Life's Little Mysteries

Why is space a vacuum?

black hole in space
Dark matter could consist of ancient black holes. (Image credit: Shutterstock)

Space is an almost perfect vacuum, full of cosmic voids. And in short, gravity is to blame. But to really understand the vacuum of our universe, we have to take a moment to understand what a vacuum really is — and what it's not.  

So, what is a vacuum, and why isn't space a true vacuum?

First, forget the vacuum cleaner as an analogy to the vacuum of space, Jackie Faherty, a senior scientist in the Department of Astrophysics at the American Museum of Natural History in New York City, told Live Science. The household cleaning machine effectively fills itself with dirt and dust sucked out of your carpet. (That is, the vacuum cleaner uses differential pressure to create suction. Suction cleaner might be a better name than vacuum cleaner). But the vacuum of space is the opposite. By definition, a vacuum is devoid of matter. Space is almost an absolute vacuum, not because of suction but because it's nearly empty. 

Related: What would happen if you shot a gun in space?

That emptiness results in an extremely low pressure. And while it's impossible to emulate the emptiness of space on Earth, scientists can create extremely low pressure environments called partial vacuums.

Even with the vacuum cleaner analogy out, "understanding the concept of the vacuum is almost foreign because it's so contradictory to how we exist, Faherty said. Our experience as humans is completely confined to a very dense, crowded and dynamic fraction of the universe. So, it can be hard for us to really understand nothingness or emptiness, she said. But in reality, what's normal for us on Earth, is actually rare in the context of the universe, the vast majority of which is nearly empty.  

Gravity is king

On average, space would still be pretty empty even if we didn’t have gravity. "There's just not a lot of stuff relative to the volume of the universe in which you put that stuff," according Caltech theoretical astrophysicist Cameron Hummels. The average density of the universe, according to NASA, is 5.9 protons (a positively charged subatomic particle) per cubic meter. But then gravity amplifies the emptiness in certain regions of the universe by causing the matter in the universe to congregate. 

Basically, any two objects with mass will be attracted to each other. That's gravity. Put another way, "matter likes to be around other matter," Faherty said. In space, gravity draws nearby objects closer together. Together their collective mass increases, and more mass means they can generate a stronger gravitational pull with which to draw even more matter into their cosmic clump. Mass increases, then gravitational pull, then mass. "It's a runaway effect," Hummels said.  

As these gravitational hot spots pull in nearby matter, the space between them is evacuated, creating what's known as a cosmic void, Hummels said. But the universe didn't start that way. After the Big Bang, the matter in the universe was dispersed more uniformly, "almost like a fog," he said. But over billions of years, gravity has gathered that matter into asteroids, planets, stars, solar systems and galaxies; and leaving between them the voids of interplanetary, interstellar and intergalactic space

But even the vacuum of space is not truly pure. Between galaxies, there's less than one atom in every cubic meter, meaning intergalactic space isn't completely empty.  It has far less matter, however, than any vacuum humans could simulate in a lab on Earth.

Meanwhile, "the universe keeps expanding," Faherty said, assuring that the cosmos will remain mostly vacant. "It sounds so lonely," she said.  

Editor's Note: This story was updated on Oct. 9 to correct the spelling of Cameron Hummels' name. 

Originally published on Live Science.

Donavyn Coffey
Live Science Contributor

Donavyn Coffey is a Kentucky-based health and environment journalist reporting on healthcare, food systems and anything you can CRISPR. Her work has appeared in Scientific American, Wired UK, Popular Science and Youth Today, among others. Donavyn was a Fulbright Fellow to Denmark where she studied  molecular nutrition and food policy.  She holds a bachelor's degree in biotechnology from the University of Kentucky and master's degrees in food technology from Aarhus University and journalism from New York University.

  • TorbjornLarsson
    The article discuss a classical vacuum in a cosmological setting, leaving out the properties of the quantum field vacuum (such as having fluctuations and so a temperature even without particles), but even so it simplifies the latter.

    "After the Big Bang, the matter in the universe was dispersed more uniformly, "almost like a fog," he said. But over billions of years, gravity has gathered that matter into asteroids, planets, stars, solar systems and galaxies; and leaving between them the voids of interplanetary, interstellar and intergalactic space."

    The hot big bang expansion era of itself can't produce a uniform - homogeneous and isotropic - universe analogous in that only sense to how unlikely it is an explosion would. That is the task for the preceding inflation era.

