How much dark matter passes through our body?
What if we told you that, One of the most mysterious and abundant substances in our universe
is passing through our body every second. You might have guessed it by now and
yes it's Dark Matter! The reality that we see today– planets, stars, galaxies etc,
make only 5% of the entire universe. The rest is Dark Matter and Dark Energy. And
it is passing through our bodies constantly. But how much? Does it have any effect on us?
We will answer these questions and more in this video!
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Our universe, despite all the planets, galaxies, stars and more doesn’t quite add up. If we look at
our Galaxy, The Milky Way, it doesn't have enough mass to hold all star systems together in the form
of a spiral galaxy? But still it does, How so? The same happens at the largest of scales, we find the
same story everywhere we look. There isn’t enough matter to account for the gravitational effects
that we observe. So what might be causing the stars and planets in galaxies to stick together?
To answer this scientists came up with the term- Dark Matter.
‘Dark’ because we cannot see it, we are just able to observe its effects. It is dark,
which means it is not visible in the form of stars and planets. Observations show that the universe
contains far too little visible matter to account for the 27 percent required by the observations.
Second, it is not in the form of dark clouds of ordinary matter, which is composed of particles
known as baryons. We know this because we can detect baryonic clouds by measuring
the absorption of radiation passing through them and we have found that it doesn’t react with any
electromagnetic radiation. Third, dark matter is not antimatter because we do not see the
distinctive gamma rays produced when antimatter collides with matter. Today we know that Dark
matter is present in almost all galaxies, and is the explanation for the hidden matter in galaxies.
We have confirmed the presence of Dark matter by a process called gravitational lensing.
Since Astronomers cannot directly see Dark Matter, they detect its presence by observing
how the gravity of massive galaxy clusters with a large amount of dark matter, bends and distorts
the light of more distant galaxies located behind them. Matter clumps together forming large
galaxies, large galaxy clusters and eventually us. Without dark matter we wouldn’t be here. Without
the presence of about five times as much matter as protons, neutrons, and electrons can account for,
none of this would be possible. Our Universe requires dark matter for proper functioning.
And if Dark matter is real, that means our milky way also has a Dark matter halo, and some of that
matter should pass through the Solar System, earth and even you. But how much? Let’s take a look.
In the early universe, everything was hot, dense and more uniform than it is today. Back in the
young Universe, everything was hotter, denser, and more uniform than it is today. Early on,
there were areas of slightly higher-than-average density, indicating a greater-than-average
amount of matter. Gravitation works to attract more matter into such a region,
but radiation pushes that matter back out. If only normal matter and its constituent
particles were to go with this radiation, the galaxies and galaxy clusters that we see
today would be extremely different from what we observe today. If all we had was normal matter
and its constituent particles to go with this radiation, the galaxies and galaxy clusters that
exist today would be vastly different from what we observe. Dark matter implies that every large
structure in our universe, such as a galaxy or a galaxy cluster, will be surrounded by a large,
diffuse halo of dark matter. Normal matter will congregate in the inner reaches of each galaxy,
because normal matter can collide and interact with both itself and radiation.
Dark matter, on the other hand, simply passes through everything: itself, normal matter,
photons, and so on. Dark Matter particles have no way to lose the large momentum they start off
with and only interact gravitationally. Each dark matter particle may have passed through
the galactic center only a dozen times till the present day in the entire history of our Universe.
On the largest of scales, the Universe is dominated by Dark Matter. But where we live,
just 25,000 light years from the center of the Milky way, normal matter is more dominant than
Dark matter. That situation is considerably worse here on Earth, in our Solar System, than it is in
interstellar space. The density of a human being is equivalent to that of water: 1000 kilogrammes
per cubic meter (kg/m3). If we take a look at the most realistic simulations that we can come
up with, the local density of Dark matter where we are is even less: about 10-21 kg/m3. If we added
up all the dark matter within all the people on Earth at any given time, it would amount to less
than a single nanogram. If you added up all the dark matter in the Solar System, all the way out
to Neptune's orbit, it would only amount to around 1017 kilograms: the mass of a moderately big
asteroid. And because it doesn’t have interactions like normal matter, it doesn’t move with the solar
system. Not only that, it doesn’t orbit the sun, doesn’t stay in a plane, doesn’t move
around the other stars or the galactic center, or even revolve around the Milky Way’s disk.
Simply put, Dark Matter moves under the influence of gravity, relative to earth at very high speeds!
In other words, this matter moves under the influence of gravity,
relative to Earth, at pretty rapid speeds! If you want to know how much dark matter
passes through you in a given amount of time, all you need are four numbers that
you can multiply together. They are: 1. the density of dark matter,
2. the surface area of a human being that the dark matter can hit,
3. the speed of the dark matter, 4. and the amount of time you
want to know the answer for. Once we've estimated the dark
matter density — and we already have it, at 10-21 kg/m3 — we can get the answer right away.
The surface area of a typical human is 1.7 square meters. Since the dark matter
comes in at a random angle, we can do a quick calculation and find a good estimate for the
area the dark matter "sees" is more like 0.6 m2. Our Solar System orbits the galactic center at
speeds of around 200 km/s, but infalling dark matter should be moving relatively quicker:
closer to 350 km/s. All told, that means dark matter moves, relative to a
human on Earth, at a speed of around 400 km/s. And we can do this for whatever times we want:
every second, over the course of a year, or over a typical (80 year) human lifetime.
Even though, at any given instant, there's only around 10-22 kilograms of dark matter inside you,
much larger amounts are constantly passing through you.
Every second, you'll experience about 2.5 × 10-16 kilograms of
dark matter passing through your body. Every year, approximately 10-8 kilograms
of dark matter move through you. And over the course of a human lifetime,
a total of just under 1 milligram of dark matter has passed through you.
What might seem like a minuscule amount really does add up over a long enough period of time.
The fact that these numbers are as large as they are not only teaches us something
about our bodies and what's in them, but how we might dream of searching for dark matter.
Whether it's made of extraordinarily low-mass or high-mass particles, we know the amount of dark
matter mass that passes through not just a human, but any detector of a given volume. If we presume
to know the mass of dark matter, we can calculate the number of particles that go through anything.
For decades, now, we've been building larger and more sensitive detectors, attempting to
probe whatever minuscule interactions might exist between dark matter and normal matter.
The most advanced detectors today use atoms with large nuclei in extremely large masses,
looking for signs of a recoil or other interaction. And so far, all the direct
detection techniques have come up empty. Dark matter, to the best of our knowledge, is out
there in all directions. It may be invisible to our eyes, but we can feel its gravitational force.
It passes through all the matter in the Universe, including human beings,
as though it weren't there at all. There are, to the best of our knowledge,
no collisions or interactions other than its effects on curving spacetime.
It doesn't clump, cluster, or form structure like dark atoms or molecules.
And yet, if it has even the tiniest hint of an ability to collide with either normal
matter or radiation, we'll be able to detect it. Over the course of your life,
about a milligram of dark matter will have passed through your body. If even one dark matter
particle interacts with one proton or electron in your body, we'll have a chance. When it comes
to dark matter — one of the Universe's deepest mysteries — it's hard to ask for anything more.