learns that any "information" cannot travel faster than light"
What about quantum pairs? Move them apart, and a change in one is reflected intantly in the other.
That's why I specifically said "In general relativity...". Quantum pairs are from the theory of quantum mechanics, not general relativity. Physicists have been working hard to try to combine relativity and quantum into a single unified theory. However, problems arise when the two theories predict different things -- such as the quantum pairs example you listed. According to relativity, there would be a finite time lag for the change to be reflected in the second entity of the pair whereas quantum would say that the change is instantaneous.
Incidently, I heard that a few years ago an experiment was performed on quantum pairs and, sure enough, the change was indeed instantaneous. Can anyone else corroborate this?
GMD
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Relativistic speeds are usually measured in terms of gamma, not meters per second. Gamma is a value that represents the amount of time dilation and mass increase an object has; if you're moving at 86% of the speed of light (~206257211 m/s) then gamma is ~2.0, meaning that time would run twice as fast for you, and to a relatively stationary observer, your mass would be double what it is at rest. Gamma is calculated thusly:
y = 1 / sqrt(1 - (v^2 / c^2))
Gamma can rise unbounded; as your velocity approaches light, gamma rises exponentially, reaching infinity when your velocity is equal to that of light. I'm assuming that the original paper used values of gamma for measurement, rather than meters per second.
More about gamma here.
"Destroy science and religion. Science would re-emerge exactly the same; but not religion." - Penn Jillette, paraphrased
Okay, I'll bite.
A photon delivers an impulse when it is fired or when it is destroyed on impact with matter - but when it is in transit in space it has no mass.
Imagine a giant cluster of light, like fired by a superlarge pulse laser. It will transfer momentum to whatever it hits, but it does not actually have mass, so when its in transit this massive ball of light will not suck in anything with its gravity.
- Strong
- Electromagnetic
- Weak
- Gravitational
I even fetched a URL on a whim, just in case you disagree for some reason.How about this: a photon has zero rest mass. However, it is never at rest, but travelling at C. It does have energy, which translates to a very little mass and does warp space time, but when it hits something, that energy goes away, and so does the photon.
I wonder if a sufficient density of photons would collapse into a black hole.
"We returned the General to El Salvador, or maybe Guatemala, it's difficult to tell from 10,000 feet"
It's accomplished via huge (4 ft. diameter, 2.5 mi. length) tubes in an L-shape. A laser is then bounced along the length of the tube, and measures its distance very accurately: to within 10^-16 (!) cm, or about one hundred millionth the diameter of a hydrogen atom. Any change in the distance is a possible indication of a gravity wave passing through from some distant, powerful source. The fact that gravity decreases exponentially with distance means that even gravitational waves from extremely powerful sources, like binary neutron-star systems, are very weak when they get to Earth.
Of course, other vibrations can screw this up, so these observatories are really isolated (both geographically and mechanically) and data is compared from around the world. Lots of information is available at the LIGO (Laser Interferometer Gravitational-Wave Observatory) website, where I got most of the specs listed here.
That's it. I'm no longer part of Team Sanity.
While we think of mass and momentum being related by speed, energy and momentum are related by FREQUENCY.
Here's some equations if you want to wrap your head around them: equations
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the slightly longer answer is "because in the sun's inertial reference frame (i am going to leave gen.rel out of this) the sun still has the same mass."
if you don't understand what I just said, read more about special relativity, kay?
My life in the land of the rising sun.
Actually if I'm not mistaken, gravity and electromagnetic both exert a 1/r potential (1/r^2 force). So their distance range is the same.
So at short distances:
strong>weak>=electromagnetic>gravitationa l
but this isn't quite right because the strong force has two characteristics, a main force and a residual force. The main force is what keep quarks together in neutrons and protons. That's absurdly strong, and it's strength actually INCREASES with distance. However, the residual strong force is what keeps the nucleons together, and falls off really fast with distance, like the weak force.
At long distances things are a bit simpler:
Electromagnetic>Gravitational>strong>weak
The problem with this is that the electromagnetic and gravitational are relative. You can't go by the constants associated with the field, because they're defined by us (for example, what if mass were in terms of petagrams? Then G~10^19, and the force (in terms of petanewtons, I think) would skyrocket.)
Point is that it's all dependent upon the system you're talking about and the units you're talking about them in. We really can't compare them.
The best way to predict the future is to invent it.
http://www.what-is-the-speed-of-light.com/roemer-s peed-of-light.html
burris
To perform the experiment, numerous (probably several thousand) measurements are taken, but due to imprecision in the process of taking the measurements (imperfect measuring equipment, human error, etc) you get a variety of results. These answers could vary from well below c to well above it. If Einstein was right and nothing propogates faster than c, the higher results could only be attributed to imprecise measuremements, but you can't throw those measurements out if you are trying to be objective.
