Taking the Measure of Nothing in the Universe

By Corey S. Powell | January 31, 2017 11:43 pm
The universe bristles with structure on all scales. But really, it is all punctuated nothingness. (Image courtesy of Cryhavoc)

The universe bristles with structure on all scales. But really, it is all just punctuated nothingness. (Image courtesy of Cryhavoc)

Lately, I’ve been thinking a lot about nothing. Not just because focusing on nothing is a helpful, meditative antidote to obsessing over the recent barrage of anxiety-inducing news, but also because nothing is the most common thing in nature. After all, the overwhelming majority of the universe is not stars and planets; it is empty space. But empty space is not really truly completely empty. That’s what makes nothing interesting: Some places have a lot more of nothing than others, and even the emptiest places—the ones with the most nothing, you might say—still contain something. In fact, trying to figure out the nature of that something is one of the biggest unsolved issues in science.

Sorry. It does all start to sound rather mad after a while. I’ll back up and do some some explaining.

What started me down this path was a question on the site Quora: “If I went up into space, opened a jar for a few seconds, put the lid on tightly, and then came back down to my kitchen, what would be in the jar?” It’s a great thought experiment. Take a jar-size sample of different parts of the universe. What would you find inside it?

To simplify things, let’s make the “jar” a one-liter soda bottle. That’s a familiar standard size, and one that converts easily to other units. It’s 1,000 cubic centimeters, or 1/1,000th of a cubic meter, or more Pepsi than anyone should drink in one day. Now let’s start to break down the question. What’s inside a one-liter volume of “empty” space? The answer varies enormously depending on where you are. Space around low-Earth orbit is a lot different than space in some random spot between the planets, which is a lot different than the space between galaxies. To come up with a truly universal answer, I’ll do the only sensible thing and look at the universe as a whole—that is, the average density of everything we can see.

If you average out the entire cosmos, there is a total mass density of 9.9 x 10-30 grams per cubic centimeter, which is equivalent to 5.9 protons per cubic meter. Note that I was describing mass density, however, not particle density. According to the latest data from the Planck satellite, only 4.8 percent of that density consists of ordinary matter, mostly hydrogen nuclei (protons). On average, then, there is 0.3 atoms per cubic meter of space. Put in more normal terms, if you marked out a random cubic meter of empty universe, there’s a 2 out of 3 chance you would have no atoms in it. Within your one-liter bottle, you have an average of 0.0003 atoms, which is to say that there’s about a 2,999 out of 3,000 chance that your bottle is atom-free.

Better cork it quick. You don't want the universe to get out.

Better cork that bottle really quick. You don’t want any of the universe to get out.

Then comes the dark stuff, the invisible entities that account for the other 95.2 percent of the cosmic mass density. First off, there is dark matter. We have no idea what it is. The standard theory is that it is some kind of undiscovered particle, but there are more exotic possibilities, including new kinds of fields that modify the force of gravity. According to the current interpretation, 25.8 percent of the matter density is dark…stuff. Since we know nothing about the mass of dark-matter particles (assuming they really do exist), all we can say is that, on average, you’d have about 2.6 x 10-27 grams of dark something-or-other in your bottle.

Next up, dark energy. Remember when I just told you we don’t know what dark matter is? Well, we really don’t know what dark energy is. The only thing we know is that there is some kind of energy smeared through empty space; astronomers can tell it’s there, because the energy is pushing the universe apart, causing the cosmic expansion to accelerate. Weirdly, we don’t know what it is but we have a very accurate measurement of how much of it there is: 69.4 percent of the total density of the universe. (Energy and mass are equivalent, following the equation e=mc2, and there is so much dark energy that it “outweighs” all of the matter.) That means you’d have about 6.9 x 10-27 grams of dark energy lurking in your bottle.

But wait—there’s more!

The universe is not just matter and mass. There are also particles of light and other forms of electromagnetic radiation, collectively known as photons. A lot of them, in fact. There are about 450 photons per cubic centimeter, or 450,000 of them in your bottle. I found that amazing when I crunched the numbers. Odds are, you don’t have even a single atom in your bottle, but you have nearly half a million photons. Even more amazing, most of those photons do not come from starlight. The overwhelming majority of the photons in the universe come from the cosmic microwave background—radiation left over from the Big Bang, 13.8 billion years ago. Despite their abundance, the amount of energy the microwave photons contribute is tiny. Add them all up and they are the equivalent of just 1/1,000th the mass of the atoms.

