Timeline for If gravity is a pseudoforce in general relativity, then why is a graviton necessary?
Current License: CC BY-SA 4.0
23 events
| when toggle format | what | by | license | comment | |
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| Oct 10, 2020 at 1:56 | comment | added | Sagar Patil | I personally don't agree with the statement of the elephant. I thought the reason you feel a force from an elephant's foot is that you are just feeling the normal force applied onto the elephant by you? | |
| Jan 15, 2019 at 20:08 | comment | added | JPattarini | Forgive my basic question, but I don’t see the driver for quantization of the metric except in boundary cases - energy should be able to take on continuous values for any free particle, so why the need to quantize? | |
| Dec 27, 2018 at 5:44 | history | edited | John Rennie | CC BY-SA 4.0 |
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| Dec 27, 2018 at 4:52 | comment | added | Dawood ibn Kareem | I actually think that somebody who's been thrown off the back of a rapidly spinning elephant might attest that gravity is no more real than centrifugal force. | |
| Dec 26, 2018 at 10:21 | comment | added | John Rennie | @HopelessN00b I think you might be taking my attempt to introduce a little humour more seriously than it deserves :-) | |
| Dec 26, 2018 at 10:16 | comment | added | HopelessN00b | Having an elephant sit on you seems like one of those once-in-a-lifetime experiences... in the sense that it would be fatal. At the very least, I doubt anyone who’s had an elephant sit on them would be in state to attest about anything, what with the feeding tubes and mechanical lungs and medically induced coma and such. | |
| Dec 25, 2018 at 18:17 | comment | added | Peter Shor | This doesn't really answer the question. What you're saying that quantizing gravity isn't quantizing a force, but quantizing a metric. But I think the question the OP is interested in is: what goes wrong if you try to make a theory of physics where gravity isn't quantized? | |
| Dec 25, 2018 at 3:26 | comment | added | JBentley | I'm not convinced that anyone who has been sat on by an elephant can attest to anything. | |
| Dec 24, 2018 at 18:42 | history | edited | John Rennie | CC BY-SA 4.0 |
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| Dec 24, 2018 at 18:17 | history | edited | John Rennie | CC BY-SA 4.0 |
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| Dec 24, 2018 at 17:42 | comment | added | Acccumulation | "The force itself it most certainly not fictitious as anyone who has been sat on by an elephant can attest." An elephant in a centrifuge would produce a "centrifugal force", that doesn't mean centrifugal force isn't "fictitious". | |
| Dec 24, 2018 at 11:55 | comment | added | AncientSwordRage | I have never been sat on by an elephant, therefore I will still attest to gravity being fictitious. | |
| Dec 23, 2018 at 21:35 | comment | added | JiK | "The force itself it most certainly not fictitious as anyone who has been sat on by an elephant can attest." I bet Mr. Bond can attest that the centrifugal force is most certainly not fictitious, either. | |
| Dec 23, 2018 at 8:31 | comment | added | The_Sympathizer | And in order to make it happen that you can have an inertial force with the geometrical complexity of gravitation (i.e. the ability to pull harder or softer when near or far from many different planets or other objects scattered throughout space, to have inhomogeneities due to their varying density, etc.), you need to modify the geometry of spacetime. | |
| Dec 23, 2018 at 8:28 | comment | added | The_Sympathizer | And in gravitation, the inertial force appears when you consider an observer fixed to, say, the surface of a gravitating planet, who sees things falling as being "pulled" by a force. This is because the surface of a gravitating planet is not an inertial frame. | |
| Dec 23, 2018 at 8:26 | comment | added | The_Sympathizer | In particular, inertial forces treat all objects the same in that they accelerate them independently of the properties of those objects, and if they vary, they only do so by purely geometric properties. Electromagnetic forces don't do this. Two objects of different charges accelerate differently, and if you have differently-charged objects on hand you can locally determine if there is/isn't an electric field present, even if you are being pulled by it due to some charge on you. | |
| Dec 23, 2018 at 8:25 | comment | added | The_Sympathizer | The term "fictitious" force, I believe, here, is actually best understood as being not in the sense of "not real" but rather in the sense of "centrifugal force", and what it's saying is that gravity is exactly the same kind of "force" as centrifugal force. That is, it is something which may be better called an "inertial force", which arises from operating in a non-inertial reference frame. In particular, the key is that a free-fall frame is an inertial frame, in that you cannot do any experiments at least "locally" to tell that you are falling versus simply moving through empty space. | |
| Dec 23, 2018 at 7:58 | comment | added | InertialObserver | Why is that? Isn't $A^\mu(x)$ a function of space time? | |
| Dec 23, 2018 at 7:57 | comment | added | John Rennie | No I don't think quantising the metric is any more fundamental than quantising the electromagnetic potential fourvector. | |
| Dec 23, 2018 at 7:54 | comment | added | InertialObserver | But isn't OP asserting the possibility that gravity is different in this sense? That the description of spacetime is more fundamental than the Yang-Mills gauge theories that we define on that spacetime, and so perhaps shouldn't be subject to the same intuition that it should be "quantized"? | |
| Dec 23, 2018 at 7:44 | comment | added | John Rennie | @InertialObserver yes | |
| Dec 23, 2018 at 7:40 | comment | added | InertialObserver | I really like this answer, and the link is very good too. But when you say "There is a sense in which all forces are fictitious since they are all the emergent long range behaviour of quantum fields", are asserting that this is equivalent to your earlier statement that "the force is the result of an underlying property"? | |
| Dec 23, 2018 at 7:33 | history | answered | John Rennie | CC BY-SA 4.0 |