Getting locked up! (and more..)
This is a question that gets asked probably about once a month or so in person, and is sent in about twice a year or so.
What would happen if Earth were tidally locked with the Sun?
Also known as being in a synchronous rotation, in this scenario, the time it takes for Earth to make one complete rotation is equal to the time it takes to make one complete orbit around the Sun, or just over 365 current Earth days.
Temperature wise, not much would change. It would change eventually, and at a rate that’s substantial, but it wouldn’t become a desert with the dark side becoming an arctic snowstorm right away. Let’s assume for the moment that this happened overnight, omitting the pesky details of things like general physics throwing us at wild speeds at the sudden deceleration of Earth. The sun would continue to “rise”, but not in the way that it happens now. As the current year progresses, the path the Sun takes during the relative daytime that you’re reading this changes. Each day, it takes a slightly different straight line closer to one side of the horizon. We know this is called the solstices, but in a tidally locked situation, this would continue to happen. Only, the day time would take about a year to pass, and the Sun would travel North to South.
The actual temperature, would be roughly 20 degrees Celsius, across the globe (yes, including the dark side!). That wouldn’t last long however, as greenhouse gasses would get out of control quickly to the point where the Sun side would eventually get to about 250 degrees, or about what Venus is now. The dark side of the planet would be about -80 degrees Celsius, cooling more and more until it was about the opposite of whatever the average temperature worked out to be on the Sun side. Humanity would have to live along the fringes, for the short time that the planet was habitable.
Eventually, the planet would be uninhabitable, with wild temperature ranges, non-breathable atmosphere, and the inability to grow proper crops without substantial technology. If the atmosphere didn’t get us, the starvation would.
Since I accidentally hinted at another common question above, I might as well kill two birds with one stone here, and answer it..
What would happen if the Earth suddenly stopped spinning?
One of the most commonly overlooked parts of Physics is Inertia. While any science minded or physics educated person reading this is currently laughing at me, not everyone has a Doctorate. It’s nothing bad, you’re one of the many that consistently forget if you drop a basketball and cannonball at the same time on Earth, they will fall at the same speed and hit the ground at the same time. If Earth were to stop spinning instantaneously, then we’d have substantial world wide damage. The first problem would be that everyone and everything is currently used to the fact that the Earth is spinning at about 500 meters per second. All of a sudden, everything’s speed would now be accelerated to that, which for the most part, humans in their cars would then be slammed into the closest Eastern object, and most likely die. Humans walking, buildings, objects in air, all of a sudden are traveling East at 500m/s instantly. If the sudden inertial change didn’t destroy you, the object you’re now going to be intimate with, would.
But let’s say that you’re skydiving, there’s nothing for you to slam into, so we’re not worried about that. From your perspective, you’d still be falling at the same speed, but below you would be a blur. Earth would appear to be suddenly spinning so fast that everything on the surface is a blur. What’s actually happening though is you’re suddenly moving, not Earth. We’re forgetting something important though.. take a deep breath and think about what we’re forgetting.
That’s it! Air! Atmosphere! Well, that’s a thing that has momentum, and if Earth were to suddenly stop spinning, then the momentum of the atmosphere would then be hitting you.. at roughly 500m/s. That would pretty much tear your flesh from your bones. Lets say you’re resiliently tough, and managed to brush off this wind damage as a slight breeze. The sound of everything below you would create a consistent sonic boom explosion sound lasting until everything equalized itself and settled down.
You’re invincible though, and survived that too. What would life be like now that probably everything is dead or destroyed?
You’d die of starvation. Pretty much everything living on the Earth is now a fine pink paste. The Oceans would then get their chance of revenge at all the crap we’ve put into them. Tsunami’s are now traveling at 500m/s across all the land masses on the planet, washing away all the pink paste and debris. We’d likely see a complete change in the geography of Earth once that as well settled down. Gravity would continue to work just as it does now; you wouldn’t float away into space.