    Conversely, a flat normal matter filled universe can't produce the inhomogeneities and the matter content sufficient to gather the matter into galaxy clusters and galaxies. That is the one place where we have to inject the quantum field physics to, on the one hand have the 10^-5 parts energy fluctuations that during the later hot big bang transforms to fluctuations in gas density and momentum, on the other on the way of a universe cooling and giving normal matter somehow gives the 5 times more mass of dark matter. Without either of those components, without inflation fluctuations and hot big bang dark matter, we wouldn't have galaxies and the voids in between. instead it would just dilute with expansion.

    Expansion may sound lonely and cold, heading for the heat death of the universe, but it is what enabled evolution of life. It is in the heat death of the universe that it suffices to make a classical model without breaking too much of the mold. In the general relativistic universe the cosmic background photons gets stretched by the expansion, and the radiation temperature of the voids will tend towards 0 K. But in the classic thermodynamic model the interactions between particles (here, galaxies) will have a gravity potential energy which increase subtracts from the system kinetic energy and cools it as it expands.
    Reply
  • AlexS
    Why? Because that's the way the FSM (praise be to his noodly appendage) made it.
    Reply
  • TorbjornLarsson
    AlexS said:
    Why? Because that's the way the FSM (praise be to his noodly appendage) made it.

    Everyone knows LCDM beat out FSM because it is the longer acronym.

    No. no need to thank the scientists, facts (and Nobel Prizes) are their own reward! 👹
    Reply
  • dizzo
    When the Universe started to fall:
    The Gravitational Instability Cosmological Theory on the Formation of the Universe.
    The Theory:
    (1) The expansion of the universe is a result of the " heat ' contained therein;
    (2) The source of the " heat " is the cosmic microwave radiation background at 3 kelvin,
    wherein;
    (3) The microwave electro magnetic-nuclear energy was formed as a result of the
    interaction of two different static gravitational vacuum fields, causing gravitational
    instability and the motion, void of matter, at this time, wherein; static gravitational
    field (1) began to go into "motion".

    Therefore; the interaction of (2) motionless / static gravity vacuum fields, could eventually create dust particles in the Universe that later form into stars, galaxies , planets, moons and other objects in or about their current locations.


    Q: When did this motion start?
    A: If a neutral particle is able to resist the universal motion, in theory, that particle
    would go back in time. Going back in time the neutral particle would then enter into (1)
    of the (2) motionless-static gravity vacuum fields void of motion, and cause an unbalance
    and gravitational instability and this interaction would create motion and energy
    particles.
    Q: What causes a gravitational static vacuum field in the first place ?
    A: Pressure force is used to create a vacuum on Earth, perhaps an exotic something
    100,000 times weaker than the force of gravity decays, causing a static-motionless gravity vacuum field.

    Q: What created the motionless gravity vacuum fields in the first place ?

    A: Vacuums are created by pressure so the only answer I can think of is a created gravity vacuum pressure from the future goes back in time to start motion in the past.

    ( DRI Daniel Izzo 20_, theory needs improvement - help yourself )

    Is it possible people created a Higgs muon that started motion in the universe?

    Where is the center of the universe ?

    If people first started motion on earth, then wouldn't the earth be at the center of motion in the universe ?

    Attached is a Wikipedia photo of the comet ISon, *( 2012-2013 ) notice the redshift of light of the stars in the background....to me it does shift but in what direction ...the redshift of light means its moving away from Earth ?

    Notice the red shift of cosmic light in the back ground stars in the Comet Ison where are they pointing to and moving away from ? Is it the Earth ? why does it look that way ? Did people start motion here on Earth ?

    Can anyone point in the direction of the universe where the Big Bang occurred?

    Is it possible people created a Higgs muon that started motion in the universe? If motion first started on earth, it would explain why the cosmic red shift points to the earth at the center of the universe, maybe because motion first started here? see: ” The red shift hypothesis for quasars: Is the earth the center of the universe? - Astrophysics and Space Science August 1976. “ The recently generated Higgs boson muon experiment at LHC in Cern in 2012 ..the Higgs muon may have decayed faster than the speed of light as predicted.

    Could people have started motion in the universe by generating a particle that allegedly went faster than the speed of light ? (with a 10 Billion Dollar man made machine that is colder than the 3 kelvin universe vs the LHC at 2 kelvin and creating a particle that goes back into time - 15 billion + years ago, ) when there was no motion - just motionless static gravity fields and that particle started motion, (gravitational) instability, the microwave background was then formed as a result of the instability, that created dust particles and matter in the universe ?

    Was this the time the universe started to fall (expand) into another static gravity field past the microwave background ?

    When was the last time the universe was at 2 kelvin ?


