Can any of you physical science types summarize the latest theories of gravity in general scientific layman’s terms? The last I saw, they were still searching for the Graviton, the Graviphoton and the Graviscalar particles to explain gravity. Now I’ve heard that’s all been thrown out the window (or into the singularity, if you prefer), but I’m not quite clear on what theory is replacing it.
thanks,
** Jumping onboard**
I have a real interest in this as well. Seems like everything i have read about gravity being a constand contradicts with it’s practical application in stellar mechanics.
If you grant that all matter that exists in the universe has ** always **existed then dosen’t all matter interact gravitically<SP>?
I’m phrasing this badly so I’ll rephrase badly and hope someone else can interpet.
You can create light from lightlessness. But matter is just there exerting gravity which travels as a wave but since it has ALWAYS existed then dosen’t it’s effect (admittedly miniscule at any distance relating to it’s overall mass) act instantaneously?
Another rephrasing is:
You are one light year from my location. I shine my patented Pak flashlight-laser at you and it takes a year for you to see it (unless you got bored waiting for me to turn it on. But lets supose we are both standing on some big stationary asteroids at the same distance. Since both masses have always existed, does it take a year or less (since no wave is supposed to travel FTL) for the effect of me moving my rock to have an effect on your rock (granting that i could move the rock and also granting that you could detect it.)?
I don’t know if it is bad form to add to a thread so please forgive if it is.
humbly,
well, that’s what this inquiring mind wants to know! is gravity limited by the speed of light? is it still felt to be a wave/particle modulated phenomenon?
thanks for sharing! Hope we get more input/insight!
A scientist has recently put forth a novel explanation for the missing matter in our universe. The concept of mirror matter has been around for a while but a new application of gravitic theory has yielded an explanation for both missing matter and the existence of a parallel universe. String theory is also contributing to our understanding of gravity. However, the possibility of higher dimensions complicates the isolation of gravitic effects. Additionally, new questions about the existence of a cosmological constant further cloud the issue.
Happy reading!
Einstein’s General Theory of Relativity completely explains the results of all experiments and observations that have ever been made concerning gravity. The problem comes with experiments that have not yet been made: If you get matter hot enough, or dense enough, or otherwise in an extreme enough state, or look at it on a small enough scale, then GR and quantum mechanics ought to both apply, but the answers they give are not consistent. We can’t yet perform these experiments, and probably won’t be able to for a very long time, so we can’t say what the actual results will be, and thus, we don’t yet know which theory is correct in those situations. There have been many attempts at a Theory of Everything, or quantum gravity, the latest and most sucessful being String Theory, and this is where we end up talking about things like the graviton. It’s very probable that the correct theory will involve gravitons, and perhaps other particles like the graviphoton and the graviscalar, but we can’t say for sure.
Meanwhile, all theories and experiments (such as they are) agree that any information transmitted by gravity must be at exactly the speed of light. Yes, the gravity between two objects is always there, but changes are not always there. To look at an analogy, consider the surface of a pond: The water is always there, but when you toss a pebble in, the ripples only travel at a finite speed.
I believe the current thinking still involves gravitons, with the details of their properties being worked out. Gravity is still the red-headed stepchild of the four forces because it so weak that it’s hard to incorporate. Still, they’re making progress. IIRC one of the strong features of the superstring theories that many physicists are optimistic about is that they can incorporate gravitons.
Re: Gravity and the speed of light. That’s been discussed here a number of times and there are paradoxes. Gravitational effects do propagate FTL in a sense. Physicists assume an infinite speed of gravity in making orbital calculations, for example. However, it is reasonably certain that gravity waves move at the speed of light just like electromagnetic waves do. No one is certain, of course, since gravity waves have never been detected, but we’re not going to get around Einstein’s postulate that no signal travels FTL by superheterodyning a gravity wave.
Still, there is that infinite speed.
Gravity is a force caused by the bending of space-time. Think of space-time as a sheet of rubber and an object in space time as a marble. Now if we place the marble on the sheet of rubber, the sheet of rubber will bend. Now if we place another marble on the sheet of rubber the two marbles will bend the rubber and move towards each other. The more mass the marble has the greater the bending of the sheet of rubber and the stronger the force of attraction. Also the closer the two marbles are the greater the attraction. Now say we place a bowling ball on the sheet of rubber and a buch of marbles. The bowling ball will stay stationary due to its mass while all of the marbles will move towards the bowling ball. ie earth and all of the people. F = G (m1 m2) / r^2 where G is the universal gravitaional constant m1 and m2 are the mass and r is the distance between the objects.
