Quantized Gravity

[geordief]

Would  there be  any practical,verifiable consequences of gravity having a quantized nature?

 

Would it follow that  at finite distances  global expansion would take over and ,calving -iceberg-like it would be farewell to the  outer regions of the universe? (if gravity is the only force capable of causing global contraction at extreme distances)

 

ps wasn't  there some recent story about possibly testing this using entanglement?

 

Edited September 25, 2018 by geordief

[koti]

16 minutes ago, geordief said:

 

ps wasn't  there some recent story about possibly testing this using entanglement?

 

You might find this interesting:

https://www.quantamagazine.org/physicists-find-a-way-to-see-the-grin-of-quantum-gravity-20180306/

 

[Rajiv Naik]

gravitational waves means gravity quantaised.

[beecee]

24 minutes ago, Rajiv Naik said:

gravitational waves means gravity quantaised.

No it does not.

[Rajiv Naik]

why not ?

than what are gravitons ?

 

[Rajiv Naik]

since I have been told that I am putting my own ideas here, I would like to clarity that what I put here is usually derived from reliable sources - 

I am not a scientist, but try to read a lot from good science sources

for instanceone of latest article from scientific american I am quoting as it relates to the topic here .

I can give hundreds of oher references from top scientists in the world for my every comment on this forum

If I am permitted. 

scientific american article :

Quach, now at the University of Adelaide in Australia, suggested a way to detect gravitons by taking advantage of their quantum nature. Quantum mechanics suggests the universe is inherently fuzzy—for instance, one can never absolutely know a particle's position and momentum at the same time. One consequence of this uncertainty is that a vacuum is never completely empty, but instead buzzes with a “quantum foam” of so-called virtual particles that constantly pop in and out of existence. These ghostly entities may be any kind of quanta, including gravitons.

...

Although Norte’s microchip did not discover whether gravity is quantum, other scientists are pursuing a variety of approaches to find gravitational quantum effects. For example, in 2017 two independent studies suggested that if gravity is quantum it could generate a link known as “entanglement” between particles, so that one particle instantaneously influences another no matter where either is located in the cosmos. A tabletop experiment using laser beams and microscopic diamonds might help search for such gravity-based entanglement. The crystals would be kept in a vacuum to avoid collisions with atoms, so they would interact with one another through gravity alone. Scientists would let these diamonds fall at the same time, and if gravity is quantum the gravitational pull each crystal exerts on the other could entangle them together.

The researchers would seek out entanglement by shining lasers into each diamond’s heart after the drop. If particles in the crystals’ centers spin one way, they would fluoresce, but they would not if they spin the other way. If the spins in both crystals are in sync more often than chance would predict, this would suggest entanglement. “Experimentalists all over the world are curious to take the challenge up,” says quantum gravity researcher Anupam Mazumdar of the University of Groningen in the Netherlands, co-author of one of the entanglement studies.



Another strategy to find evidence for quantum gravity is to look at the cosmic microwave background radiation, the faint afterglow of the big bang, says cosmologist Alan Guth of M.I.T. 

One more way to find out whether gravity is quantum is to look directly for quantum fluctuations in gravitational waves, which are thought to be made up of gravitons that were generated shortly after the big bang. The Laser Interferometer Gravitational-Wave Observatory (LIGO) first detected gravitational waves in 2016, but it is not sensitive enough to detect the fluctuating gravitational waves in the early universe that inflation stretched to cosmic scales, Guth says. A gravitational-wave observatory in space, such as the Laser Interferometer Space Antenna (LISA), could potentially detect these waves, Wilczek adds.

In a paper recently accepted by the journal Classical and Quantum Gravity, however, astrophysicist Richard Lieu of the University of Alabama, Huntsville, argues that LIGO should already have detected gravitons if they carry as much energy as some current models of particle physics suggest. 


.
    Charles Q. Choi
Charles Q. Choi is a frequent contributor to Scientific American. His work has also appeared in The New York Times, Science, Nature, Wired, and LiveScience, among others. In his spare time, he has traveled to all seven continents.

