gravitons

Originally posted by @wolfgang59
I suppose you would have said that about atoms?
... and electrons (1897)
... the atomic nucleus (1911)
... protons (1920)
... neutrons (1932)
... neutrinos (1959)
... Higgs bosun (2012)

... but I admire the magnificence of your ignorance.

The ignorance is entirely on the side of science on this issue. We know what gravity does, but not what it is.

https://futurism.com/gravity-isnt-a-force-so-how-does-it-move-objects/

Gravity is a phenomenon of space-time. In order to quantize gravity (i.e., to know that some smallest unit or particle of gravity exists, call it a "graviton" if you wish), we would have to know that space too can be quantized (space-itons??). We do not know this either.

Some physicists are moving away from the terminology of calling gravity a "force", equivalent to electricity or light. We cannot measure attraction; what we can measure is some object accelerating towards some other object, but nothing in between "pulling" them. "Pulling" is not something we can measure; there's no there there.

When we detect gravitational waves, we are not measuring gravity per se; what we're measuring are discrepancies in light-beam-travel-times through a detector, discrepancies which, according to the presently accepted theories, are best explained as distortions in space-time.

https://www.space.com/31913-how-scientists-detected-gravitational-waves-ligo.html

A good metaphor for this is shaking a blanket: this sets up a standing wave on the blanket, but it would be a mistake to think that some particle of wool (if that is what the blanket is made of) is moving from one edge of the blanket to the other edge. This may be what gravity is like: i.e., waves in the 'fabric' of space-time, but without any particles (i.e., gravitons) moving from one place in the universe to another.

Originally posted by @lemon-lime
How can we rely on "the experts" when it's apparent even they can't agree on what causes gravity?

Nothing causes gravity. Nothing causes electricity either.

Originally posted by @moonbus
... Nothing causes electricity ...

what?
Friction can cause static electricity; dynamos turning can cause electricity in wires etc.

Originally posted by @humy
what?
Friction can cause static electricity; dynamos turning can cause electricity in wires etc.

Friction causes a charge to build up. Electricity and charge are not the same.

A turning dynamo does not cause electricity; it causes current. They are not the same.

If a magnet is moved through a coil of wire, current flows through the wire (that's what a dynamo does). Conversely, if a current is passed through a coil of wire and a magnet is within the coil, the magnet moves. But what is cause and what is effect here? That we do not observe. What we observe is that two phenomena are related, and we can express this relationship by exact mathematical formulas.

We can relate the amount of current in a coil to the speed and direction of motion of a magnet, and we can run it backwards and forwards (moving the magnet by hand to generate current, then releasing the magnet and applying current to the wire to move the magnet). However, there is no such thing as the strength of causality, or running causality backwards and forwards.

That is the sense in which nothing causes gravity. Gravity is an explanatory relationship between observable bodies which allows us to, for example, calculate the probable location and mass of an as-yet unknown planet when we observe perturbations in the orbits of known planets. Neither the known planet nor the presumed unknown one is causing gravity in this constellation.

Originally posted by @moonbus
Friction causes a charge to build up. Electricity and charge are not the same.

A turning dynamo does not cause electricity; it causes current. They are not the same.

If a magnet is moved through a coil of wire, current flows through the wire (that's what a dynamo does). Conversely, if a current is passed through a coil of wire and ...[text shortened]... r the known planet nor the presumed unknown one is causing gravity in this constellation.

Friction causes a charge to build up. Electricity and charge are not the same.

A charge build up then can cause current. Current and charge (as voltage) is electricity (more specifically, electric power).

A turning dynamo does not cause electricity; it causes current. They are not the same.

that current then goes on to cause an electric charge (voltage is difference in charge). Current and charge (as voltage) is electricity (more specifically, electric power).

If a magnet is moved through a coil of wire, current flows through the wire (that's what a dynamo does). ...But what is cause and what is effect here?

You already answered that;; "magnet is moved through a coil of wire" causes "current".
That current can then cause a difference in charge (somewhere) and current and difference in charge (voltage) combined is electricity (more specifically, electric power).

We know what causes electricity. We can define the physical laws for it. I think you may be confusing not knowing the 'cause' (if that makes sense here) of the physical laws with the physical laws leading to cause; the two aren't the same thing. The physical laws themselves may or may not be causeless (brute facts) but either way they define causations.
Somebody might know that the 'cause' of things falling is 'gravity' but not know the 'cause' (if any) of 'gravity' (as in the law of gravity); does that imply 'gravity doesn't 'cause' things to fall? I say not. Some X not having a 'cause' doesn't imply X cannot 'cause' Y (else you might get a nonsense infinite regress).

In the case of gravity, not sure if it even makes sense to speak of its 'cause'; if the bending of spacetime from the presence of mass IS 'gravity', does that mean you can say bending of spacetime from the presence of mass 'causes' gravity? -I think we could get into completely arbitrary and futile semantics and definitions here with a possible purely academic and pointless argument to rage over whether an "IS" semantically can sometimes equate with "cause"; it just depends on how you completely arbitrary define your terms and meanings.

