Physics Stack Exchange

By Sean Carroll | January 13, 2011 10:06 am

This is a fun thing to check out: the Physics Stack Exchange is a crowd-sourced approach to asking (and getting answers to) physics questions. (Hat tip to Chad.) Someone asks a question, others suggest answers, which then get voted up or down depending on how helpful they are perceived to be. It’s like an Urban Dictionary for Physics.

A quick peek around reveals that there are some really smart physicists answering questions there. See the FAQ for more details about how the system works. Note that it’s aimed at “active researchers, academics and students of physics.”

I know that I’ll be forwarding this site to people who email with physics questions. Which means that really I should contribute to answering some of them. You all should too!

  • Jason

    This family of sites is great, I use Stack Overflow all the time. Hopefully they don’t get overrun with crackpots who might see this as a way to push their special brand of crazy. The science forums I frequent always have ongoing threads with crackpots talking about an electric universe or tired light or how the surface of the sun is solid iron…

  • Mike

    It’s not solid iron?

  • David

    I’ve been a member of since near the beginning, and I just wanted to say thanks for the nice review. We’ve put a lot of work into trying to make the site a good place to get well-reasoned answers to interesting questions, and it hasn’t always been easy, so it’s pretty gratifying when someone with your expertise looks at it and likes what they see. And of course we’d be thrilled to have you and/or any of your readers on the site to ask and answer questions – the more the merrier! (@Jason: we’re trying to learn from the mistakes of science forums before us, and taking a strong stance against crackpot questions.)

  • Cosmonut

    Great link, Sean.
    I just posted a question there which may be of interest to readers of this forum.

  • Jess Riedel

    Can someone explain the difference between this and, which I think uses the same software?

    Shortly after StackOverflow came out, MathOverflow and PhysicsOverflow both appeared. MathOverflow has become a phenomenal site as they have managed to keep the level of questions very high so that the site is useful for researchers. PhysicsOverflow, on the other hand, is filled with homework questions and crackpots.

    Was simply started with a more reliable userbase? Does it have a different relationship with the rest of the StackExchange universe?

  • Shecky R.

    other sciences and math have such sites, and such collaborative endeavors are one of the most positive, productive uses of the Web

  • Jonathan Lubin

    I find MathOverflow much more addictive than Facebook, and what’s more, there’s no guilt involved!

  • David

    @Jess: when the people of Stack Overflow first decided to expand to other topics besides computers, they first created a system, Stack Exchange 1.0 which would allow anyone to create a site using what was, at the time, essentially the same software as Stack Overflow. Most of the sites created using that system never really took off, probably in part because maintenance and promotion were the sole responsibility of the individual site owners. (Math Overflow is a notable exception, because it happened to have a larger group of committed supporters from the beginning)

    At some point, the Stack Overflow team realized their system wasn’t working so well, so they called off SE 1.0 (leaving the existing sites in place, but blocking any new ones) and created a new system, Stack Exchange 2.0, in which sites would have to go through a community approval process to be created, presumably guaranteeing that they would have a critical mass of people right from the start. is one of these newer sites. It basically replaces Physics Overflow. All the sites in the SE 2.0 network have the support of the Stack Exchange team for site promotion and development to give them the best possible chance to succeed, and they’re kept up to date with all changes made to the software that underlies Stack Overflow (which was not the case for SE 1.0 sites).

  • Jeff

    I like the idea of a physics crowd-sourcing tool that is not overrun by crackpots, but I’m not sure I like the big banner that proclaims the site as “for active researchers, academics, and students of physics.” I am none of those (formerly all of those), but I would humbly protest that I am not a crackpot. I think it would be better to define the scope of the discussion in terms of the subject matter of that discussion (e.g., “no crackpottery”) and not in terms of the allowable range of participants. In other words, those of us with alternative physics lifestyles might actually have something useful to add to the discussion. :)

  • David

    wow, I really need to stop obsessively replying to this comment thread :) Jeff, thanks for pointing that out. I’ll bring it up at the meta-discussion site and we can probably get that changed. Anyway, that wording was never intended to imply that only certain people can participate! It was only meant to identify the primary target audience. The site is open to anyone, and each post gets judged as crackpottery or not on its own merits.

  • Joel Rice

    That is a neat site – just looked at ‘is angular momentum truely fundamental’ . Good stuff and Thanks.

  • Joe Fitzsimons

    I hope you don’t mind me plugging it here, but there is also a proposal for a Theoretical Physics StackExchange. The reason for this proposal is that the current Physics SE site operates at a level similar to the Math StackExchange, but there seems to be substantial interest in a site focused on research level questions, similar to MathOverflow or the Computer Science Theory StackExchange. The idea is to build a community where the questions and answers are useful to practicing physicists, rather than one dominated by pop sci and coursework level questions. This isn’t meant as a slight against the Physics SE, but rather a complimentary site in a similar way to the relationship between Math SE and MathOverflow.

    Anyway, if there are any physicists out there who have not joined, I would encourage you to. At the moment the site is fully through the definition stage and 38% of the way through the commit phase (where potential users are asked to sign up to answer or ask 10 or more questions with in the first 3 months of the site). This commitment isn’t really binding, its simply a way for the StackExchange folks to build a community before launching the beta so that there is a good userbase from day 1. At the moment (looking over the currently committed users) we are very strong on quantum information and a few other fields, but it would be a very good thing to have users from all areas of theoretical physics. If you are dubious about the potential for such a site, then I would encourage you to look at the CS Theory site (, which has rapidly become a fantastic resource for the computer science research community. So, if you think this might be a useful resource, please do come and sign up.


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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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