"Gravity is a weak force, in the sense that the gravitational force between two protons is about 10^33 times weaker than the electric force between them. And I'm using protons rather than electrons here to make the gravity stronger - with electrons gravity would be almost 10^40 times weaker.
This has various consequences, but one is that gravitational waves are absorbed by matter much less than electromagnetic waves. It would be fun to estimate the amount of energy absorbed by the Earth as this particular gravitational wave came through, but it would be absurdly small. Gravitational waves make neutrinos look like rampaging gorillas."
Rephrasing, and assuming waving commutes with rampaging, gravitons make neutrinos look like WAVES of rampaging gorillas. I'm no physicist but to answer the original question I'd hazard a guess: quite far!
Imho whatever is carrying gravity between masses cannot itself have a mass.
I can't think of an obvious reason the Higgs mechanism wouldn't work for gravitons, but I could be mistaken, it's not exactly the most intuitive area of physics.
Also, keep in mind that the strong force transmits the force between colour charges while also having a colour charge itself, so it isn't entirely inconceivable for the force transmitting the attraction between masses to have a mass.
No clue if a massive graviton would allow for black holes, but it's not entirely sure what black holes even are (especially quantum mechanically). At the very least it's presumably possible for some particles to escape it (e.g. as Hawking radiation).
(1) We should see this as some inconsistency in how gravity scales with the mass of a black hole. The larger ones would have proportionately greater 'drag' on leaving gravitrons, pulling more in.
(2) If they are massive, and therefore subject to slowing, shouldn't gravity waves leaving a black hole be subject to some sort of doppler effect? Should we be looking for red/blueshifts in these waves?
(3) If gravitrons have mass and are subject to gravity, what brings that gravity? What sub-gravitron particle regulates gravity going in/to/out of the gravitron? This would require a new set of particles be created by non-gravitron massive objects (ie black holes) alongside the gravitrons. Like I said, too strange to exist.
> If the massive gravitron was leaving a black hole it would be slowed by the black hole's gravity.
A graviton wouldn't be able to escape a black hole. A photon can't, and it's massless. The gravity of a black hole is actually a self-sustaining effect of the curvature of the spacetime around the black hole.
> (1) We should see this as some inconsistency in how gravity scales with the mass of a black hole. The larger ones would have proportionately greater 'drag' on leaving gravitrons.
We don't know details of the gravitational field around black holes and the mass that created it, because none have been observed close up. To an extent, the mass of a black hole is defined by its gravity.
> (2) If they are massive, and therefore subject to slowing, shouldn't gravity waves leaving a black hole be subject to some sort of doppler effect? Should we be looking for red/blueshifts in these waves?
Again, photons are massless and subject to the doppler effect. Gravitons, massless or not, will be too.
> (3) If gravitrons have mass and are subject to gravity, what brings that gravity? What sub-gravitron particle regulates gravity going in/to/out of the gravitron? This would require a new set of particles be created by non-gravitron massive objects (ie black holes) alongside the gravitrons. Like I said, too strange to exist.
Force carying particles can interact with themselves, c.f. gluons in QCD. In fact, GR is a non-linear theory so there will be non-linear interactions (as far as you can describe them in the weak limit).
But isn't the curvature of spacetime around the black hole supposed to be the effect of its interaction with the graviton??
Is this where the translation from GR -> QM breaks down?
Sort of, to get a graviton you introduce perturbations on a background metric. (Basically small wiggles of spacetime around an 'average.') You don't do anything like that when you solve the Einstein equations. Consequently, the background spacetime ( that is, the black hole) is not really made of gravitons. (At least in some sense.)
This inconsistency is a part of general relativity (even though gravitons themselves aren't). A black hole does not follow the GM/r^2 gravity law.
> If they are massive, and therefore subject to slowing, shouldn't gravity waves leaving a black hole be subject to some sort of doppler effect? Should we be looking for red/blueshifts in these waves?
Yes, there is a doppler effect.
> If gravitrons have mass and are subject to gravity, what brings that gravity? What sub-gravitron particle regulates gravity going in/to/out of the gravitron? This would require a new set of particles be created by non-gravitron massive objects (ie black holes) alongside the gravitrons. Like I said, too strange to exist.