"We know what causes electricity. We can define the physical laws for it."

Physical laws do not cause anything. They describe what happens; they do not make anything happen.

Originally posted by @moonbus
Friction causes a charge to build up. Electricity and charge are not the same.

A turning dynamo does not cause electricity; it causes current. They are not the same.

If a magnet is moved through a coil of wire, current flows through the wire (that's what a dynamo does). Conversely, if a current is passed through a coil of wire and ...[text shortened]... r the known planet nor the presumed unknown one is causing gravity in this constellation.

Maybe 'cause' isn't the right word to use for describing the relationship between mass and gravity. It does seem better to simply say that gravity is always found in the presence of mass, and mass is always found in the presence of gravity. However...
Imagine a universe devoid of time (you have space, but no spacetime). Mass could still exist, but not gravity. The existence of gravity is dependent upon mass in spacetime, but mass is not dependent on gravity for it to exist (at least theoretically). For this reason I think the idea of cause and effect does apply, but as more of a passive (rather than direct and active) form of causality.

Gravity is obviously indispensable for causing mass to clump together to form stars and planets and astroids and interstellar shopping malls, and what have you... my point is you can't have one (gravity) without the other (mass).


edit: I'm not entirely comfortable with a thought experiment that takes our universe and removes the element of time. Because then you have what appears to be a 3D still shot photo begging the question... is nothing moving (time) because there is no gravity, or is there no gravity because nothing is moving?

Originally posted by @lemon-lime
Maybe 'cause' isn't the right word to use for describing the relationship between mass and gravity. It does seem better to simply say that gravity is always found in the presence of mass, and mass is always found in the presence of gravity.


Gravity is obviously indispensable for causing mass to clump together to form stars and planets and astroids a ...[text shortened]... ing moving (time) because there is no gravity, or is there no gravity because nothing is moving?

"Gravity is obviously indispensable for causing mass to clump together to form stars and planets and astroids and interstellar shopping malls, and what have you... my point is you can't have one (gravity) without the other (mass)."

For a long time, physicists assumed that gravity must be a force, analogous to the strong and week atomic forces which hold atoms together; that is, people thought there must be something pulling masses together, the way one feels a magnet pulling iron towards it. This pullling is supposed to fill in a gap in our understanding of causality. Physicists are moving away from this thought-model. Physicists are coming round to the idea that there is no separate pulling going on between masses, it's not a third thing in addition to two masses which causes them to move towards each other.

Think of the surface of a blanket. Now put a ball on the blanket. It makes a dent in the surface; but this 'making a dent' is not something other than the ball on the blanket. Dents and ripples on the surface of the blanket are gravity. It's nothing in addition to the blanket or the ball. And no particle of the blanket is moving from one place to another. Now put another ball or other movable object on the blanket; the second ball changes the shape of the blanket locally, and therefore also has an 'effect' on other balls nearby on the blanket. That's the current model of gravity. But don't think that this 'effect' is something other than the ball on the blanket which makes a dent in the blanket.

If two big balls collide, it 'causes' ripples across the blanket. But don't think this 'cause' of the rippling is something separate to the blanket and the objects involved; it's a property of objects on the blanket. That is the current model of gravity.

"You can't have the one without the other." Well, that's like saying you can't have water without wet. They aren't two things (e.g., a man and his dog, and now one wants to know where is the leash which holds them together); there is a property of one thing. They are distinguishable (conceptually) but not separable (physically).

Now, the whole idea of gravitons is based on an analogy with electrons and photons, forms of energy which are packetized (which is to say, they come in discrete units). So it makes sense to ask, "Is there a smallest unit?" If it makes any sense to ask, "Is there a smallest dent in the fabric of space-time?" then there is case to be made for a smallest unit of gravity. Call it a "graviton" if you wish. But don't expect it to be something other than the smallest unit of mass (the smallest ball on the blanket).

A universe without time is a universe without change, a universe in which nothing happens.

There is no such thing as passive or active causality. Causality is not a force which makes things happen. Causality cannot be stronger or weaker. It's a conceptual relationship between phenomena.

Originally posted by @moonbus
"We know what causes electricity. We can define the physical laws for it."

Physical laws do not cause anything. They describe what happens; they do not make anything happen.

they describe what happens; and imply X causes Y.
As to "they do not make anything happen"; I could ague that is incorrect BUT now we are getting into the useless arbitrary semantics here I was speaking of earlier (how should you DEFINE "make anything happen"??); see last paragraph of my last post.

Presumably not everything has a 'cause'. If there is a 'cause' for a law A, what it the 'cause' of that 'cause' for law A? -now we will get into an infinite regress. Why cannot 'nothing causes' gravity?

