What If Einstein Overlooked Something?

Discussions ranging from space technology, near-earth and solar system missions, to efforts to understand the large-scale structure of the cosmos.

What If Einstein Overlooked Something?

Postby socrat44 on October 18th, 2019, 9:24 pm 

Oct 17, 2019, 03:53pm
What If Einstein Overlooked Something?
/ Don Lincoln , Contributor /
---
'' . . . in order for gravity to act in the way in which it is observed,
which is to weaken between two objects as one over the square
of the distance separating them, the graviton has to have a handful
of properties. It must be massless, and it must travel at the speed of light. ''

https://www.forbes.com/sites/drdonlinco ... b929de4273

Gravity law: 1/r^2 = M/r^2
=====
Attachments
0.jpg
socrat44
Member
 
Posts: 398
Joined: 12 Dec 2015


Re: What If Einstein Overlooked Something?

Postby BurtJordaan on October 19th, 2019, 3:40 am 

Excellent non-technical article by Don.
Interesting the wordplay between the title and a later sentence:
Don wrote:But both measurements confirm that gravitons, if they exist, must be nearly massless or, quite possibly, exactly massless. This is what Einstein would have predicted.

I take it that Don meant that Einstein did predict gravitational waves that propagate at the speed of light, carrying energy, but that he did not make the connection to a massless particle carrying that energy, which is forced to propagate at the speed of light.

Don may correct me, but I have the impression that Einstein thought about quanta of gravitational energy, not about particles...?
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2713
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: What If Einstein Overlooked Something?

Postby socrat44 on October 19th, 2019, 6:30 am 

BurtJordaan » October 19th, 2019, 3:40 am wrote:Excellent non-technical article by Don.
Interesting the wordplay between the title and a later sentence:
Don wrote:But both measurements confirm that gravitons, if they exist, must be nearly massless or, quite possibly, exactly massless. This is what Einstein would have predicted.

. . . I have the impression that Einstein thought about quanta of gravitational energy,
not about particles...?

Newton's gravity ( inverse square law): 1/r^2 , M/r^2, Mass-zero: r=0, F=0
Can massless-graviton have energy ?
socrat44
Member
 
Posts: 398
Joined: 12 Dec 2015


Re: What If Einstein Overlooked Something?

Postby BurtJordaan on October 19th, 2019, 7:18 am 

socrat44 » 19 Oct 2019, 12:30 wrote: Newton's gravity ( inverse square law): 1/r^2 , M/r^2, Mass-zero: r=0, F=0
Can massless-graviton have energy ?


Yes, just like a massless photon carries energy, E=hf, the Planck-Einstein relation.
But:
https://en.wikipedia.org/wiki/Graviton wrote:While gravitons are presumed to be massless, they would still carry energy, as does any other quantum particle. Photon energy and gluon energy are also carried by massless particles. It is unclear which variables might determine graviton energy, the amount of energy carried by a single graviton.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2713
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)


Re: What If Einstein Overlooked Something?

Postby socrat44 on October 19th, 2019, 10:01 pm 

BurtJordaan » October 19th, 2019, 7:18 am wrote:
socrat44 » 19 Oct 2019, 12:30 wrote: Newton's gravity ( inverse square law): 1/r^2 , M/r^2, Mass-zero: r=0, F=0
Can massless-graviton have energy ?


Yes, just like a massless photon carries energy, E=hf, the Planck-Einstein relation.
But:
https://en.wikipedia.org/wiki/Graviton wrote:While gravitons are presumed to be massless, they would still carry energy, as does any other quantum particle. Photon energy and gluon energy are also carried by massless particles. It is unclear which variables might determine graviton energy, the amount of energy carried by a single graviton.