Gravitons. Every now and then a pair of gravitons may exchange more gravitons (these are also virtual particles, so it's fine). This is why Feynman diagrams exist, so that you can not only calculate the interaction between two particles through a graviton, but also calculate the contribution of the lower-probability situations where more gravitons magically appear to transmit gravity between gravitons.
This is nothing new. Gluons (the carrier for the color/strong force) do basically the same thing. They are also bound by the force they carry, and thus gluons can interact with each other with more gluons.
Because these are virtual particles and only exist as a probability, this doesn't lead to infinite recursion. The secondary gravitons are improbable, and the tertiary gravitons more so, and so on, and the final series converges.
Or not, and we yell "look behind you!" and then dump the infinities out the window.
When I first learned about renormalization formally (i.e., with equations) I realized it wasn't that bad. But still, pretty sneaky :P
Perhaps, no clue how a quantum mechanical gravity would interact with a black hole.
>(2) If they are massive, and therefore subject to slowing, shouldn't gravity waves leaving a black hole be subject to some sort of doppler effect? Should we be looking for red/blueshifts in these waves?
The Doppler effect happens even for light, which isn't massive at all (that we know of).
>(3) If gravitrons have mass and are subject to gravity, what brings that gravity? What sub-gravitron particle regulates gravity going in/to/out of the gravitron?
There's no reason they couldn't interact with themselves, in fact I guess that's probably the most likely case.
The particles leave the event in a smooth wave. Then they run into other waves, or each other, or just the background gravity fields. This perturbation should cause them to clump together. So in short order the smooth wave would become large blobs of gravitrons more akin to raindrops than waves. And without anything holding them apart, might not some of these clumps condense into some sort of ... I don't have the words for such an object. I wouldn't want to get in its way.
(i.e., anti-gravitons and gravitons are the same thing, just as anti-photons and photons are the same thing).
There are a variety of other theories of gravitation with gravitons, but as far as I know, there are none in which gravitons are not their own antiparticles. (There may be such theories available in universes with a very different cosmological constant or with different numbers of dimensions than the one we are in).
I like the idea of anti-gravitons being the inside of a graviton, or inside of a black hole. Given the inside of a black hole is essentially the end of time, coming out of a black hole or coming out of an anti-graviton, could equal going back to the beginning of time.
Massless particles don't have energy. Massless and energyless particles have no speed. I have no interest in massless and energyless particles that stand still.
Because if so, and assuming you have some reason for believing this i.e. you can prove it, I would urge you to forward these findings to a physics journal of your choice posthaste, as this basically represents a total refutation of much of physics of the last century or so. You will easily win a Nobel Prize.
Forget gravitons, this already exists in pure general relativity. Spacetime is curved around a massive object, and that curvature contains energy. That's just another word for mass, so the curvature itself exerts gravity. This creates more curvature (...etc etc). This is one of the reasons as to why Einstein's equations are nonlinear.
Note that the concept of having mass is separate from the gravity force. Interaction with the Higgs field gives rise to mass, whereas gravitons are the force carrying particle for gravity.
All massive particles get their mass from the Higgs field.
IIRC we do know where protons get their mass. The internal color field has some energy, thus some mass, which comes from that field interacting with Higgs.
* http://physics.stackexchange.com/questions/64232/your-mass-i... * https://en.wikipedia.org/wiki/Proton#Quarks_and_the_mass_of_...
By the way, this is why the strong nuclear force has such a short range. Gravity has infinite range as far as we can tell, so that makes it unlikely that the graviton, if it exists, has mass.
If your 1 billion light years from earth, you are still effected by the Earth's gravity (well its likely smaller then experimental error but never mind that it still exist).
So there needs to be gravitons from Earth flooding the entire sphere of space for 1 billion light years around the Earth. All these gravitons have mass, and are emitting their own gravitons. Which all have mass and energy! Where is this mass and energy coming from? It really can't, it violates the laws of thermodynamics. But so does Dark Energy so who knows.
Photons don't have mass. If they had mass they couldn't travel at the speed of light.
Suppose you have two quarks and you start to pull them apart. The gluons that transmit the force between the two quarks tend to "bunch" together because they have their own charge. You can think of it roughly like a rope of gluons trying to pull the quarks back together.
