Starship Asterisk*

Chris Peterson wrote:

neufer wrote:

• Gravitons surely exist. The only reasonable question is whether gravitons are massless or not.

They certainly might exist. But all theory around them is speculative, poorly developed, and untested. So I find the best approach is simply to treat gravitational radiation as gravitational radiation, and not get too invested in any particular underlying mechanism.

neufer wrote:

• Gravitons surely exist. The only reasonable question is whether gravitons are massless or not.

RocketRon wrote:

~10⁷⁹ gravitons of average energy ~1 pico-electronvolt.
(~10²⁴ gravitons passed through every square centimeter of your body.)

And I didn't feel a thing....

https://en.wikipedia.org/wiki/Graviton wrote:
<<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. It would be impossible to discriminate these events from the background of neutrinos, since the dimensions of the required neutrino shield would ensure collapse into a black hole.>>

RocketRon wrote:
Gravity from the Sun, moon, other planets and more adjacent stars would be somewhat stronger, wethinks ?
Not to mention planet Earth.

RocketRon wrote:
Define too what a graviton is, precisely ?
And how we identify it when we 'see' one.

The Thing from Another World (1951) wrote:
Ned "Scotty" Scott: I bring you a warning: Tell the world, tell this to everybody wherever they are.

• Listen to the skies. Everywhere. Keep listening. Keep Listening to the skies.

RocketRon wrote:
And do gravitons meeting when travelling in opposite directions cancel each other out ??

• 1) travelling in opposite directions generate standing waves... while those
  2) travelling in the same direction but 180º out of phase cancel each other out.

neufer wrote:

Chris Peterson wrote:

50bmg wrote:
So, gravitons are carrying away the energy/mass?

I wouldn't say that, because gravitons are purely hypothetical particles. An elegant quantum treatment of gravity largely requires them, but we don't have such a treatment yet. So the safe answer is that gravitational radiation is the form the energy is in.

Gravitons surely exist. The only reasonable question is whether gravitons are massless or not

Chris Peterson wrote:

50bmg wrote:
Then, in the case of the merging black holes losing mass/energy -
Where did this mass/energy come from that was lost (3 solar masses in this case)? Are there now fewer particles (three solar masses worth of particles) in the converged black hole than there were in the two black holes?

The merged black hole has less mass than the sum of the progenitors. We don't know if black holes even have "particles" inside, so best not to go there. Somehow, mass escaped. Presumably that's something that happened right at the moment of merger, where the event horizon is very complex.

https://ned.ipac.caltech.edu/level5/March01/Carroll3/Carroll4.html wrote:
Lecture Notes on General Relativity
Sean M. Carroll, December 1997
Enrico Fermi Institute, University of Chicago

<<The nonlinearity of general relativity is worth remarking on. In Newtonian gravity the potential due to two point masses is simply the sum of the potentials for each mass, but clearly this does not carry over to general relativity (outside the weak-field limit). There is a physical reason for this, namely that in GR the gravitational field couples to itself. This can be thought of as a consequence of the equivalence principle - if gravitation did not couple to itself, a "gravitational atom" (two particles bound by their mutual gravitational attraction) would have a different inertial mass (due to the negative binding energy) than gravitational mass. From a particle physics point of view this can be expressed in terms of Feynman diagrams. The electromagnetic interaction between two electrons can be thought of as due to exchange of a virtual photon:

---

But there is no diagram in which two photons exchange another photon between themselves; electromagnetism is linear. The gravitational interaction, meanwhile, can be thought of as due to exchange of a virtual graviton (a quantized perturbation of the metric). The nonlinearity manifests itself as the fact that both electrons and gravitons (and anything else) can exchange virtual gravitons, and therefore exert a gravitational force:

---

There is nothing profound about this feature of gravity; it is shared by most gauge theories, such as quantum chromodynamics, the theory of the strong interactions. (Electromagnetism is actually the exception; the linearity can be traced to the fact that the relevant gauge group, U(1), is abelian.) But it does represent a departure from the Newtonian theory. (Of course this quantum mechanical language of Feynman diagrams is somewhat inappropriate for GR, which has not [yet] been successfully quantized, but the diagrams are just a convenient shorthand for remembering what interactions exist in the theory.)

The only reasonable question is whether gravitons are massless or not.

Chris Peterson wrote:

50bmg wrote:
So, gravitons are carrying away the energy/mass?

I wouldn't say that, because gravitons are purely hypothetical particles. An elegant quantum treatment of gravity largely requires them, but we don't have such a treatment yet. So the safe answer is that gravitational radiation is the form the energy is in.

• Gravitons surely exist. The only reasonable question is whether gravitons are massless or not.

https://en.wikipedia.org/wiki/Graviton wrote:
<<Gravitational waves may be viewed as the coherent states of many gravitons. If gravitational waves were observed to propagate slower than c, that would imply that the graviton has mass. Recent observations of gravitational waves have put an upper bound of 1.2 × 10^-22 eV/c² on the graviton's mass. 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 must couple to (interact with) the stress–energy tensor in the same way that the gravitational field does. If a massless spin-2 particle is discovered, it must be the graviton, so that the only experimental verification needed for the graviton may simply be the discovery of a massless spin-2 particle.

