The Dark Energy of a Theoretical Physicist | Hacker News Reader

The Dark Energy of a Theoretical Physicist

newyorker.com

37 pointsmathgenius21 comments

There's a tendency in the popular science world and the physics world to glorify high energy physics, and string theory and all that goes along with it.

It's definitely useful - After reading one of those books I was pretty convinced I wanted to do a PhD in Physics. I'm currently four years into a PhD in physics, except in something completely removed from what she works on.

There is also a tendency to elevate theorists and denigrate experimentalists. The experimentalists work is often portrayed as 'dull and technical' and they only worry about the details, whereas the theorist dreams up these wild theories in flights of genius. I can't speak for anyone else, but this was true of school where I was from.

I'm just a little tired of this fairly one dimensional portrayal of physicists (theoretical or otherwise). There's plenty of interesting stuff out there that doesn't involve dark matter or strings (or quantum field theory!). Fluid dynamics is endlessly fascinating to me, or non linear systems ("chaos theory").

Lisa Randall is a phenomenal physicist and I don't begrudge the author her admiration - There just need to be more pieces like this about other facets of the sciences.

"The experimentalists work is often portrayed as 'dull and technical' and they only worry about the details, whereas the theorist dreams up these wild theories in flights of genius. I can't speak for anyone else, but this was true of school where I was from."

Woah woah woah. You trying to start a theory/experiment fight?

I'll just put in my 2 cents. Experiments are where all the cool action is at.

Also, scoreboard:

Nobel prize distribution (as of 2014). Theory: 30.75 prizes (28.7%) Experiment: 76.25 prizes (71.3%)

> Woah woah woah. You trying to start a theory/experiment fight?

Hahaha no. I'm an observational astronomer - Everyone hates us! I definitely fall on the experiment side of the argument.

> Nobel prize distribution (as of 2014). Theory: 30.75 prizes (28.7%) Experiment: 76.25 prizes (71.3%)

I didn't know that, that's pretty neat. Although I was talking more about how the perception is in the general science community (starting from high school onwards). Again, I can't say how true it is outside of where I live, because I haven't travelled much. But it definitely is true here from my experience.

That's probably about right, if a little too lopsided toward theory. Physics is empirical. We need hypotheses to test, but we should emphasize "test."

There are much fewer theorists compared to experimentalists.

That's surprising if true because it doesn't take much resources to become a theorist vs. an experimentalist. Usually a modern computer will do. An experimentalist is usually out >$1e6 to setup a novel lab.

I, too, have a feeling that in the 21st century theoretical physics (understood as mathematical, or computational, physics) is destined to replace experimental physics in all areas - except those that do not yet have an effective mathematical model to work with. (I do not know if String Theory can qualify as such.)

An experimentalism promises results while a theorist promises commentary. In terms of funding, typically a large sum is awarded for equipment and students, and the 1M is never given to theorists.

They don't typically give the Nobel for theory. For example, Einstein is best known for Relativity but his Nobel is actually for his experimental work on Brownian Motion.

(1) Einstein's Nobel citation specifically mentions his work on the photoelectric effect, not his work on Brownian motion; (2) his work on Brownian motion was theoretical, not experimental; (3) there have been many Nobels for theoretical work --- all three of the 2016 Laureates, and both the 2013 Laureates, to pick some recent examples.

Thank you. I meant to say Photoelectric Effect. I misremembered.

This is true for giants of the past, but modern theoretical physicians have no way of distinguishing themselves to the public at large. Meanwhile, experimental physics produce novel results that actually prove other people wrong. I don't think the above effect will continue for much longer, if it is still in effect at all for people doing work now.

Your comment seems to imply that you got into a physics PhD from a non physics background - is that the case? If so, how can one message you to chat more about it?

I don't know. For a writer looking for inspiration for a character, she doesn't seem to be doing a very good job relating to or understanding Lisa Randall.