    Did the Universe create itself as the late Steven Hawking alleges ? Aren't people part of that Universe ? Could it be all man made ? To me it looks like everything we see was created by people, or God like peoplefrom motionless fractals to the start of motion in the universe within in an absolute zero kelvin static gravity field . Notice the Blue shifted Andromeda Galaxy is heading towards the Earth - when you throw a stone in a pond of water it ripples out except the middle it heads towards the cast stone.displacement. From Wikipedia " The Andromeda Galaxy is moving toward our own Milky Way galaxy within the Local Group; thus, when observed from Earth, its light is undergoing a blueshift. " https://en.wikipedia.org/wiki/BlueshiftHiggs

    and the Faster-than-light neutrino anomaly at Cern https://en.wikipedia.org/wiki/Faster-than-light_neutrino_anomaly







    Can anyone point in the direction of the universe where the Big Bang occurred?
    Is it possible people created a Higgs muon that started motion in the universe? If motion first started on earth, it would explain why the cosmic red shift points to the earth at the center of the universe, maybe because motion first started here? see: ” The red shift hypothesis for quasars: Is the earth the center of the universe? - Astrophysics and Space Science August 1976. “ The recently generated Higgs boson muon experiment at LHC in Cern in 2012 ..the Higgs muon may have decayed faster than the speed of light as predicted.
    Could people have started motion in the universe by generating a particle that allegedly went faster than the speed of light ? (with a 10 Billion Dollar man made machine that is colder than the 3 kelvin universe vs the LHC at 2 kelvin and creating a particle that goes back into time - 15 billion + years ago, ) when there was no motion - just motionless static gravity fields and that particle started motion, (gravitational) instability, the microwave background was then formed as a result of the instability, that created dust particles and matter in the universe ?

    Was this the time the universe started to fall (expand) into another static gravity field past the microwave background ?

    When was the last time the universe was at 2 kelvin ?
    The Gravitational Instability Cosmological Theory on the Formation of the Universe
    When the Universe started to fall . When did Motion Start ?
    (1) The expansion of the universe is a result of the " heat ' contained therein;
    (2) The source of the " heat " is the cosmic microwave radiation background at 3 kelvin,
    wherein;
    (3) The microwave electro magnetic-nuclear energy was formed as a result of the
    interaction of two different static gravitational vacuum fields, causing gravitational
    instability and the motion, void of matter, at this time,

    wherein; static gravitational field (1) began to go into "motion".

    Therefore; the interaction of (2) motionless / static gravity vacuum fields, could eventually create dust particles in the Universe that later form into stars, galaxies , planets, moons and other objects in or about their current locations.

    When did motion first start ?

    Science knows the formation of matter in our universe was caused by the forces of the

    universe.

    These forces are:

    (1) The Force of Gravity

    (2) The Force of Electro Magnetism

    (3) The Strong Nuclear Force

    (4) The Weak Nuclear Force

    At some point in time, motion within the universe, had to begin.
    The paradox would be, what force could cause motion to begin, without moving in its
    present space-time ?

    The Gravitational Cosmological Theory was
    developed from an is rooted in the Einstein Steady State Theory and the Bondi-Gold-Hoyle Steady State Theory,

    Wherein the Steady State Theory the universe,
    contains more protons than electrons that
    create dust particles and
    galaxies formed in their current locations and the cosmic
    matter is recycled therein at the center of the galaxy furnace.
    Reply
  • John_with_a_B
    admin said:
    The nothingness of space is hard to wrap our heads around.

    Why is space a vacuum? : Read more

    I have long wondered what the temperature is inside a vessel that has no particles inside and is shielded from all electromagnetic radiation, including the cosmic background radiation. The phrase "Divide by Zero" crosses my mind...
    Reply
  • AmandaX
    What bothered me was the INCREDIBLELY outdated simplification you would tell a 5yr old that Gravity is objects with mass attracting one another (paraphrase). That’s just reckless reporting in a science article. That’s close to asserting the moon is made of cheese. Forget all the other half truths and mistakes in the article. One should not be writing this sort of article without some basic knowledge of astrophysics and what’s happening currently in the sciences. I award you no points and may Zod have mercy on your soul.
    Reply
  • David J Franks
    TorbjornLarsson said:
    "Expansion may sound lonely and cold, heading for the heat death of the universe,"
    There can be no such thing as a heat death. Matter- energy, motion and order has always existed in one form or another, even before our Big Bang. The fact a heat death hasn't occurred after an infinite time has passed means there never will be one! This can only be if there's a cyclic or recycling process at work.
    Reply