Graviton
There is no complete quantum field theory of gravitons . . .
the graviton is a massless state of a fundamental string. . . .
If it exists, the graviton is expected to be massless because
the gravitational force is very long range and appears to propagate
at the speed of light.
Additionally, it can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field would couple to the stress–energy tensor in the same way that gravitational interactions do. This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.
Theory
In the classical limit, a successful theory of gravitons would reduce to general relativity, which itself reduces to Newton's law of gravitation in the weak-field limit.
Gravitons in speculative theories
String theory predicts the existence of gravitons and their well-defined interactions. A graviton in perturbative string theory is a closed string in a very particular low-energy vibrational state. The scattering of gravitons in string theory can also be computed from the correlation functions in conformal field theory, as dictated by the AdS/CFT correspondence, or from matrix theory.[citation needed]
A feature of gravitons in string theory is that, as closed strings without endpoints, they would not be bound to branes and could move freely between them. If we live on a brane (as hypothesized by brane theories), this "leakage" of gravitons from the brane into higher-dimensional space could explain why gravitation is such a weak force, and gravitons from other branes adjacent to our own could provide a potential explanation for dark matter. However, if gravitons were to move completely freely between branes, this would dilute gravity too much, causing a violation of Newton's inverse-square law. To combat this, Lisa Randall found that a three-brane (such as ours) would have a gravitational pull of its own, preventing gravitons from drifting freely, possibly resulting in the diluted gravity we observe, while roughly maintaining Newton's inverse square law.[12] See brane cosmology.
A theory by Ahmed Farag Ali and Saurya Das adds quantum mechanical corrections (using Bohm trajectories) to general relativistic geodesics. If gravitons are given a small but non-zero mass, it could explain the cosmological constant without need for dark energy and solve the smallness problem.[13] The theory received an Honorable Mention in the 2014 Essay Competition of the Gravity Research Foundation for explaining the smallness of cosmological constant.[14] Also the theory received an Honorable Mention in the 2015 Essay Competition of the Gravity Research Foundation for naturally explaining the observed large-scale homogeneity and isotropy of the universe due to the proposed quantum corrections.
Difficulties and outstanding issues
Most theories containing gravitons suffer from severe problems.
Attempts to extend the Standard Model or other quantum field theories
by adding gravitons run into serious theoretical difficulties at energies close to or above the Planck scale.
This is because of infinities arising due to quantum effects; technically, gravitation is not renormalizable.
Since classical general relativity and quantum mechanics seem to be
incompatible at such energies, from a theoretical point of view,
this situation is not tenable.
One possible solution is to replace particles with strings.
String theories are quantum theories of gravity in the sense that they
reduce to classical general relativity plus field theory at low energies,
but are fully quantum mechanical, contain a graviton, and are thought
to be mathematically consistent.

https://en.wikipedia.org/wiki/Graviton
socrat44
Member
 
Posts: 398
Joined: 12 Dec 2015


Re: What If Einstein Overlooked Something?

Postby socrat44 on October 19th, 2019, 10:25 pm 

BurtJordaan » October 19th, 2019, 7:18 am wrote:
socrat44 » 19 Oct 2019, 12:30 wrote: Newton's gravity ( inverse square law): 1/r^2 , M/r^2, Mass-zero: r=0, F=0
Can massless-graviton have energy ?


Yes, just like a massless photon carries energy, E=hf, the Planck-Einstein relation.
But:

/ following the Planck-Einstein relation /
Planck–Einstein relation: E=h*w
The de Broglie's relation is also often encountered in vector form
p = ℏ*k ,
where p is the momentum vector, and k is the angular wave vector.
Bohr's frequency condition
is a direct consequence of the Planck–Einstein relation.
==============

@ BurtJordaan
Does graviton have these photon's characteristics?
socrat44
Member
 
Posts: 398
Joined: 12 Dec 2015


Re: What If Einstein Overlooked Something?

Postby BurtJordaan on October 20th, 2019, 2:48 am 

socrat44 » 20 Oct 2019, 04:25 wrote:@ BurtJordaan
Does graviton have these photon's characteristics?

No, AFAIK, photons and (hypothetical) gravitons are different in more than one aspect. For starters, photons are spin 1 and gravitons are spin 2 particles.

Further:

https://en.wikipedia.org/wiki/Graviton#Energy_and_wavelength wrote:...if gravitons are the quanta of gravitational waves, then the relation between wavelength and corresponding particle energy is fundamentally different for gravitons than for photons, since the Compton wavelength of the graviton is not equal to the gravitational-wave wavelength. Instead, the lower-bound graviton Compton wavelength is about 9×109 times greater than the gravitational wavelength for the GW170104 event, which was ~ 1,700 km. The report[16] did not elaborate on the source of this ratio. It is possible that gravitons are not the quanta of gravitational waves, or that the two phenomena are related in a different way.
User avatar
BurtJordaan
Forum Moderator
 
Posts: 2713
Joined: 17 Oct 2009
Location: South Africa
Blog: View Blog (9)
socrat44 liked this post



Return to Astronomy & Cosmology

Who is online

Users browsing this forum: No registered users and 6 guests