I like to think of myself as smart, but I got about halfway down this thread, and my brains started leaking out my ears.
I thought that gravity was a force, much like magnetism. Do magnets emit fields or waveforms? I know light is made of particles(photons) but I had never really thought of magnets and gravity… hmmmm…
But that just illustrates the phenomenon, it does now say how it occurs. That’s what I’m looking for. Why should mass bend space-time? String theory does offer some clues as to why it should be so, as do the ideas of the fundamental particles of gravity. The links supplied above in the earlier post are quite helpful, but after 10 minutes of reading, my brain hurts. But its a GOOD pain!
Most people that I meet tend to think of gravity as a “force” like magnetism. Gravity works quite differently, in fact. The best analogy I can give you is the computer that is sitting in front of you right now. Why is it there? Why isn’t it falling towards the earth? The only reason that it is not, is because of the structural members that are accepting the mechanical load of it’s weight. The table is accepting stress that it distributes into the floor below it and the floor joists distribute that same load into the foundations of the building they are attached to.
Believe it or not, gravity is not the real cause of the loading forces in discussion. Gravity does not exert “force” upon objects. The forces in question here relate more closely to the work done of lifting your computer up onto your table. It got there somehow, right? The only way your computer got to its current position is through the work done by someone carrying it up into your house and placing it there. That is the real energy in question.
Gravity is really the tendency for objects to release the work done on them when given the opportunity to do so. It’s as simple as that. There is no attraction between the Earth and a falling body, merely the opportunity for the object to release the work done upon it to lift it out of the “gravity well” of Earth’s time-space curvature. All matter warps time space, but it takes relatively large objects like moons and planets to manifest this effect in a macroscopic fashion. The Cavendish experiments were among the first to demonstrate gravity on the micro scale of small objects. The method involved is well worth reading about. Enter “gravity theory” or “Cavendish experiments” at any search engine for some important reading.
Try to remember that falling objects are releasing kinetic energy (work) that has already been performed upon them. The computer crashing to the floor is merely releasing the effort of someone having lifted it there. There is no mysterious “force” involved. I hope that this has clarified what is so often a very cloudy issue.
This is my 995th post! One thousand, here I come.
Zenster, do you, by any chance, remember the definition of “work”? It’s force times distance, or more precisely, Int(F•ds). The fact that work is done implies that there is a force involved.
Tristan, the electromagnetic force is, indeed, mediated by particles, in essentially the same way that gravity is believed to be mediated by gravitons. in the case of electromagneticm, the mediator particle is none other than our old friend the photon, which is why light is electromagnetic radiation.
Quadgop the Mercotan, (and BTW, where is your name from?), there’s no complete answer yet to why mass bends spacetime-- M-theory (the decendant of sting theory) is the best we have so far. Einstein was able to say exactly to what degree and manner it does so, however.
pluto, physicists may approximate gravity as being instantaneous and Newtonian for most orbital calculations, but as long as you use Einstein’s theory, rather than Newton’s, you get the exactly correct answer assuming a speed of c. Of course, the math is easier a’ la’ Newton, and the difference is usually very small, so Newtonian gravity still gets used.
It is not up to science to say why something occurs. Science predicts what the result of an experiment will be based upon theory.
Asking why is the relm of philosophy or metaphysics.
But the universe is not infinitely old. We can only see/be affected by things that are 12-15 billion light years away (since the universe is 12-15 billion years old). And strickly speaking, your two asteroids would be even younger than that (the asteroids in our solar system are about 4 to 5 billion years old…of course that’s way more than enough time for light speed interaction between two asteriods in the same solar system).
Like Chronos was saying, gravity is everywhere but changes can be like ripples in a pond. In Einstein-ian terms, gravity may be the same thing as spacetime.
OK I’ve heard the forementioned Rubber sheet analogy (ie: think of space as a rubber sheet where heavier (denser) matter weighs down the sheet, thereby bending or warping it resulting in stronger gravitational attraction.)The problem I have with this concept is that the anaogy still depends on gravity to work. In other words, aren’t we using gravity (what else would make the sheet bend?) to explain itself?
