Hey, Vsauce. Michael here.
Gravity is a property of matter, anything with mass. This includes the Moon, Earth,
Jupiter, the Sun, and even you - your body. In fact, if you kinda like somebody, have
them stand 3/4 of a millimeter away from you. At that distance, cumulatively, every atom
in your body and every atom in their body will draw you two together with the same gravitational
force that the Sun is exerting on you right now.
Of course, we don't feel either of those forces because compared to the gravitational influence
of the Earth, they are basically nothing. You don't need to concern yourself with the gravitational
attraction between you and someone you're hugging, or, your individual body and the
Sun, 150 million kilometres away. In fact, the Sun may as well not exist.
What if the Sun disappeared?
Well, to be sure, it's not going to happen. The Sun will die billions of years from now
by expanding, boiling off our oceans and swallowing the Earth whole.
The Sun is not going to simply disappear. Matter and energy don't vanish. Of course,
matter can quantum tunnel to different locations, but on the scale of the Sun there is not
enough time in the lifetime of millions and billions of universes for such a probability
to even be worth discussing.
But let's discuss it anyway, as a thought experiment to determine how the Earth would
get along with no Sun. What will the Earth do and what can it do alone?
At the exact moment that the Sun disappeared, we would have no idea. Because it takes light
from the Sun 8 minutes and 20 seconds to reach Earth. So, for a little over 8 minutes
after the Sun disappeared, we would have no idea. Once we did, confusion and mass panic
would, most likely, ensue.
The Sun's gravitational grasp on our planet would also take 8 minutes and 20 seconds to
end. This is because gravity waves propagate at the speed of light. So, the very moment
we saw our Sun disappear, we would also lose its gravitational influence and Earth would
fly out in a straight line, tangent to wherever it was in its orbit.
The finite speed of light and gravity mean that as panic and fear spread across the Earth
at the loss of our Sun, we could still, for a while, look up into the sky and see our planetary
buddies, further out, continuing to operate as if nothing had happened.
For instance, Jupiter would continue orbiting and reflecting light from a Sun that no longer
existed for about 30 minutes after the Earth already knew the Sun was gone. And, depending
on where Jupiter was in its orbit, it would take another 30 minutes to an hour for us
to watch the reflected light of Jupiter snuff out.
With no moonlight or sunlight, the universe itself would be our only source of visible
light from space.
In 2004, Abdul Ahad calculated that the Milky Way contributes about as much light as 1/300th
of a full Moon. So there would be enough light from space for us to see around a bit. But,
of course, electricity and fossil fuels would still be usable for a while. So, cities and
towns could continue to be lit by manmade sources, just like a typical night; except,
it would be night everywhere.
Photosynthesis would stop immediately, and this is huge. I had a great discussion about
this video with Henry from MinutePhysics, and the new channel MinuteEarth. If you're
not subscribed to MinuteEarth, you definitely should be.
In one of his episodes there, he mentions that 99.9% of the natural productivity on
Earth is done by photosynthesis, which requires the Sun. Without the Sun, plants would no
longer be able to inhale carbon dioxide and exhale life-sustaining oxygen.
But, don't worry. Collectively, all of us humans, all 7 billion of us, breathe in about
6 trillion kilos of oxygen every year. But our atmosphere contains a whopping quintillion
kilos of oxygen. So, even without photosynthesis, and, including all the other animals, and
insects, and microorganisms that consume oxygen, it would take us thousands of years to run
out.
The poor plants themselves would be much worse off. Without the Sun, most of them would
die within days or weeks. Except for large plants. Giants trees, for instance, contain
enough sugar for energy that they could technically live in the dark for years. Their problem
is going to be that the Earth will get quite cold. In fact, mighty trees would freeze to
death. Their blood, the water and sap inside of them, solidify way before they died of starvation.
Right now, with our Sun, the average surface temperature on Earth, hot places and cold
places, and different seasons all considered, is an arguably comfortable 14 to 15 degrees
Celsius.
