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It might be possible to detect gravitons after all

quantamagazine.org

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Re: It might be possible to detect gravitons after all

#141

Post by knodi123 »

revskill wrote: post #83

That means there's no Gravity before The BigBang, right ?

the big bang is a singularity; we can't ever experimentally learn anything about what came before it.

that doesn't mean there was no time before the big bang, or no gravity, or that there wasn't another universe just like ours. But due to the singularity, for the sake of convenience, we simply _say_ that those things came into existence at the big bang.

cite: https://www.hawking.org.uk/in-words/lectures/the-beginning-o... , search for "may as well"

Re: It might be possible to detect gravitons after all

#142

Post by jessriedel »

DebtDeflation wrote: post #65

The fact that QED and QCD are renormalizable while gravity is not is probably trying to tell us something deeper than we think. Relevant paper: https://arxiv.org/pdf/0709.3555 You can read the first two paragraphs of the Introduction and then skip to the last sentence of the Conclusion if you want to bypass all the math.

There are tons of effective QFTs that can be used very accurately to predict experiments below a certain (high) energy threshold, but which are not renormalizable. This is well understood. It means that the theory needs to be augmented to understand the higher energies, but does not at all mean the more fundamental (augmented) theory has to be radically different, such as classical. Everyone already agrees that the non-renormalizability of naive low-energy quantum gravity means something must be added.

Re: It might be possible to detect gravitons after all

#143

Post by DemocracyFTW2 »

tsimionescu wrote: post #61
DemocracyFTW2 wrote: post #58

Another goodie: > You need huge masses — think planets — to significantly warp space-time and generate obvious gravitational attraction. By way of comparison, a credit card-size magnet will stick to your fridge. By way of comparison, even an Olympic pool-size balloon of hot air will float.

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's worth of mass"?

BTW the comparison to the strong and weak nuclear forces is sort of strange too because not only do they only matter on nuclear scales, they also behave strangely not to an inverse-square law; Don Lincol of Fermilab explained that in a Feb 2024 video[1], from the description: "Popular science explanations [...] claim that some of the forces are stronger than others. What they don’t tell you is that all of those claims are only valid for distances comparable to the radius of a proton. For different size scales, the order of the strength of the forces can be wildly different."

Re: It might be possible to detect gravitons after all

#144

Post by DemocracyFTW2 »

criddell wrote: post #86
DemocracyFTW2 wrote: post #57

I choked on this part: > The discussion recalls a messy, largely forgotten episode from the dawn of the quantum era. In 1905, Einstein interpreted experimental data to mean that light is “quantized,” coming in discrete particles now called photons. Others, including Niels Bohr and Max Planck, thought that the classical, wave nature of light might still be saved. [...] Most physicists presume that everything in the wo…

> spare me that "war" simile It's not a simile, is it? They aren't saying it's like a war. My dictionary lists a bunch of definitions for war that fit this usage.

Yeah you're probably right, I'm not great on rhetoric vocab.

Re: It might be possible to detect gravitons after all

#145

Post by DemocracyFTW2 »

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

Yes, but. I have a 1920s edition of the Nibelungen Saga which uses an intentionally old-timey language; there I find "Wortstreit", obviously in contrast to a proper Streit which would have involved physic force and maybe weapons. But in modern German, as in English, to use "Streit" for an armed conflict or "war" for physicists discussing the nature of things is not appropriate except as a rhetoric measure (downplay or exaggerate). Words change.

Re: It might be possible to detect gravitons after all

#146

Post by DemocracyFTW2 »

evantbyrne wrote: post #88
DemocracyFTW2 wrote: post #57

I choked on this part: > The discussion recalls a messy, largely forgotten episode from the dawn of the quantum era. In 1905, Einstein interpreted experimental data to mean that light is “quantized,” coming in discrete particles now called photons. Others, including Niels Bohr and Max Planck, thought that the classical, wave nature of light might still be saved. [...] Most physicists presume that everything in the wo…

You seem to be frequently flame posting about America. Are you going to be okay?

I think I'm getting an anxiety disorder here seeing as close to 50% of Americans are seemingly OK with Trump, Vance and Elon becoming their new overlords. Seriously.

Re: It might be possible to detect gravitons after all

#147

Post by DemocracyFTW2 »

DemocracyFTW2 wrote: post #57

I choked on this part: > The discussion recalls a messy, largely forgotten episode from the dawn of the quantum era. In 1905, Einstein interpreted experimental data to mean that light is “quantized,” coming in discrete particles now called photons. Others, including Niels Bohr and Max Planck, thought that the classical, wave nature of light might still be saved. [...] Most physicists presume that everything in the wo…

Replying to myself as I can't edit my post now.

First things first, I didn't mean to stir up the discussion in this way. Also, I should have let go of the Caps Lock key. Also, I should've put all that stuff into a single comment or not write some of the things at all instead of creating multiple comments. Sorry.

As for the "inshallah", I probably used that word wrongly; I did not have any meaning of it in mind but used it—somewhat incomprehensibly so—as a moniker for "a standard to start any and all texts with", so "ceterum censeo Carthaginem esse delendam" if you will.

Re: It might be possible to detect gravitons after all

#148

Post by DemocracyFTW2 »

elashri wrote: post #112
DemocracyFTW2 wrote: post #57

I choked on this part: > The discussion recalls a messy, largely forgotten episode from the dawn of the quantum era. In 1905, Einstein interpreted experimental data to mean that light is “quantized,” coming in discrete particles now called photons. Others, including Niels Bohr and Max Planck, thought that the classical, wave nature of light might still be saved. [...] Most physicists presume that everything in the wo…

I will start by agreeing that usage of "war" seems weired. Although scientific drama in fundamental physics is not uncommon but a word like "debate" would be more appropriate. I don't like your usage of word "Inshallah" as a mock up of the idea that something will never happen. Because it is a complete opposite meaning of when you suppose to use it. It is usually overused by arab moms (I know that people tends to mea…

Please see my other comment; I used "inshallah" wrongly.

Re: It might be possible to detect gravitons after all

#149

Post by DemocracyFTW2 »

wasabi991011 wrote: post #121
DemocracyFTW2 wrote: post #57

I choked on this part: > The discussion recalls a messy, largely forgotten episode from the dawn of the quantum era. In 1905, Einstein interpreted experimental data to mean that light is “quantized,” coming in discrete particles now called photons. Others, including Niels Bohr and Max Planck, thought that the classical, wave nature of light might still be saved. [...] Most physicists presume that everything in the wo…

For 1): Yes, the photoelectric effect is frequently told. But that's not what the article is referring to here, it is foreshadowing its discussion on the semiclassical treatment of the photoelectric effect (by Lamb and Scully). This is the "messy, largely forgotten" part which is rarely discussed. I saw it in a graduate quantum optics course, but even at that level I'm not sure it's part of the standard curriculum.

OK that makes sense.

Re: It might be possible to detect gravitons after all

#150

Post by DemocracyFTW2 »

Sniffnoy wrote: post #139
DemocracyFTW2 wrote: post #57

I choked on this part: > The discussion recalls a messy, largely forgotten episode from the dawn of the quantum era. In 1905, Einstein interpreted experimental data to mean that light is “quantized,” coming in discrete particles now called photons. Others, including Niels Bohr and Max Planck, thought that the classical, wave nature of light might still be saved. [...] Most physicists presume that everything in the wo…

The "forgotten" part isn't Einstein's proposal, but the semiclassical suggestion of how to avoid it. Have you seen that part commonly retold? I haven't.

I agree, I misread that.
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