We still have one more component to go, another weird one. The universe is full of neutrinos, near-inert and near-massless particles that effortlessly penetrate ordinary matter. There’s quite a blast of them streaming from the sun; about 100 trillion of them pass through you every second. Take the big cosmic average again and there are about 330 neutrinos per cubic centimeter, or 330,000 of them in your bottle. Physicists have not yet been able to pin down the exact mass of those neutrinos. All we know for sure is that their total combined mass is very small, so small that it does not noticeably affect any of the observable properties of galaxies and the large-scale structure of the universe.

So that is the bit of universe in your one-liter jar: a bunch of photons and neutrinos that hardly add up to anything, a schmear of dark energy, an unknown smattering of dark matter, and probably no atoms at all. That’s just the average of the entire visible universe, however. What if we come closer to home?

Our crowded cosmic corner

Dark energy is (probably) the same everywhere, so there’s no need to recalculate. The density of dark matter close to Earth is very difficult to measure; I’ll ignore it here, too. But the matter density increases like crazy when you get closer to home. The space between the planets is filled with the solar wind, a steady flow of particles (mostly more protons—the universe really likes protons). At Earth’s distance from the sun, the density of the solar wind is 9 protons per cubic centimeter, or 9,000 of them in your 1-liter bottle. Even ignoring interplanetary dust, the “empty” space around Earth’s orbit has 25 million times the matter density of the average universe.

Come to low-Earth orbit and things get a whole lot more crowded. At an altitude of 400 kilometers (about 240 miles), where the International Space Station orbits, there is still a lot of wispy atmosphere blowing around. The matter density there varies quite a bit, but it is on the order of 10 quadrillion times the cosmic average. When you see photos of astronauts doing a spacewalk in orbit, it sure looks like they are floating around in a vacuum. By cosmic standards, though, they are plowing through a veritable fusillade of atmospheric atoms. The non-vacuum up there is dense enough, in fact, that atmospheric drag keeps pulling the station down, requiring regular orbital boosts. It’s all relative.

Return to sea level where you are now, more or less, and you need to recalibrate significantly again. The density of Earth’s atmosphere at the ground is about 0.0012 grams per cubic centimeter. That is a factor of a trillion higher than what it is in low-Earth orbit. More to the point, it is 2 x 1027 times the average matter density of the universe. You could call that two octillion, or you could write it out: You are breathing a bit of universe that has been concentrated by a factor of 2,000,000,000,000,000,000,000,000,000. Your body is another factor of 1,000 denser still.

The extreme dynamic range of density is what gives the universe order. The exceedingly low density out there, between the galaxies, is what makes space transparent, allowing us to see nearly all the way to the outer limits of cosmic expansion. The staggeringly high density down here is what concentrates enough matter and energy to make life possible. And the organizing factor that gave rise to those the vastly varying structures is simplicity itself. It is just the pull of gravity, slowly but relentlessly amplifying little lumps and clumps. Give gravity enough time and those clumps turn into planets, atmospheres, and eventually people.

Follow me on Twitter for the latest science news and discoveries: @coreyspowell

The history of the universe is fundamentally about gravity creating dense patches of dense matter surrounded by enormous rarefied voids. (Credit: ESA)

The history of the universe is fundamentally about gravity creating dense patches of matter surrounded by enormous rarefied voids. (Credit: ESA)

MORE ABOUT: Big Bang, nothing, Quora
  • OWilson

    Great stuff!

    I posted a similar comment on another blog about the contents of a cubic foot of space in front of you in a typical living room!

    In addition to all the wonderful things you mention that are contained in this “nothing”, there is an infinity of electromagnetic radiation and fields from every part of space, and every electrical device on earth.

    This tiny space contains an infinite universe of it’s own.

    A humbling thought!

  • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

    Nice. Perhaps the universe exists to eventually understand itself despite a fetish for irony, then BOOM! It will be a near thing, illumination versus a Vogon Constructor Fleet, with religion taking the Vogon side as a test of faith.

    The safe path is North America pre-1492, “mostly harmless.” That future lacks computation. Meat alone is too coarse a mesh and too slow a traveler.

