Universe not fat, just big-boned.

Researchers using NASA’s Chandra X-ray Observatory have discovered that the universe may weigh 10 to 20% less than previously estimated. It all stems from X-rays astronomers thought were emanating from heavy dust and gases between galaxies, but are actually more likely coming from relatively fit and trim photons and electrons. Less matter also means that there’s less dark matter, all of which adds up to a significant difference in the total weight of the universe.

When reached for comment, the universe expressed relief about finally having evidence that it is, in fact, a size 6.

All this made me wonder what the weight of the universe actually is, a question that does not appear to have occurred to Ken Than, the writer of the article floating around the Intertubes. Or, it occurred to him but he figured that everybody already knew. Or, maybe everybody does already know and I’m just pathetically ignorant of cosmological BMI.

I found this handy article at that tells me the universe did weigh approximately 100 trillion trillion trillion trillion metric tons. That was written well before this new discovery, so I suppose that means the new estimation is somewhere around 80 to 90 trillion trillion trillion trillion metric tons – which seems like a lot, I know, but really it’s all muscle.

Special thanks to my buddy John for tipping me off to the news and for giving me the size 6 joke. Please post your own universal weight-loss pun below.

Cross-posted at the SGU Blog.

Rebecca Watson

Rebecca is a writer, speaker, YouTube personality, and unrepentant science nerd. In addition to founding and continuing to run Skepchick, she hosts Quiz-o-Tron, a monthly science-themed quiz show and podcast that pits comedians against nerds. There is an asteroid named in her honor. Twitter @rebeccawatson Mastodon Instagram @actuallyrebeccawatson TikTok @actuallyrebeccawatson YouTube @rebeccawatson BlueSky

Related Articles


  1. Ugh. This is a prime example of a really really bad headline trying to say something that isn't in the paper at all. I'll copy-paste the comment I left on the blog I first read about this on:

    Glancing at the paper and guessing at how this could be butchered, it seems that they are saying, "if you assume that all of this gas is thermal (which in many cases it probably isn't), then you will mis-estimate the mass from X-rays." Mass of clusters aside (weak lensing measurements generally don't have 20% accuracy, and the Sunyaev-Zel'dovich effect is still gaining footing), the mass of the universe is well constrained from other techniques… nevermind that individual cluster masses can't tell you too much about the "mass of the universe" anyhow, but knowing the Hubble constant, that the universe is flat, and its age can constrain the total mass (within the horizon at least) fairly well.

    It's also worth a note that, while I've seen this headline plastered on several blogs over the last few days, I haven't heard a single astronomer mention it.

  2. Interesting Molliska, thanks.

    "I haven’t heard a single astronomer mention it."

    Yeah, I was wondering about that and wanted to ask Phil, but he's yet to respond to my chat thingy. I suppose it's early over there on the west coast, in Workfromhomeland.

  3. Well, the thing about the weight of the entire universe is that we really have no idea how big the entire universe is. There's still even a good possibility it's infinite in extent. The best we can do really is to figure out its density, put lower bounds on its size, and thus put a lower bound on its total mass.

    To follow up with Mollishka's comment, I think you nailed it right on there. All this paper really gets us the mass from the observable portion of clusters. We don't even need to adjust the total cluster mass from this (we just shift more of it into dark matter). Net effect on our calculations of the universe's density? Zero. We calculate that in an entirely different way.

    Oh, and here's you single astronomer mentioning it, in the comments at least. I might put up something on my blog about it if I can find the time today or soon.

  4. Okay, okay. So she may be a bit hefty. But isn't it more important that the Universe has a nice personality…? I mean, let's not be so superficial here! So what if she's a size eight as opposed to a size six? As long as the Universe feels good about herself, and can carry on an intelligent conversation.

  5. Rav Winston makes a good point. Hey, look, if the Universe is willing to crank out at least several billion kids and take care of a large number of them, who cares if she's a little hefty. Especially if she's still clinging to dolls, if you take my meaning.

  6. Well, at an age of approximately 15 billion, Mother Nature has earned the right to a few extra pounds anyway. The new figures just indicate that she needn't spend quite so much time at the gym anymore, and can have the occasional chocolate without feeling quite so guilty. Besides, true aficionados of the female form know that zaftig is healthier and more attractive than trying to be as skinny as a young universe.

  7. Ahem! That's only 13.7 billion, thank you very much. If you're going to incorrectly estimate a woman's age, be sure you err on the low side, or I won't be held accountable for the response.

  8. Hear, hear, Expatria. I'm just happy our universe has a few tiny corners where folks like us can exist and have the luxury of getting all angsty at times.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Back to top button