Originally posted by @humy
they describe what happens; and imply X causes Y.
As to "they do not make anything happen"; I could ague that is incorrect BUT now we are getting into the useless arbitrary semantics here I was speaking of earlier; see last paragraph of my last post.

Presumably not everything has a 'cause'. If there is a 'cause' for a law A, what it the 'cause' of that 'cause' for law A? -now we will get into a infinite regress.

@humy: "Current and charge (as voltage) is [sic] electricity (more specifically, electric power)."

You're making a category mistake by putting voltage and current (for which there are indeed causes) on a level with electricity, analogous to putting orange and lemon on a level with fruit. One seed grows into a lemon tree, another seed grows into an orange tree; no seed grows into fruit, because fruit is not a thing, it's a category.

And now you're confusing (logical) implication with causality ("...imply X causes Y" ).

This is not mere semantics. It's about making sense.

Just drop it.

Originally posted by @moonbus
@humy: "Current and charge (as voltage) is [sic] electricity (more specifically, electric power)."

You're making a category mistake by putting voltage and current (for which there are indeed causes) on a level with electricity, analogous to putting orange and lemon on a level with fruit. One seed grows into a lemon tree, another seed grows into an orange ...[text shortened]... ...imply X causes Y" ).

This is not mere semantics. It's about making sense.

Just drop it.

You're making a category mistake by putting voltage and current (for which there are indeed causes) on a level with electricity,

No, I do not.
That is why I used the word "and" as in implying them being together as part of the same thing. Reminder; "...Current AND charge (as voltage)..". I know what electricity is.

And now you're confusing (logical) implication with causality ("...imply X causes Y" ).

No, I do not.
Under certain contexts that is exactly what some people but not all people sometimes mean by 'cause'; but now we are getting into pointless semantics.

This is not mere semantics.

Actually, it is

It's about making sense.

No, people can disagree about a definition but each still have a definition that "makes sense".

How do you define 'cause'?
If I give a different self-consistent definition of 'cause' that at least some people would agree with but is at odds with yours, why would your definition be right and mine wrong?

Originally posted by @metal-brain
If gravitons exist wouldn't that mean spacetime is discrete instead of continuous? Please explain.

The best way I can put this is to draw an analogy with ripples on the surface of a pond. The presence of the ripples certainly doesn't imply a discontinuous surface. A quantised wave is just one with a fixed amplitude - so I don't think that discontinuity is automatically implied by quantisation. Due to technicalities to do with the quantisation procedure I can't categorically rule it out either.

Originally posted by @moonbus
"Gravity is obviously indispensable for causing mass to clump together to form stars and planets and astroids and interstellar shopping malls, and what have you... my point is you can't have one (gravity) without the other (mass)."

For a long time, physicists assumed that gravity must be a force, analogous to the strong and week atomic forces which hold ...[text shortened]... appen. Causality cannot be stronger or weaker. It's a conceptual relationship between phenomena.

The catch is that what you are saying about gravity is in fact true of the other fields. The electromagnetic, strong and weak forces are gauge theories which are described in terms of structures known as principal bundles. Briefly, a principal bundle is a geometrical structure consisting of a base manifold, four dimensional space-time in this case, with a space identical to the symmetry group the corresponding force obeys connected at each point of the base space. In the simplest case, electromagnetism, the group is the circle group and so each point in space time has a circle associated with it. Electromagnetism is a consequence (within the theory) of vectors in the base space being components of vectors in the principal bundle.

The main difference between gravity and unquantised gauge theories is that the symmetry group SO(3,1) is open (the other forces' symmetry groups correspond to higher dimensional spheres or non-trivial products of higher dimensional spheres) this makes the theory non-unitary which causes all sorts of problems for the quantised theory - wavefunction aren't normalised which in most interpretations of quantum mechanics corresponds to the probability of finding a particle prepared in some initial state somewhere in the universe is different from one.

What the above means is that a description of gravity as an exchange force isn't invalidated because the particles being exchanged are quantised ripples in space-time.

Originally posted by @moonbus
"Gravity is obviously indispensable for causing mass to clump together to form stars and planets and astroids and interstellar shopping malls, and what have you... my point is you can't have one (gravity) without the other (mass)."

For a long time, physicists assumed that gravity must be a force, analogous to the strong and week atomic forces which hold ...[text shortened]... appen. Causality cannot be stronger or weaker. It's a conceptual relationship between phenomena.

There is no such thing as passive or active causality. Causality is not a force which makes things happen.

My bad, I wanted to make a distinction between cause and effect (A causes B, B causes C, etc) and how time coupled with space (spacetime) enables the existence of gravity. I'm calling this a passive relationship because (so far as I know) both time and space are massless... which means the fabric of spacetime is also massless.
( zero mass + zero mass = zero mass )

And if gravity is a property of spacetime then I'm assuming it too is massless, in spite of the fact it is able to influence the motion of objects that do have mass (physically exist).