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 km 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, breath 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 5000 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 10-20 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 sulfer 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 km every single second. After just 1 billion years, it will have covered 900 quadrillion

km, 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.