  • https://ridingtheirownmelting.wordpress.com/ cgs

    Very interesting post. I linked to this at the Science Channel at Disqus.

    Your comments on the density range of the universe reminded me of the fact that the size of a human on a log scale, is half way between the smallest things in the universe and the largest. The diagram below helps to visualize this:


  • Jorge Alfonso Echavarria Gutié

    That’s really cool. But I would like to know what could happen if I open the bottle in my kitchen. Would it blow? My intuition tells me I would at least hear a boom. Not a simple pop like when you open a jar of pickles, but something way louder. How much energy would it release?

    • Corey S Powell

      Well, a bottle like the one in the photo would probably leak like mad (if you were lucky) or shatter and implode (if not) when you brought it down to sea level. I don’t recommend the experiment!

      • Prof Quill

        Depends if that is a plastic bottle or glass. First of all, the difference between a true perfect vacuum, the density of space, and the composition of space at the ISS level is hardly significant given the 14.7 pounds per square inch on Earth.

        A plastic bottle will simply collapse upon itself, heck you can do that with your mouth. A glass bottle, on the other hand, I don’t think would have any problem containing the ‘vacuum’, take the opposite and imagine about 15 PSI and that’s like nothing. Your car tires are at least double that, probably a shaken beer bottle too.

        As far as opening it, I don’t think it would be any particularly big deal, just a ‘swoosh’ as air rushed in. I also think it would hold the vacuum fairly well, over time the seal will let stuff leak in but its not a big pressure difference.

        All of this not very scientific, just getting a feel as to how much 15 PSI (negative or positive) really is.

        • Corey S Powell

          Thanks. My thinking was that the specific type of bottle I illustrated — a long-neck glass bottle — would be susceptible to shattering because of the uneven distribution of pressure. I’ve seen lab mishaps when vacuum pumps were applied to inappropriate vessels. But if you have more specific insights I’d be curious to hear them.

  • dvt

    What if we literally shake that bottle really hard?

  • Mick Fummerton

    How much density is in the non observable photons sence the Big Bang? Is this Dark Energy?

  • Robert Kolker

    photons in a bottle, going at light speed and banging into the glass. What becomes of them?

  • joseph2237

    Zero has been a problem for mathematician for thousand of years. Today we know there is no such thing as Zero. Zero to infinity is meaningless because the zero is “in” a container which is not a zero. The container is a Fractal in which all things exist and is self sustaining. The Fractal is the same inside or out and is the nature of the Universe. So the jar in the article is a Fractal within the Fractal and like a circle we can’t determine where one end meets the other begins because they are infinite. The good news is, what works in one part of a Fractal works in all levels, layers, and sections. For instance all our physics laws have given us some control over our physical world and we are searching for more. The problem with Fractals is knowing how to get from a lower Fractal to a higher one. Going from the railroad to the second barrier required the application of many disciplines and going from one galaxy to another will require the application of many disciplines some still not known.

  • aepling12

    The Jar would contain air. At 12 lbs of pressure per square inch on vacuum inside the glass jar, it would shatter and allow normal atmospheric air at sea level to rush in on the implosion. You didn’t say “bottle” in the question and I assumed a normal glass jar.

  • Joffan

    Of course the dark matter, dark energy, neutrinos and photons won’t actually stay in your jar as you bring it down into your kitchen. Alternatively if you can make bottle that does confine dark matter, there’s a couple of Nobel prizes with your name on them just waiting.

  • FSinibaldi

    La voix des sens.
    ( last version )

    Dans la nature
    des sourires,
    et dans l’aube
    de l’espoir qui
    dépeint le matin,
    une image s’évanouit
    en créant le profil
    de la prairie silencieuse
    qui chante la tristesse
    et puis donne le
    soupir d’un moineau
    solitaire: je voudrais
    la lumière pour décrire
    la jeunesse d’un
    rayon fugitif…

    Francesco Sinibaldi


Out There

Notes from the far edge of space, astronomy, and physics.

About Corey S. Powell

Corey S. Powell is DISCOVER's Editor at Large and former Editor in Chief. Previously he has sat on the board of editors of Scientific American, taught science journalism at NYU, and been fired from NASA. Corey is the author of "20 Ways the World Could End," one of the first doomsday manuals, and "God in the Equation," an examination of the spiritual impulse in modern cosmology. He lives in Brooklyn, under nearly starless skies.


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