 

as per new look at hysenbergs uncertainity position of particle cannot be determined because every time its new particle.

[beecee]

5 hours ago, Rajiv Naik said:

why not ?

than what are gravitons ?

 

Gravitons are a hypothetical concept, not yet validated.

https://en.wikipedia.org/wiki/Graviton

"In theories of quantum gravity, the graviton is the hypothetical elementary particle that mediates the force of gravity".

Simply put, as yet we do not have any validated QGT.

Edited November 22, 2018 by beecee

[Rajiv Naik]

there was gravitational wave last year detected by ligo. it was recorded at least at two places..

I presume there cannot be concept of wave without particles. ie gravitons

so  Why you say it was not detected - it is bound to be validated, isnt it ?  

 

[StringJunky]

38 minutes ago, Rajiv Naik said:

there was gravitational wave last year detected by ligo. it was recorded at least at two places..

I presume there cannot be concept of wave without particles. ie gravitons

so  Why you say it was not detected - it is bound to be validated, isnt it ?  

 

They haven't yet been able to work out how to quantify gravity into a discrete unit, like photons, which is necessary to define it as a particle.  That's why gravitons are still theoretical.

Edited November 22, 2018 by StringJunky

[Rajiv Naik]

but fact remains that there are gravitons - May be properties and nature is not known.

[beecee]

17 minutes ago, Rajiv Naik said:

but fact remains that there are gravitons - May be properties and nature is not known.

No, scientists remain unsure whether gravity can be quantised or not.

[Ghideon]

Thanks for the article*, I'll read it once I get some time.

57 minutes ago, Rajiv Naik said:

but fact remains that there are gravitons

Ok, but the article you quoted says it is unsure:

5 hours ago, Rajiv Naik said:

Lieu suggests it might also mean the graviton does not exist

 

>Off topic joke

5 hours ago, Rajiv Naik said:

as per new look at hysenbergs uncertainity position of particle cannot be determined

It would be easier if you added a link to the article, so I suppose the above should read: "as per new look at Heisenbergs uncertainty position of article cannot be determined"

<end of joke

 

*) I suppose it is this one: https://www.scientificamerican.com/article/is-gravity-quantum?

[beecee]

3 hours ago, Rajiv Naik said:

there was gravitational wave last year detected by ligo. it was recorded at least at two places..

I presume there cannot be concept of wave without particles. ie gravitons

so  Why you say it was not detected - it is bound to be validated, isnt it ?  

A gravitational wave is not a particle....Gravity/spacetime can be warped, curved, twisted and waved in the presence of mass. Gravity is spacetime. Gravity is geometry. 

[swansont]

5 hours ago, Rajiv Naik said:

If I am permitted. 

scientific american article :

 

 

!

Moderator Note

No, you are not. You can quote relevant sections but not the entire article. Your post has been edited.

Further, you should link to the article.

https://www.scientificamerican.com/article/is-gravity-quantum/

 

[Rajiv Naik]

16 hours ago, swansont said:

 

!

Moderator Note

No, you are not. You can quote relevant sections but not the entire article. Your post has been edited.

Further, you should link to the article.

https://www.scientificamerican.com/article/is-gravity-quantum/

 

 

ok , let me explain what I meant by gravitons.

as per my  understanding from what I have read: wave is a radiation with  Perticular energy (frequency) and hence perticular amplitude  affecting particles of the medium in which it propogates.

after receiving the energy from the wave the particle fluctuates or oscillates and transfer the energy it received to next particle, thereby helping wave to propagate to next particle placed at given amplitude.

therefore when we observe the wave at given pt. We see oscillating particle : not a moving particle. (hysenbergs principal ?)

therefore when there is gravitational wave travellig through spacetime fabric it has to have medium or particle propogating the waves.

its energy must also be quantised, or else it can not be a gravity wave.