Click to play embedded YouTube video.

String theory predicts the existence of gravitons and their well-defined interactions. As closed strings without endpoints, they would not be bound to branes and could move freely between them. If we live on a brane 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.>>

50bmg wrote:So, gravitons are carrying away the energy/mass?

In a nuclear reaction where mass is lost in the form of radiated energy - are particles "turned into" photons as they radiate away, and in this way mass/energy is lost?

Then, in the case of the merging black holes losing mass/energy -
Where did this mass/energy come from that was lost (3 solar masses in this case)? Are there now fewer particles (three solar masses worth of particles) in the converged black hole than there were in the two black holes?

And, if so, did these particles "turn into" gravitons and radiate away mass/energy?

~1079 gravitons of average energy ~1 pico-electronvolt.
(~1024 gravitons passed through every square centimeter of your body.)

bmgriffi wrote:
Three solar masses were carried away when the two black holes converged. I know this has something to do with the mass-energy equivalence. In nuclear fusion, for example, the lost mass is carried away by photons, if I understand correctly. What is carrying away the lost mass in this case?

RocketRon wrote:T'wasn't me that wrote that.
Look back through this thread ...

I think you mean

I think you mean

RocketRon wrote:

A 10-19 "characteristic strain" for the 1km arm eLISA is a movement of 0.1 nanometers.

When the laser wavelength is 1064 nm

https://www.elisascience.org/articles/elisa-mission/sensitivity wrote:eLISA can achieve 10-21 strain resolution by measuring displacements of the order of fractions of a picometer. Its observations in the quiet environment of space will not be disturbed by seismic and gravity-gradient noise. Thus eLISA's unparalleled sensitivity will allow studying sources within the Galaxy and up to the edge of the visible Universe.

eLISA uses precision laser interferometry across 10⁶ km of space to compare separations between test masses that are protected by the spacecraft from non-gravitational disturbances. The distance measuring system is a continuous interferometric laser ranging scheme, similar to systems used for radar-tracking of spacecraft.

A 10-19 "characteristic strain" for the 1km arm eLISA is a movement of 0.1 nanometers.

"What we've measured in trying to record that signal is these two points in our interferometer, these two mirrors that are separated by four kilometres moved by an amount of an incredible 10-18 of a metre in a tenth of a second.
Even getting that concept of how small is 10-18 of a metre?
Well, it's 10,000 times smaller than a nucleus."

Ann wrote:
Thanks, Art. Would you care to comment on the figure? Is it easier or harder to detect supermassive merging black hole compared with stellar mass black holes? It should be easier, right?

Ann wrote:
And what is the "characteristic strain"?

Ann wrote:
The detected signal in this case came from two merging stellar-mass black holes. What if the black holes had been as massive as typical central supermassive black holes of galaxies? Imagine two central supermassive black holes merging, each containing as much mass as a million Suns.

What kind of gravitational wave signal would we see?

https://en.wikipedia.org/wiki/Evolved_Laser_Interferometer_Space_Antenna wrote:

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<<The Evolved Laser Interferometer Space Antenna (eLISA), previously called the Laser Interferometer Space Antenna (LISA), is a proposed European Space Agency mission designed to detect and accurately measure gravitational waves produced by compact binary systems and mergers of supermassive black holes. Each of the LISA spacecraft contains two telescopes, two lasers and two test masses, arranged in two optical assemblies pointed at the other two spacecraft. This forms Michelson-like interferometers, each centred on one of the spacecraft, with a the platinum-gold test masses defining the ends of the arms. The entire arrangement, which is ten times larger than the orbit of the Moon, will be placed in solar orbit at the same distance from the Sun as the Earth, but trailing the Earth by 20 degrees, and with the orbital planes of the three sciencecraft inclined relative to the ecliptic by about 0.33 degree, which results in the plane of the triangular sciencecraft formation being tilted 60 degrees from the plane of the ecliptic. The mean linear distance between the constellation and the Earth will be 50 million kilometers.

To eliminate non-gravitational forces such as light pressure and solar wind on the test masses, each spacecraft is constructed as a zero-drag satellite, and effectively floats around the masses, using capacitive sensing to determine their position relative to the spacecraft, and very precise thrusters to keep itself centered around them.>>

RocketRon wrote:

It is perfectly possible to observe the gravitational waves long before the actual collision,

Presumably this should have been expressed as

It is perfectly THEORETICALLY possible to observe the gravitational waves long before the actual collision,

since it hasn't been done yet, only modelled .... ?

It is perfectly possible to observe the gravitational waves long before the actual collision,

It is perfectly THEORETICALLY possible to observe the gravitational waves long before the actual collision,

daddyo wrote:

RocketRon wrote:How much advance notice are we likely to get of these events. ?
There is no indication that gravity waves preceded that brief flicker on the graph.
Its not like there is a continous stream of them, even at low intensity ??

The thought was observing the close orbits of two massive objects via gravity waves well ahead of the merger.