Do you need to understand the detailed mathematics of general relativity to be a professional astronomer?

Question

Could I become an astronomer by understanding how to use the main results of general relativity such as cosmological redshift or would I need to understand the whole theory?

It's not very clear what you mean by "the whole theory", or what you mean by "professional astronomer". However (1) all the physical sciences use maths a great deal, and (2) Relativity is now routinely taught in undergraduate classes. It's not exceptionally difficult maths. — James K, Apr 13 '23 at 09:27
I know two people with PhD's in astrophysics who are plummers. Making a living as a professional astronomer is tough. — Greg Miller, Apr 13 '23 at 15:29
An astronomer maybe (i.e. someone who performs observations), but not e.g. an astrophysicist or cosmologist. — StephenG - Help Ukraine, Apr 13 '23 at 19:55
@JamesK Special Relativity is almost always a part of every physics undergraduate's curriculum. However, General Relativity is not. My university doesn't even have an undergraduate course on it. — Zachary Kennedy, Apr 13 '23 at 21:03

score 5 · Answer 1 · answered Apr 14 '23 at 02:27

I guess there are two related but distinct ways of thinking about this question: from a skills perspective (i.e. do you need a functional knowledge of general relativity to perform astronomy research?) and from a requirements perspective (i.e. do paths to becoming a professional astronomer require you to learn the subject?).

The answer to the latter will depend strongly on the institutions you attend. Assuming you work towards a bachelor's (and, in all likelihood, doctoral) degree in physics, astrophysics or astronomy, you may be required to take a full, in-depth class on general relativity at some point. I know of universities where that is the case, usually in their graduate programs. That said, it's not universal; as both an undergraduate (in astrophysics) and a graduate student (nominally in physics, doing research entirely in astronomy), I've been required to take classes that touched on portions of general relativity and adjacent topics but not a full-on GR class. These topics included gravitational time dilation, gravitational lensing and the Friedmann equations. So the answer to this interpretation of the question is a maybe. It depends on where you study.

Regarding the former way of couching the question: in the day-to-day process of research, in many subfields you can certainly get by without knowing much or any general relativity. For example, the majority of work in exoplanets, planetary science and the interstellar medium uses little to no GR. Whether or not you know how to derive the Schwarzschild metric will not make a difference. Frankly, even fields where you would expect GR to pop up on a regular basis won't necessitate a deeper knowledge of general relativity. Half of my research is in pulsars; the other half is in gravitational waves. Believe it or not, I personally have not had to invoke any deep relativity knowledge in a long while; I could, strictly speaking, get by without it and still do good science in my field. (Granted, I work in observational astronomy -- pulsar theorists usually aren't so lucky!)

That said: Knowing general relativity beyond just the surface-level topics I was required to study has certainly served me well because of the research I do. I understand linearizing the Einstein field equations; this is obviously crucial to understanding gravitational waves. I understand (sort of!) the relativistic effects in tight binary systems; this has helped me understand the various phenomena (e.g. the Shapiro and Einstein delays) that are accounted for under the hood, so to speak, of our pulsar timing software. Same goes for post-Keplerian parameters. I do think I'm a better scientist for it.

Could I keep button-pushing each day and succeed in astronomy research? Probably. Have I been required to learn more than these surface-level results, as opposed to the nitty-gritty retails? No. But, given the choice, should you learn more general relativity? This is opinion-based and so beyond the scope of the question, but honestly, I really think the answer is yes.

score 2 · Answer 2 · answered Apr 14 '23 at 01:25

No, but it depends on what you work on

For example if you work on building telescopes (e.g. Hubble Space Telescope, James Webb) then you don't need to know anything about Relativity.

Some topics might require some GR, although it's not that much. Examples are solar physics, exoplanet searches (since gravitational lensing is part of the methods used), and SETI. You don't need to know GR thoroughly, since you can just use the results that other people derived. Another example is cosmology. Modern cosmology is built on the Friedmann equations. Every cosmologist knows how to use these equations, but there's a good chance they don't know how to derive it.

At the other end there are topics where you need a thorough understanding of GR. Here's an example of such a paper. The first line of the abstract says it all: "We study thermodynamic properties and phase structures of topological black holes in Einstein theory with a Gauss-Bonnet term and a negative cosmological constant". Many (most?) astrophysicists will have no idea what "Gauss-Bonnet term" means, but if you want to work on this topic, you will of course need a thorough understanding of GR.

@planetmaker I assume you mean "cosmology"? It certainly does use GR, but not to the extent where you know it well (at least not for the subfields of cosmology I'm familiar with). — Allure, Apr 14 '23 at 06:57
no. I mean telemetry and communications with whatever satellite or space craft. The redshift due to Earth's gravitation in frequency compared to the satellites one in the communication frequency must be taken into account. It is not negligible. That's especially true for deep space where you want to use a very narrow bandwidth to limit power. — planetmaker, Apr 14 '23 at 08:50

uhoh · Answer 3 · 2023-04-14T02:53:17.387

Of course if you want to be involved in research directly related to GR effects, then YES, definitely!

You will of course need to demonstrate some degree of understanding in order to get through graduate school - pass exams and candidacy tests - and successfully obtain your Ph.D.

After that, you will certainly need to retain the basics of "what happens when".

You'll probably need to know how to calculate how far the position of one object appears to move when the light passes by a second massive object, what a Schwarzschild radius is, why gravitational waves "chirp", maybe some time dilation equations, at a minimum.

But even if you avoid GR in your research, you will still have teaching duties and some of your students will be frighteningly smart! If you end up having to teach a class that requires you cover General Relativity and you can put off the Math and do some and answer questions about it, depending on the country students will complain about you!

So if you keep your head low and avoid teaching anything beyond Astronomy 101 and choose a field of research that only needs a few simple GR equations for corrections, you may do just fine!

So if you can't understand the basics, then proceed AYOR¹!

AYOR:

This brought back memories of taking special and general relativity courses in grad school and getting stuck with a professor, for both courses, who was lazy, cancelled classes without warning and used lecture notes so old, obsolete and yellowed that they were brittle. So I bought books, but that was a black hole experience: all expended effort vanished without a trace. — Ed V, Apr 13 '23 at 21:27

Do you need to understand the detailed mathematics of general relativity to be a professional astronomer?

3 Answers3