If you keep pulling on the quarks, you might expect the gluons to eventually "break". But this doesn't happen, because the gluons act on each other. If there were ever a break, more gluons would join in, tugging the break back together. Eventually, you end up with so much energy density in all these gluons that they start forming new quarks and other particles. These new particles will bind with your quarks and each other to form color-neutral particles.
So I spoke a little imprecisely. Gluons, being massless, have infinite range. But you won't ever see the strong force acting over any large distance because anytime you try to get color-charged particles far enough apart, you'll end up making more particles.
Wikipedia has a brief write-up that provides an illustration. https://en.wikipedia.org/wiki/Color_confinement
Best example: the Hydrogen atom is supposedly quantum, but if it is quantum, where are the photons? the q^2/r potential is a mean field that one finds from classical electrodynamics, it isn't formed by the summation of photons. [Another mental poker, photons are momentum eigenstates, so how can potential be described in position space? You'd need to sum up an infinite number of them! (For EM students, recall how to represent 1/r in spherical harmonics or in terms of sines and cosines)]
What happens, as I understand it, is with strong fields, one tends to use a semi-classical description because in the strong field limit, one deals with many photons, which should approach the classical limit.
Basically, quanta are like "pertubations" of the fields from their "free" solutions, as they are in GR (linearization of the GR field eqns) and as they are in EM. Free essentially means in the absence of sources, like charges, or masses for GR. So trying to explain general phenomena in terms of "pertubations", which are basically the solutions for "free" fields, is not always fair.
One doesn't always face this in high energy physics because in HEP, most of the incoming and outgoing states in a problem are these "free" solutions. For example when doing scattering off a hydrogen atom, the incoming states are "free" (a free nuclei, a free electron), so one can use photons for that phenomena, and one finds that the scattering is like scattering against a (mean) 1/r potential.
But in the case where the strong fields don't turn off, like when you are bound to a Hydrogen atom, or when considering nucleons in nuclei in the low energy limit, one turns away from the pertubative, photon/gluon model and either solving the problem numerically or treats the fields as semi-classical, as with the Hydrogen atom. For my field of laser-plasma physics, this shows up in the so-called "Volker-state", rather than treating the strong laser field as a sum of innumerable (ie., not-simulatable) photons, one treats the Laser field as a semi-classical background for the quantum guys (electrons, ions).
I think lensing is like strong static fields in EM. One wouldn't really think of them in terms of quanta of the field.
Surely we create gravitons whenever we move a mass just like we create photons whenever we move a body that interacts electromagnetically? Isn't the point that we're constantly exchanging gravitons with all matter as they mediate gravitational attraction.
And maybe real hover boards
Maybe we could make orbital graviton beam generator that could literally suck an object off the face of the Earth.
Inside a charged black hole there is a second horizon. Beyond this point the black hole is gravitationally repulsive. http://casa.colorado.edu/~ajsh/rn.html
> The Universe at large appears to be electrically neutral, or close to it. Thus real black holes are unlikely to be charged. If a black hole did somehow become charged, it would quickly neutralize itself by accreting charge of the opposite sign.
> It is not clear how a gravitationally repulsive, negative-mass singularity could form.
So it falls under the same sort of category as negative- or imaginary-mass 'exotic matter': not ruled out, but there's nothing suggesting that it actually exists.
I vaguely recall other weird edge cases where gravity is repulsive, but I can't find any links right now.
This is an interesting concept. As far as I'm aware, we have ways of measuring weight, but no way of measuring mass. How would you know whether something weighed more than it "should", based on its "mass"?
I have no intuition for this. Maybe it's valid, but your other two examples raise grave doubts about this one.
> Or you throw it at something of known mass and measure the speed it imparts onto the known object.
Blind application of the principle of conservation of momentum does indeed tell us that we can measure the mass of one object by colliding it at known velocity with another object of known mass and measuring the resulting velocities. But I tend to worry that the mechanism for transferring velocity from one object to another object in a collision is the force it exerts during the collision, and that that force might be determined by the object's weight (also a force) rather than mass (a platonic concept). But, I'm not sure here either.