At the end of the process, you have something vaguely resembling a normal bell curve, where the height of the curve at a point along the x axis (velocity) is a measurement of the relative frequency with which that speed of gravity was obtained as a measurement. The total area under the curve will be exactly 1. In many cases, the curve may not be symmetric, but for an experiment such as this, you are unlikely to obtain an assymetric curve (Central limit theorem of statistics, or some such thing). A line right down the middle of the curve shows the measured average result (.95c).
A confidence interval is then picked (it is a shame that this interval is not mentioned in the article, but it is almost assuredly at least 95%, probably even 99%, or 99.9%). This percentage is converted to decimal (95%=.95, 99%=.99, etc), and a symmetric region around the average score with that area is blocked off. This blocked off area has a minimum X component of .7125c, and a maximum X component of 1.1875c, the difference between each of these and the average measured velocity being .2375c, which is 25% of .95c.
And that's where the 25% margin of error comes from -- for their desired level of confidence, the variance in measured results was off by no more than 25% of the value that was actually obtained as the mean.
Since the value of 'c' lies WELL within the bounds of the margin of error of the experiment, and pre-existing theories support the speed of gravity being c, this experiment supports those theories. It is important to note that this experiment did not prove anything, it only failed to disprove that the speed of gravity is anything other than something very close to c.
File under 'M' for 'Manic ranting'
the weak force is what hold sub particles together or soemthing like that. strong holds the nucleus of an atom together, electro-magnetic holds an electron to an atom, gravity IS a force and it has very very very little effect on the atomic level.
I am the Alpha and the Omega-3
Well, except that in the initial design, at least, they used an intermediate stage to transfer the momentum from the radiation pressure (generated by a conventional fission bomb)...they use the radiation to ablate the outer surface of a cylinder of U-238 (natural uranium) surrounding the deuturium/tritium to use the uranium to compress it, which also trips an initiator placed with some U-235 centered in the center of the deuturium, causing it to fission, which creates two massive pressure waves, an incoming and outgoing, that compresses the deuturium mightily. This ignites fusion in it, which, in turn, releases enough fast neutrons to ignite fission in the normally unfissionable U-238 that surrounds it. The fissioning of U-238 actually produces most of the yield of this device, "Mike", which was about a megaton. Quite an intricate piece of work, really.
Now, what did this have to do with this discussion again? Oh, yeah, the momentum of photons. I guess it's marginally ontopic. (Please forgive me, I just finished reading about the development of the H-bomb and couldn't keep from showing off the neato stuff I just learned.)
Anywways, that's more or less how my high school science teacher explained it.
File under 'M' for 'Manic ranting'
- the inverse square law implies that the ratio of these forces should remain constant with distance, but
- everyday experience and astronomical evidence seems to suggest that gravity grows stronger than the EM force at macroscopic scales
I think the key to resolving this conundrum is to realize that the EM attraction is proportional to the relative charge difference between two bodies.- At microscopic scales, one is often dealing with individual EM charges, so the relative charge difference at that scale is large and the force is strong.
- In macroscopic objects, it is difficult to separate macroscopic amounts of charge precisely because the EM force is quite strong, so macroscopic objects usually have relatively small charge differences and the macroscopic EM force seems relatively weak.
Compare this to gravity, which only has one type of charge--mass--which always increases as the size of the object increases."It take 9 months to bear a child, no matter how many women you assign to the job."
Strange, 20 years ago I was taught other people had experimental evidence agreeing with a prediction that the effects of gravity move at light speed:
In 1882 Simon Newcomb observed an excessive perturbation in precession of the orbit of mercury, to the tune of 43 seconds of arc per century. In 1915, Albert Einstein showed this could be explained by the propogation of gravitic wave effects at the speed of light...
But thanks for playing.....
And if you remember relativity, when an object is travelling near the speed of light, the mass increases. So the theory at least makes sense. Here's another thing to ponder. If an object the size of the sun suddenly acquired the 99x its mass, would it not either collapse upon itself, or expand rapidly, nova, and the core would collapse upon itself, causing the same result, a singularity, with a small event horizon. And it will be this singularity that will collide with Earth, ripping through it in a fraction of a second, and the sudden, combined gravitational effect on earth will cause it to very suddenly pull out of it's orbit toward the origninal center of gravity of the sun, with a nice city sized hole carved through it.
point of note: a "nova" is what happens when fresh yummy hydrogen falls on a white dwarf. Boom! A "supernova" is what you were talking about. Confusing the two is a little dangerous, because they're two completely different processes.
