The Vast Emptiness of Space

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Space is empty.  There is nothing in a vacuum.  In space, no one can hear you scream (because there is nothing to transmit sound).  Well, sort of.  As it often turns out, what we are told is often a simplification of reality.  Space isn’t really empty.  It is full of things.  Space is just having less stuff in it than air, so we think of it as empty.  And, there is no such thing as a true vacuum. So, let’s move into the vast emptiness of space.

The Vast Emptiness of Space

To start with, let’s think of the outer space above Earth’s atmosphere.  The atmosphere doesn’t really have a sharp edge.  It just gets thinner and thinner.  There isn’t really a boundary between air and outer space.  We just arbitrarily define such an altitude.  The Space Telescope, and the International Space Station are actually flying through the Earth’s Thermosphere.  The air is so thin, that it can be mostly ignored, except for the tiny bit of drag that it produces, causing these bodies to slowly spiral downward.  Even farther out is the Exosphere. 

Beyond all semblance of Earth’s atmosphere, the planet’s magnetic field shepherds charged particles from the Sun into denser regions.  Even the Moon has a tiny amount of gas around it, hardly enough to really call an atmosphere, but more than nothing.

What is space filled with?

Well, you might think, if you get far enough from the planets, into interplanetary space, for example, then space will be empty, right?  No!  It turns out that the Solar System is filled with particles streaming from the Sun, called the Solar Wind.  Also, there are dust grains moving around the Sun.  Taken collectively, the interplanetary dust and gas are the interplanetary medium. 

The interplanetary dust has two sources:  comets bring it into the inner Solar System, and collisions between asteroids produce some of it.  These micrometeoroids are always impacting the Moon and orbiting satellites.  In fact, there is so much interplanetary dust out there that you can even see it from Earth!  Just after sunset or just before sunrise, look carefully at the twilight glow. 

What is Zodiacal Light?

Sometimes you can see a sort of pyramid of light extending from the glow along the horizon upwards along the ecliptic.  Most people miss out on this, thinking that it is more twilight glow.  Really, it is sunlight reflecting off of the interplanetary dust.  We call this the Zodiacal Light.  The best times to see the zodiacal light are when the ecliptic makes a steep angle with respect to the horizon.  This is after sunset in March and April, or before sunrise in September and October. 

The zodiacal light is faint, so you need to look when there is no moonlight interfering.  Also, it is often about as bright as the Milky Way, so if there is too much light pollution to see the Milky Way, then you can forget seeing the zodiacal light. 

Another way to see the interplanetary dust is to look directly opposite the Sun in the sky.  That doesn’t mean face some other direction when the Sun is up.  It means looking along the ecliptic, high in the sky at local midnight.  Sometimes you can see a very, very faint glow in the sky.  This is back reflection from interstellar dust farther from the Sun than Earth.  We call it the Gegenschein.  It is extremely faint, much more so than the zodiacal light.  Not only is it washed out by moonlight or light pollution, but it is even washed out by bright stars nearby, so it is very difficult to see.

So, what is the vast emptiness of space?

The space between the stars. Now that is the vast emptiness of space, right?  Nope.  Between the stars, you have what we call the interstellar medium.  For centuries, astronomers have seen nebulae through telescopes.  These vast clouds of gas and dust condense from the interstellar medium.  However, the fact that the interstellar medium was all pervasive did not really become accepted until the 1930’s when Robert Trumpler showed that the more distant a star cluster, the dimmer it appeared to be. 

Now, we expect that the more distant something is, the dimmer, but what Trumpler found was that the dimming was much greater than expected simply by the inverse square law of light.  His interpretation was that space was filled with a “fog” of sorts.  As it turns out, all through the galaxy, you find vast amounts of hydrogen and helium. 

Also Read: How did life begin on Earth?

These individual atoms and molecules add up.  There is more mass in the interstellar medium than there is in stars.  This interstellar medium is the source for new stars to form.  Eventually, it will run out, and star formation will cease (assuming that the galaxy isn’t stripped of its interstellar medium in a few billion years when it collides with the Andromeda Galaxy).

What about between the galaxies? 

There, you have the intergalactic medium.  The intergalactic medium is some leftover material from the formation of galaxies and galaxy clusters, but much of it is ejected from the galaxies themselves.  There is a galactic wind composed of material ejected largely by supernovae explosions.  Also, when galaxies collide, the interstellar medium is often stripped in part, or even almost totally, from the host galaxies.  This gas then is left between the galaxies. You find a very hot, energetic intergalactic medium in the big galaxy clusters where collisions between galaxies are very common.

Without any matter, space has force fields in it.  The gravitational and electromagnetic fields extend all the way through the universe.  They are everywhere.  Also, you have photons from the cosmic background radiation passing through all parts of the universe.  And, of course, light from countless stars and galaxies is passing through every point in space.

And, even if you ignore all of those things, space still isn’t empty.  Einstein showed us that matter can turn into energy.  However, the equation works both ways.  Energy can turn into matter, too.  Sufficient energy can create a particle and an anti-particle pair.  Every particle in the universe has a corresponding anti-particle.  When a particle and its anti-particle meet, they annihilate each other, and both are converted into energy. 

The Heisenberg Uncertainty Principle

But, here is the weird thing.  The Heisenberg Uncertainty Principle allows for a slight uncertainty in the time that the energy is released.  So, it is possible that the energy can be released a tiny fraction of a second before the particles meet.  But, with energy you can make particles, and again the Heisenberg principle allows for the particles to actually form a tiny fraction of a second before you use the energy. 

So, what can happen is that, in the vast emptiness of space, a particle and anti-particle suddenly come into being, and then annihilate each other, with the energy released being released early enough beforehand to be the energy that made the particles in the first place.  We call these virtual particles.  Space is filled with them.  Everywhere.  Vast numbers of them.  They suddenly pop into being and just as suddenly are gone.  Most of the time they are not around long enough to interact with anything.  Most of the time.  But, sometimes they do, so we have experimentally verified that these things do exist.

So, space isn’t empty.  In fact, space is very rich with structure and composition.  Just something to think about.

All the above information’s are collected from different sources on internet.

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