Without the Sun to add energy, the Earth would radiate away heat exponentially, meaning
it would go fast at first and then happen more and more slowly. By the end of the first
week without the Sun, the average surface temperature across Earth would be freezing.
Zero Celsius, 32 degrees Fahrenheit. Now, temperature's like this happen all the time
on Earth, we're used to it. Panic and fear and looters and anarchy aside, for the first
few days or months, we could get by.
But by the end of the first year without the Sun, the average global surface temperature
would be -73 degrees Celsius, -100 Fahrenheit.
The best option, really, would be to move to geothermal areas like Yellowstone or Iceland.
These places would be the few safe havens for human life after the Sun. Nearly all life
on Earth exists because of, and is dependent upon, extraterrestrial energy: the Sun. But
the Earth produces its own heat. Despite floating in the coldness of space for billions of years,
down below the crust the Earth is quite warm.
20% of this warmth came from the fact that when the Earth formed, mass crushed so tightly
in the middle that the pressure liquified rock. The other 80% of Earth's internal heat
comes from that fact that deep in its core, radioactive elements decay, providing the
energy needed to keep the Earth's core at 5,000 degrees Celsius.
Anyone who failed to secure a position within one of these bastions of warmth, or, perhaps,
underground in a community warmed and powered by nuclear fuel, would likely be dead within
the first year of no Sun.
In the next 10 or 20 years things would start to get wet with dew. But not with glorious
water droplets. Instead, droplets of liquid air. The air would literally become cold enough
for the gasses that make it up to condense, or form clouds and precipitate, first as rain,
and then as it got colder and colder, eventually, as snow.
In Fritz Leiber's famous science-fiction short story "A Pail of Air," this has already happened.
The Earth was ripped away from the Sun, and, in order to survive, a family must go outdoors
in a special suit and scoop up a pale of just the oxygen snow, bring it back in, and place
it over a fire to warm and allow them to breathe.
A year or so after the sun disappeared, Earth's oceans will have frozen over. Ice all the
way across. But ice is less dense than liquid water, which means that ice floats. And ice
is a pretty decent insulator. So, for billions of years after the Sun disappeared, liquid
water could still exist at the bottom of our oceans, protected and insulated from space
by miles of ice above it, and warmed by vents on the ocean floor that spew water out, super
heated by Earth's interior.
This would continue on Earth for a very, very long time - Sun or no Sun. Instead of becoming
frozen and lifeless, extremophiles, like microbes, that live around hydrothermal vents deep in
the ocean, would be fine. They live deep in the ocean, far below the point where sunlight
can penetrate, and they make energy not through photosynthesis, but via chemosynthesis - converting
heat and methane and sulphur into the energy they need. They are then eaten by clams and
tubeworms.
Extremophiles deposit minerals back into the vents, meaning that their food chain is complete.
It's a circle. It's independent of the Sun. Earthlings like them would thrive if the Sun
were to disappear. They would live just fine without every knowing that the Sun was gone.
Or, honestly, without ever even knowing it existed in the first place.
It's amazing to think that life, here on Earth, all alone, flying through space with no Sun,
would kind of be fine. Far from becoming a frozen dead rock, or a boring dormant seed,
the Earth would be a spaceship, carrying living passengers with enough geothermal heat for
billions of years of life.
If the Sun disappeared, spaceship Earth would fly out in a straight line covering about
30 kilometres every single second. After just 1 billion years, it will have covered 900 quadrillion
kilometres or about 100,000 lightyears - a trip that could potentially take it all the way across
our galaxy, near thousands of stars. And nothing's to say it couldn't fall into orbit around one,
thaw out, and allow its still-living extremophiles to proliferate life on Earth all over again;
maybe one day developing life intelligent enough to uncover whatever is left of our
lives. Maybe they could even find this very video.
In which case, hi, uh, you're welcome
for this video about your planet's history and journey.
And, um, as always,
thanks for watching.