This ties in to the "fun factoid" that physics has no explanation for inertial mass and gravitational mass being the same quantity. If they in fact aren't necessarily the same thing, momentum transfer, measuring inertial mass, would solve this problem. If there is a reason they coincide, this approach will be confounded by that reason.
> Or you hang the a known mass and the unknown mass on strings and measure the force of gravity between them
I'm absolutely certain this wouldn't work to distinguish the mass and weight of an object that has extra weight because it's emitting extra gravity. The measured force of gravity is going to include the extra gravity you're trying to ignore.
Then we are speaking of different things. I understand 'weight' as how heavy something is within particular gravity field (ie on a bathroom scale on earth) whereas mass is independent of local gravity. The schemes I suggest measure mass without resort to weight.
>>I have no intuition for this. Maybe it's valid, but your other two examples raise grave doubts about this one.
The motion of the more massive pair will describe a smaller circle than the lighter one. The ratios of the two circles/motions allows you to calculate the unknown mass from the known.
Measuring the force of gravitation between two objects definitely doesn't measure the mass of those objects without resorting to weight; the weight is the quantity you're measuring. Similarly, the fact that the center of gravity for a two-objects-attached-by-a-string system will lie closer to the massier object relies on the massier object also being heavier. If the massier object weighs less, why do you believe the center of gravity would still be closer to it?
> I understand 'weight' as how heavy something is within particular gravity field (ie on a bathroom scale on earth) whereas mass is independent of local gravity. The schemes I suggest measure mass without resort to weight.
Yes, those are the definitions of weight and mass. We can measure weight directly, because it's a force and we have tools to measure those. All of our methods of determining the mass of something, as far as I know, rely on the assumption that if you know the gravitational field at a point, all objects with the same mass would, if located at that point, have the same weight. The most common method of determining an object's mass involves measuring the gravitational attraction between the object and the earth (colloquially known as the object's "weight"), and then imputing a mass to it based on that weight.
In the spinning example, I could say that two objects attached by a string and set spinning around each other will spin around a point that balances the torque from each object (this might not be, strictly speaking, correct, but it's close enough that I think it's suggestive). But torque is defined by force, not mass -- if one of the objects gets heavier without becoming massier, that should draw the center of rotation closer to that object, shouldn't it?
Or phrased yet another way: if one of the two attached objects is heavier than it "should be" according to its "true mass", then the two-objects-and-a-string system will have the center of mass and the center of gravity in different places. Those terms are currently synonymous, but if we had a novelty object such as undersuit described they would be distinct. Is there any reason to believe that the two-objects-and-a-string system would, if spinning, rotate around the center of mass rather than the center of gravity?
Tell someone to hold it. Turn it off. Watch them struggle with the sudden weight. Turn it back on.
Which would make space travel a lot easier - no more worrying about bone density loss!
This theoretical device could make things weight more than with just Earth's gravity... but it wouldn't help your spaceship. Your engine is still pushing out the same amount of matter, so thrust remains unchanged.
I, the spaceship, would like to accelerate through space. I take up some fuel and hurl it in the opposite direction, which requires me to apply force to the fuel I'm ejecting. It goes off into space at some rate determined by the impulse I applied and the mass of fuel I applied it to.
Newton's third law means that when I hurl the fuel, it applies a symmetrical impulse to me, accelerating me in the opposite direction.
In this model, the acceleration I get from the fuel doesn't depend in any way on the mass of the fuel I eject, only on the force I apply to it. What's wrong with the model?
Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is impossible with any physically reasonable detector. The reason is the extremely low cross section for the interaction of gravitons with matter. For example, a detector with the mass of Jupiter and 100% efficiency, placed in close orbit around a neutron star, would only be expected to observe one graviton every 10 years, even under the most favorable conditions. [...]
However, experiments to detect gravitational waves, which may be viewed as coherent states of many gravitons, are underway (such as LIGO and VIRGO). Although these experiments cannot detect individual gravitons, they might provide information about certain properties of the graviton. For example, if gravitational waves were observed to propagate slower than c (the speed of light in a vacuum), that would imply that the graviton has mass [...].
Fascinating! I take it that the question of whether the graviton could have mass is now considered to be well answered in the negative.
[0] https://en.wikipedia.org/wiki/Graviton