Depends on the mechanism of acceleration, really. If it's merely "moving" at a Lorentz factor of 100, then no, of course not, because all you did was Lorentz boost the system, which you can always do. In the Sun's rest frame, it's fine still, of course. In the boosted frame, it's also incredibly flattened (like a pancake - by a factor of 100, no less) but amazingly enough, you can still work out hydrostatic equilibrium for it, and determine that yes, it is still in equilibrium, and not going to blow up. Beauty of relativity - laws of physics are Lorentz boost invariant.
However, if you're actually accelerating the thing, now that's a different story. You (still) won't make it go supernova, because you're NOT actually increasing the number of particles inside it, and that's what breaks hydrostatic equilibrium - pressure generated versus gravity, and BOTH of those change in the boosted frame - but you WILL screw it up really badly by sending pressure bubbles through the whole thing. Since the Sun isn't a rigid body, you'll probably strip the chromosphere right off of it, and leave the core bare. This, however, won't due much except really really confuse distant astronomers.
Gravity is a long-distance force that decreases as inverse distance squared. This is Newton's famous 1/r^2 law, and it remains unaltered by the theory of general relativity (after all, Newton's laws are just a limiting case of General Relativity.)
With a short-range gravitational force, decaying exponentially with distance, stable planetary orbits and galaxies, with their literally astronomical extent, could not exist.
To increase the sensitivity ESA is building a flotilla of space craft that together form a network to measure gravitional waves.
The mission is called LISA and will be supported by a pre-cursor mission SMART-2 to develop the necessary measuring and flotilla operations.
Read this FAQ.
The weak force doesn't actually hold anything together.
The strong force holds the quarks in the nucleons together, and this also holds the nucleus together - as the nucleons get close to each other, they're able to "see" the quarks inside each other, and are attracted. The strong force is actually infinite range, but appears to be a limited range because quarks are always bound into colourless states, and the strong force works on colour charge.
The weak force mediates between various particle decays etc, the most well known of which is beta decay, where a neutron turns into a proton, electron (and an electron neutrino).
Gravity is itself the warping of space. The best way to explain is by imagining a 2 dimensional world instead of a 3 dimensional world (spacial dimensions). Imagine a 2-D surface like the top of a soft bed. Objects on the bed that are 3D are simply 2D objects with mass (gravity field). Place a bowling ball in the middle of the bed, and it will warp the surface of the bed into another 3rd dimension (down = force of gravity in this universe). Anything nearby that bowling ball on the bed will be drawn towards the bowling ball (gravity in 2D) if it is nearby. Assume you were to roll a ball in a straight line across the bed, and it came across the pit in the bed made by the bowling ball... the ball's path would curve due to being near the bowling ball... this is what happens to light usually near gravity. Light bends, but it THINKS it's going in a straight line b/c it is space itself that is curved (bed's surface). Imagine a ball travelling in a circle around the bowling ball within the pit formed by the bowling ball on the bed. If it's located at a very specific point, travelling with enough speed, the ball will remain spinning in a circle around the bowling ball forever (assuming no friction). This is how planets stay in orbit and how light can become trapped at the event horizon of a black hole. Many things that are closer or not traveling at the correct speed and direction will be sucked in.
Take this analogy and think about it in our 3D world, and you'll see that gravity is another dimension in which space itself is warped. The "speed" of the warping of space is simply how quickly a change in gravity would affect objects and light nearby. Theoretically, the only known way to shift gravity is to shift the mass of an object, and since matter and energy are restricted to the speed of light, gravity should also be limited to the speed of light. Also, the warping of light from an outside source by jupiter's mass (gravity), should not instantaneously warp the light, but warp it at the speed of light as well.
In case anyone is interested, you can find an abstract link to the original paper that predicts the quasar deflection caused the Sept 8th close approach, here. The paper was published in the Astrophysical Journal in 2001 by S. M. Kopeikin. Interestingly, this theory paper has listed only two citations but the citation rate is sure to climb now that the observations have been made.
Flintstones (Hanna Barbera): Sep 30 1960 (ABC)
Road-runner (Warner Bros.): 1949
The fact that gravity decreases exponentially with distance
They decrease with the square of the distance, not exponentially.
very weak when they get to Earth.
LIGO is hoping to detect gravity waves at a range of over 3000 light years. Even at that range the energy is 300 MILLION WATTS PER SQUARE METER. (About 28 million watts per square foot.)
So while the measurable effects are tiny the energy is enormous.
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- - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
I wouldn't take their word for it.
This paper gives a good case for gravity traveling faster than light and I'm pretty sure all the working Newtonian gravity calculations assume instantaneous gravity:
"Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target"
OddManIn: A Game of guns and game theory.
There was another poster that also claimed this would have been due to the air heating up near the gong.
