Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

It might be possible to detect gravitons after all

quantamagazine.org

Post reply on HN
Print view View original

161–167 of 167 posts

Re: It might be possible to detect gravitons after all

#161

Post by cryptonector »

Wololooo wrote: post #45
NitpickLawyer wrote: post #39

Earlier quoted context omitted.

I last took a physics course when Pluto was a planet, so excuse my possibly outdated question, but isn't the detection of gravitational waves proof of gravity being a force? I follow a few educators/communicators in this field and I have a feeling they're using this "gravity isn't really a force" to bridge the gap between their deep understanding and us mortals that don't poses the language / understanding to get the…

So the main issue here is how people were presenting it, in Quantum field theory, as stated by other people, each force is associated with a field and has at least one force carrier, the exact number is linked to the specifics of the mathematical framework underlying it To that extent you can build 3 fundamental forces, electro magnetic, weak (that are called together electroweak) and the strong force. You have an ex…

> The main issue with gravity is that it is interpreted so far as a curvature of space time,

Yes, that is the main issue. It doesn't have to be that way though. If you look at the Einstein field equations, and solutions like the Schwarzschild and Kerr metrics, the key component is a metric tensor that is nothing more than a mapping from flat spacetime to curved spacetime. We have the ability to choose which interpretation to use. The metrics are nothing more than Mercator-like projections.

If you take the curved spacetime view then you get distortions of spacetime. If you take the flat spacetime view then you get other distortions like that the speed of light -though always seen as the same locally- varies according to the gravitational potential (there are other distortions as well).

We seem to have a bit of a fetish for the curved spacetime view. But oddly when you look for animations depicting interactions with black holes and photons or particles / small bodies what you almost invariably find are of two types: a) flat spacetime representations, or b) the funnel representation, and (b) often comes with a flat spacetime representation above the funnel. How do you think the authors produce the flat spacetime representations? A: By applying the metrics to go from curved spacetime to flat! And why do they use flat spacetime for their animations? A: Because it's easier for humans to understand!

The reality is that flat and curved spacetime are two sides of the same coin. If curved spacetime is the sticking point for quantizing gravity, then switch to flat spacetime.

Re: It might be possible to detect gravitons after all

#163

Post by KolenCh »

Aardwolf wrote: post #111
FeepingCreature wrote: post #47

Earlier quoted context omitted.

> Can you please elaborate, the first part of the sentence says graviton is for non-self-interacting gravity, the second part of the sentence says graviton is for self-interacting (if 'its' in 'its self-interaction' refers to the graviton). The point is, we know gravitation does self-interact. But our best model, the graviton, doesn't model self-interaction. So the model is probably accurate in regimes where you'd ex…

Would self-interaction mean something like: just like the massless photon, the massless graviton would be bent by the gravity of black holes... hence self interaction?

Photon-photon interaction is photon self interaction. Gravity/graviton self interaction then means graviton-graviton interaction. In general relativity, all form of energy would have an effect of gravity, and also react to gravity. Since all matter, including photon and graviton, has energy, then they should self interact.

In QED, photon and photon do interacts too and you can calculate its effect to be small. In GR, you can expect self interaction is small if the space time curvature is small.

(Photon is the particle that mediates QED, and graviton is the hypothetical particle that mediates gravity.)

Re: It might be possible to detect gravitons after all

#164

Post by goodpoint »

seanhunter wrote: post #138
goodpoint wrote: post #87

Earlier quoted context omitted.

> Please spare me that "war" simile +1, normalizing "war" as a synonym of effort is pretty much orwellian.

That is part of the original etymology of the word. [1] > late Old English wyrre, werre "large-scale military conflict," from Old North French werre "war" (Old French guerre "difficulty, dispute; hostility; fight, combat, war;" Modern French guerre), Note the old French part including difficulty dispute, hostility and fight. [1] https://www.etymonline.com/word/war

What you described is not a synonym of "effort".

Plus, in terms of number of civilian casualties modern wars make ancient wars look like skirmishes. Another reason not to dilute the word "war".

Re: It might be possible to detect gravitons after all

#165

Post by goodpoint »

seanhunter wrote: post #152
zeroonetwothree wrote: post #140

Earlier quoted context omitted.

Wow, words changing meaning over time. Imagine that. The internet would lead me to believe that’s something horrific that must not be allowed.

The OP doesn't like the meaning of the word "war" changing from a definition they believe to be correct. My example shows that the meaning of words is defined by usage and that usage changes over time. This is especially ironic in this particular case because the meaning that the OP didn't like is one which was actually part of the original etymology of the word.

> This is especially ironic in this particular case because the meaning that the OP didn't like is one which was actually part of the original etymology of the word.

No, it wasn't. Plus I never said that the meaning of a word is written in stone and cannot change "just because".

Re: It might be possible to detect gravitons after all

#166

Post by gradschoolfail »

gus_massa wrote: post #75
lazide wrote: post #62

Earlier quoted context omitted.

Because they don’t want to run the risk of being wrong, eh?

Probably because the number of detection will be too few to test old theories or make new theories with the experimental results. Physicists love to be wrong! If there is an experiment that disagree with the current theory, then is like the will west and everyone can publish their own pet theory that "fix" it. It's like raining free paper for them, their graduate students and everyone. Also, it's fun! When experiment…

Haha i remember! friends got caught up in that! (Wasnt it 3-sigma tho?)

Theorists would also love for experimentalists to be wrong, but the most efficient way to do it would be by inventing new maths… [sad but still fun]

Re: It might be possible to detect gravitons after all

#167

Post by tsimionescu »

DemocracyFTW2 wrote: post #143
tsimionescu wrote: post #61

Earlier quoted context omitted.

It's not clear what problem you have with that comparison. It's a classical example of just how weak gravity is compared to the electromagnetic interaction. A whole planet's worth of mass is weaker than the EM field generated by a tiny magnet. And the strong and weak nuclear interactions are even stronger still.

I just found it funny that the author uses such a specific measure for an object that typically looks nothing like a credit card. I think the only credit-card sized magnet I've ever seen might have been an elastic magnetized floppy piece of plastic that was rather weak (I think it was used to fix paper on sheet metal). How about "even a small magnet can pull up things and overcome the gravity caused by a whole planet…

Credit-card shaped and sized magnets are actually pretty popular as tourist mementos. It's true that they are typically slightly smaller than a credit card, but they're a common occurrence.

And while it's true that the strong force has very complex interactions which make it both stronger and weaker than EM in certain situations, I don't think there is any situation in which EM is weaker than gravity. Of course, the comparison is ultimately apples-to-oranges, as it basically amounts to comparing the amount of electrical charge to the amount of "mass charge". Still, if we compare by, say, the total number of particles with mass/charge respectively of any kind you need two bodies to have to have an equivalent effect on motion through gravitational VS EM interactions, in every situation that we know how to model, you would end with the same conclusion.

Post reply on HN