In string theory it is proposed that strings are open in case of gravity and hence it can travel beyond our universe also .

there are more interestig Proposition by  topmost scientist in theorotical Physics today.

 

however, some people here are greater physicists. .. so  I would like to be enlightened Just kidding.

seriously. ...We are all curious people here , somebody can explain to me if I am wrong , so I can understand better - instead of -no its wrong- 

I think acting too orthodoxically  is antithesis of science.

 

[swansont]

42 minutes ago, Rajiv Naik said:

 its energy must also be quantised, or else it can not be a gravity wave.

!

Moderator Note

You need to explain your reasoning here. This was pointed out before. Why must it be quantized?

 

 

[Rajiv Naik]

according to my understanding-

for other elementary particles in standard model. Term quantised has no fixed parameters. 

its complicated process to quantise  energy (including mass) for other fundamental particles which too are radiation waves. its dynamic process. 

but spectrum defines them to quite an extent.

I thinkrest mass can not be quantised as its really a form of potential energy - due   to dynamicsof radiation -

thus broadly speaking when wave is identified it should be quantised at least for some of the parameters is a rational conclusion one can draw..

[beecee]

7 hours ago, Rajiv Naik said:

 

ok , let me explain what I meant by gravitons.

 

therefore when there is gravitational wave travellig through spacetime fabric it has to have medium or particle propogating the waves.

its energy must also be quantised, or else it can not be a gravity wave.

As I mentioned before, gravity is simply geometry or warped, twisted, undulating spacetime. Gravitational waves are undulations of this same spacetime. Again, as yet we have no verifiable theory of  quantized gravity/spacetime.

Quote

I think acting too orthodoxically  is antithesis of science.

All science and scientific theories begin as speculation. Speculative science has to be defined separately from evidence based scientific theories.

Quote

according to my understanding-

You seem to have a great interest in science, particularly cosmology. That's admirable. But a tip from myself, who also like you has a great interest in cosmology, but with no real formal education in that discipline, is that as an amateur, you must be aware that most of our science presenters  on TV etc, are giving simplified versions of certain aspects of science. Pop science mags and presentations have there place, but again, need to be accepted with that proviso that it is by necessity simplified.

If you read something, or hear something interesting, get it verified on forums such as this by those educated in that discipline...again, I'm not one of them, but I have tempered my enthusiasm and first impressions by more advanced readings such as Kip Thorne's Black Holes and Time Warps, and separating speculation from scientific theory.

Edited November 23, 2018 by beecee

[studiot]

14 minutes ago, beecee said:

As I mentioned before, gravity is simply geometry or warped, twisted, undulating spacetime. Gravitational waves are undulations of this same spacetime. Again, as yet we have no verifiable theory of  quantized gravity/spacetime.

That is one view.

A different one is that gravity breaks one of the symmetries of isotropic space, in that it introduces a preferred direction.

[MigL]

The graviton is a 'consequence' of the quantization of the gravitational field, as quantum field theory has, by necessity, a 'carrier' particle ( quantum ).

Gravitational waves, on the other hand, are a consequence of GR; a strictly classical theory, involving no quantization, and no gravitons.

IE, without a quantum field theory of gravity, there is no graviton.
( but since QG is postulated,  the graviton is also postulated )

[Rajiv Naik]

2 hours ago, MigL said:

The graviton is a 'consequence' of the quantization of the gravitational field, as quantum field theory has, by necessity, a 'carrier' particle ( quantum ).

Gravitational waves, on the other hand, are a consequence of GR; a strictly classical theory, involving no quantization, and no gravitons.

IE, without a quantum field theory of gravity, there is no graviton.
( but since QG is postulated,  the graviton is also postulated )

how existance or nonexistance of gravity depends on theories which postulates it.

there are many theories - not only general relativity or quantum field  theory.

there is explainnation in string theory and superstring theory also - which postulates gravity as open and free string which can travel between universes also- a only link we may have to other universes.