I see where this analogy has merit when it comes to understanding a 3 dimentional, invisible concept in 2 dimentional terms, but it still doesn’t explain what the heck gravity IS, at least to my way of thinking.
I’ve been reading these posts with great interest. Nice to know that such a basic question can still generate a lot of debate and feedback.
The asteroids may be younger than the actual age of the universe, but they matter of which they consist shouldn’t be.
Perhaps my phrasing was muddy. All the atoms they are made up of are original monoblock matter.
That was good. Just an observation. I majored in physics and heard a lot of explanations told different ways, but this has to be one of the best I’ve heard. I have got to remember this one.
Chronos, when you say, “The fact that work is done implies that there is a force involved.”, are you referring to “work” being done by mediating “gravitons”? Being not quite up to date on string theory, I still perceive the “work done” that allows a body to fall into a gravity well as the work performed to originally lift it out of that same well (or another). The “lifting work” released by a “falling” object manifests in the form of kinetic transfer to the attracting body (ergo conservation of energy). This is regardless of whether that work is expressed through direct impact or orbital perturbation. I do not see the need to express an object’s descent into a gravity well as being an example of “work done”, but instead as “work released”.
Please provide a link to any theories that elucidate how “gravitons” couple (to) masses and “mediate” their mutual attraction. I think that it would help myself (and others) to better understand your statement. Lastly, just to stir the pot, are “gravity waves” quantal in nature?
Try to remember that the rubber sheet analogy is a two dimensional (the third dimension of depth, in this case, is representing the “strength” of the gravity well and not a strictly spatial parameter) representation of a three dimensional system. All three spatial dimensions (height, width and length or X, Y and Z) have been integrated into the two dimensional rubber sheet.
It is difficult for the human mind to visualize what the three dimensional model would look like, which is why the rubber sheet analogy is so popular (and functional). “Gravity” is not warping the rubber sheet in the analogy. Instead, the effect that you are attributing to gravity, is in fact the warping of space time by matter itself.
here is the explanation for gravity. The universe is expanding at an accelerating rate. Distant galaxies are becoming ever more distant. The more distant they are, the faster they are receding, but the lower their acceleration. When we look at a galaxy a long distance away, we are viewing the universe as it was in the distant past. In the distant past things were moving apart at a steady rate–the speed of light–with no acceleration (you can’t go faster than light). As time passed, the rate of relative movement decreased, but the acceleration increased (my personal theory to explain this is that energy is constantly being congealed into matter, but leave that to one side for the moment, it’s not important). At the present moment, the acceleration of the expansion of the universe is 32.2 feet per second squared–the acceleration we perceive as gravity.
You haven’t read about this before because virtually all calculations on the expansion of the universe assume that the entire universe is expanding at a rate of “about 65 kilometers per second per megaparsec. Converting that to meters and seconds, we have about 2*10-21 meters per second per meter. In other words, if your finger were a meter from your nose, and expanding away at the Hubble rate, then it’d only be moving at .000000000000000000002 meters per second.” as written by Chronos in these very pages back in Jan 2000. But since January, we’ve discovered that the expansion is accelerating and presumably is at a greater rate the nearer you come to the observer (me). So basically, everything is getting much, much bigger at a really alarming rate, which is itself increasing at and even more alarming rate. Why don’t we notice it? Because everything is expanding uniformly. The sun is bigger, the earth is bigger, the moon is bigger, and we are bigger.
This implies that the speed of light is also increasing (otherwise, measurements involving light would give away the expansion). At the far reaches of the universe, light is very, very slow. Beyond a certain point (call it the singularity for want of a better word), light stops entirely. And what happens when energy stops? Bingo! It becomes matter. Dark matter.
gabby, most of what you wrote was right on, but you lost it when you started claiming that everything is getting larger. The Universe is getting bigger, but the matter it contains is staying the same size. You see, gravity counteracts the expansion force. Where there is matter, there is gravity. Where there is gravity, there is little or no expansion. Where there is mucho gravity, there is contraction (a black hole).
The universe is expanding, but mostly in (nearly) empty intergalactic space where gravity is practically non-existant. (I say nearly because space is never totally empty. There are always a few stray particles floating about.) As empty space comes into being, the galaxies get further apart.
I can’t imagine how the speed of light in a vacuum could ever change.