It reminded me a bit of The Big Bang Theory.

> New York Times

Is this just a New Yorker-ism? If they're referring to NYT, I've never seen it formatted that way.

It's a New Yorker-ism, much like "coördinate".

I've been reading the New Yorker for years (though I feel they've become even more politically charged than usual within the past year and have since stopped) and was always irked by those damn diaereses.

It makes "oo" easier to parse as separate syllables, but English has a huge amount of non-phonetic words. Why does this get an exception?

Too bad recent discoveries rule out Dark Energy: https://news.ycombinator.com/item?id=12783631

So, this can read - The Phlogiston of a Theoretical Physicist.

> Too bad recent discoveries rule out Dark Energy: https://news.ycombinator.com/item?id=12783631

The methodology of that paper has been questioned by other researchers in the field[0]. Among other things, the paper claiming cosmic acceleration was not significant did not factor in constraints on cosmology from other types of observations (e.g., cosmic microwave background, baryon acoustic oscillations).

[0] https://arxiv.org/abs/1610.08972

That paper's abstract seems to be "We're not systemically wrong so we're not systemically wrong, ergo, the result shouldn't be interpreted as us being systemically wrong", without ever actually addressing the possibility that they're systemically wrong (eg that an unfounded assumption is in all of the models with the "correct" value), but I feel that the actual thrust is meant to be something about independent lines of investigation.

Could you elaborate a little more on what they're actually saying, since I don't seem to understand it?

In particular, where they show that their lines of investigation are actually decorrelated in terms of assumptions (ie, there can't be a common, systemic conceptual flaw in all of them), or that those assumptions are all included by the disagreeing model? Because otherwise, it seems a bald assertion that their assumptions are correct.

Regarding being systematically wrong, the rebuttal paper is essentially arguing that, by ignoring other cosmological measurements, the original study refuting acceleration is potentially falling prey to systematics. The other cosmological measurements that are typically used rely on completely different observing techniques and physical processes.

Baryon acoustic oscillations[0] (BAO) rely on there being a predicted characteristic length scale based on when the baryons and dark matter de-couple from each other. By measuring the large-scale distribution of galaxies you can measure this characteristic length.

The cosmic microwave background[1] (CMB) is looking at the redshifted thermal emission from the hot plasma which filled the Universe during its youth. The brightness fluctuations correspond to temperature fluctuations in the early Universe.

Both the BAO and CMB are sensitive to the energy content of the universe and the relative balance between baryonic matter, dark matter, and any dark energy. Examining the BAO signal as a function of time may provide constraints on the acceleration (if the characteristic length scale grows faster than expected from a non-accelerating universe, I believe). Additionally, the power spectrum of the cosmic microwave background is sensitive to the existence of dark energy[2, e.g., pg 24].

Because these three measurements (BAO, CMB, Type Ia supernovae) are looking at completely different things (characteristic separation between galaxies, temperature distribution of hot plasma when the universe was 380,000 years old, and apparent vs intrinsic brightness for a special class of supernovae) which can be linked back to cosmological model parameters, it is unlikely that the systematics of all three would conspire to provide a false signal of dark energy. So, using all three as simultaneous constraints makes it far less likely to be mislead by systematics inherent in a single one of those three datasets.

Another aspect of the rebuttal (which I don't really understand because I don't work on Type Ia supernovae) is that the N16 authors made an assumption for the luminosity-corrections of the Type Ia supernovae that could increase the derived luminosity; this would reduce any signal of acceleration. The authors of the rebuttal also argue that this is part of what resulted in the decreased significance found by N16.

So, from my understanding, the rebuttal is essentially arguing that N16 incorrectly computed the dark energy signal by using an incorrect correction to the Type Ia supernovae and by ignoring additional cosmological datasets.

[0] https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations

[1] https://en.wikipedia.org/wiki/Cosmic_microwave_background

[2] http://www.quantumfieldtheory.info/cmb.pdf

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