[studiot]

2 hours ago, Rajiv Naik said:

how existance or nonexistance of gravity depends on theories which postulates it.

Trying to find out is good +1

MigL has given you some very important information, though very compact and condensed.

In order to unravel and expand this, please answer the following question.

 

Do you know what a periodic function is? For example a sine function.

I assume you know what a function is in broad terms.

[Rajiv Naik]

What I know is:

sine functions is not only a mathematical trignometric angular function - it has  much more meaning than measuring properties of waves like frequency and amplitude .

unit angular vector also has more meaning to it- but it would be very long explaination.a cosmological constant could be one day explained  by it. GR is uncertain about it.

Sinwave function represents  fundamental property governing  the manner in which information wave in our spacetime is allowed to propogate.

however I think it is assumed here that gravitons and gravitational wave are two different phenomenons?

as per my knowledge gravitons are fluctuations caused in spacetime  by gravitational wave - it affects spacetime fabric- and hence the time, as it affects the photons Waves  (light)travellig  in spacetime fabric.

I feel what I am saying here is not old mainstream physics tought in colleges, and hence I dont know where your pt. is headig to,

if debated further  I can explain. - but I need to know whats your view about sine wave  - 

 

 

 

 

[studiot]

15 minutes ago, Rajiv Naik said:

What I know is:

sine functions is not only a mathematical trignometric angular function - it has  much more meaning than measuring properties of waves like frequency and amplitude .

unit angular vector also has more meaning to it- but it would be very long explaination.a cosmological constant could be one day explained  by it. GR is uncertain about it.

Sinwave function represents  fundamental property governing  the manner in which information wave in our spacetime is allowed to propogate.

however I think it is assumed here that gravitons and gravitational wave are two different phenomenons?

as per my knowledge gravitons are fluctuations caused in spacetime  by gravitational wave - it affects spacetime fabric- and hence the time, as it affects the photons Waves  (light)travellig  in spacetime fabric.

I feel what I am saying here is not old mainstream physics tought in colleges, and hence I dont know where your pt. is headig to,

if debated further  I can explain. - but I need to know whats your view about sine wave  - 

 

 

 

 

OK, thank you for what you have told me.

But you did not answer my question.

I asked

3 hours ago, studiot said:

Do you know what a periodic function is? For example a sine function.

Look carefully at where the question mark is.

I did not ask if you know what a sine function is, I gave it as an example.

All too often students do exactly this in exams and answer the wrong question (which was not asked).

 

The whole point of periodic functions is they they lead back to or feed into MigL's short post about Quantum Theory in general.

Since you have answered sensibly I am going to have a quick punt here to push the discussion on.

A periodic function has y = f(x) has the same value y for (indefinitely) many values of x.
So the graph or plot of the function repeats itself periodically or at regular intervals of x.

As a result, if we know one solution at one value of x, say y₁ =  f(x₁),

we can write a solution in terms of n times x₁ where n is an auxiliary counting variable

so y_n = nf(x_n)

Hopefully you can see how this is true for the sine function y = sin(x).

 

So what does this have to do with Quantum Mechanics and Gravity? - The subject of this thread

 

Well if you have a solution to an equation for some property of a system which is a periodic function then it can be written in the form just shown.

Generally in QM this property refers to energy (though it may be more complicated) and the solutions are periodic (though more complicated than sine functions).

In turn this leads to quantum levels of energy and the resultant transitions between them having distinct values being the difference between them.

It is an axiom or proposition of Quantum Theory that the values of x and y between these values are 'forbidden' to the system.

There may also be other, non periodic, solutions with no forbidden values over a certain range.
These are often called the continuum solutions that occur once a certain energy threshold has been exceeded. For example when an electron has sufficient energy to leave an atom.

 

In Wave theory the properties involved are somewhat different and there are no forbidden values of x and y.
It is also axiomatic that there are no other solutions to the equations.

 

I think that is enough for now, but there is a lot of water to pass under the bridge yet.