However, this professor continued his demonstration with sooting the gong heavily (taking it from polished to near-black), and then firing the flash again. The sound was significantly softer, noticable by all attendees (around 120), and he explained this by the photon package having been absorbed instead of bouncing (the gong only got half the impulse from before).
In a scenario where heat was the cause of the sound, sooting the gong would have caused a significantly louder sound as the light was absorbed, instead of (as happened) as softer one.
For instance, it assumes that electrons are point-particles with no mass, yet have a charge in many equations. This is impossible. The electron is known to have mass, and the best model for electrons is a donut-shaped spinning ring. This accounts for it's moment, spin (up or down), charge, etc. and it's the most accurate model for predicting electron shells in atoms. Quanta (packets) are just ways to approximate and estimate energy and matter, yet they are about as accurate as assuming a horse is a sphere for mathematical simplicity... lol.
Gravitons are a ficticious creation to try to quantize gravity distortions in space-time. They essentially said "hey, this works with light, so let's try gravity" and it doesn't add up. In order for gravitons to exist, you'd have to have these particles with no mass jumping from every object in the universe to every other object in the universe at infinite speed, yet not accumulating on any object for long enough to crush it, just to put pressure on it and keep it in place. There's no explanation in the world of quantum mechanics that fits gravitons with known reality. Even light "particles" can't travel faster than the speed of light, and now that gravity has been measured to be about or equal to the speed of light as well, gravitons are lookin' like a even less of a possibility of being reality.
Another major flaw of quantum mechanics is the belief that something can exist in multiple states at once or even many PLACES at once! Simply because the MATH says that there is a probability of a particle being in a certain state or position, does not mean that it is or isn't in that state. Quantum Physicists routinely treat unknowns as being in a state of flux until measured, when in reality they are either one or the other... you just don't know until they check. I actually heard physicists saying things such as "the moon isn't really there until you look at it" and garbage like that. Let's say you have a truly random function that pics a number between 0 and 1, a quantum physicist would tell you that the output is essentially every possible number between 0 and 1 at the same time until you look at the answer. They believe simply because the probability of something can be expressed as a wave function, that the object IS a wave, therefore it exists in all possible states at once. This is beyond illogical to stupidity... and though they claim to have created small quantum computers which work on the logic of 0, 1, and some state which includes both 0 and 1, they also say that "there is no way to decode the information at this point... just to compute it... theoretically". In other words, they did the math and think the darned thing is working how they thought it should, but have no real way to check it.
In order to buy into this stuff, you have to believe in alternate universes, many multiple dimensions, and that all matter and energy exist as waves. (vibrating strings in string theory). While I believe the math is useful for many purposes, it is akin to how astronomers once placed earth in the center of the solar system and devised many circular tracks for the sun, moon, and other planets to revolve around the earth in a manner which matched what was observable in the sky. The math works in a lot of situations to determine outcomes, but analyzing the math to determine the structure of the universe and creating imaginary particles is beyond theoretical physics and into plain old science fiction and fantasy. I think we're in for another paradigm shift away from quantum physics in the next 20-50 years. Most physics professors I know think gravitons are fictitious & think string theory is just about to give itself enough rope to hang itself. lol. lata
There is no strong force. It's a myth. Just like Neutrons are a myth. No, I'm not joking. Anytime you extract a neutron from an atom, it breaks into a proton and an electron (hydrogen). A Neutron is not a true particle, it's simply a compressed proton and electron.
First of all, you're still going to have an interesting time explaining how all of those nice, positively-charged protons are bound into an incredibly tiny space without the strong force holding them together.
Secondly, the production and decay of neutrons is mediated by the weak force, not the strong force.
Thirdly, your model fails to explain mesons and the zoo of other particles that can be produced even in relatively low-energy accelerators, while the quark model explains it nicely.
Protons become neutrons when an electron and an "up" quark interact to produce a "down" quark and an electron neutrino. The inverse process - decay of neutrons into protons and electrons - happens when a "down" quark decays into an "up" quark, emitting an electron antineutrino and an electron.
The neutrino emitted during the decay has significant momentum. Its existence can be shown - and was originally inferred - by tracking the charged particles emitted when a neutron decays into a proton and an electron. In many cases, both of the charged particles are going in the same direction. To conserve momentum, something else had to be fired off in the opposite direction during the decay. That "something" is the neutrino. If a neutron was a bound proton/electron pair, there would be no third particle to explain the momentum discrepancy.
You're also overlooking the fact that a bound system has less energy than an unbound one. Which would mean that in your proposed scenario, _neutrons_ should be the stable nucleon, which is at odds with observations.
Or, you may have written that post as sarcasm. Either way, moderators have been falling for it.
The rest of your post is even sillier, so I'm not going to bother with it.
In summary, your proposed model is demonstrably incorrect.