Question: What would happen if gravity timed by ten for five seconds then it went back to normal?

Daniel Williams answered on 3 Nov 2017:

So, lots of things would happen, and some of them are a bit weird. Assuming that the same thing happened all across the universe – with gravity becoming 10 times stronger everywhere, some of those things would be pretty scary.

First of all the orbits of the planets in the solar system would start to change, because the Sun would pull them 10 times harder towards it. Since the change only lasts for 5 seconds it probably wouldn’t be a very big effect, but it would be a permanent one, and the orbits would all be changed slightly.

Gravity’s an important force in lots of objects in the universe. If gravity was stronger it would make things heavier. That might cause some objects to crush themselves smaller. It’s sometimes quite hard to work out exactly what would happen in a situation like this, but we can make some approximations. The surface of the Earth would become 10 times heavier, and it would start to push down harder against all of the stuff inside the mantle and the core (the bits inside the planet). Those would be heavier too, and would start to push down on the core. I think we’d need to find a geologist (a person who studies rocks) to work this out properly, but this would start to cause earthquakes, and then as gravity went back to normal everything would start to relax again, making even more earthquakes.

Because the Moon would pull the oceans 10 times as hard it would start making a really big tide, but when gravity switched back to normal all the water which was being pulled would relax back, and that might cause tsunamis.

Stars exist because there’s a careful balancing-act in their core between gravity and pressure created as they “burn” their fuel (it’s not actually burned, but that’s a completely different topic!). If gravity became 10 times stronger the star would need to produce 10 times more pressure to stop itself collapsing-in on itself. It’s normally hard for a star to do this, and if it can’t manage this it would “implode” (that’s a sort of reverse explosion where everything goes inwards rather than outwards).

Our sun would probably collapse into a neutron star: that’s a super-dense object which is basically a giant atomic nucleus, about the size of a mountain. Most heavier stars would probably start to become black holes.

As it got crushed under its own weight Jupiter might start to become a star. I don’t know very much about how long it takes for this to happen though, and 5 seconds might not be long enough. However, the extra “crushing” pressure would be enough to heat it up so it could start using fuel the same way a star does.

I also think that because there was a sudden change in the gravitational field of lots of objects in the universe lots of gravitational waves would get produced too. Gravitational waves get produced any time a gravitational field changes shape. However, we don’t normally think about how gravitational waves would look from gravity changing rather than how objects move, so I’ll need to go away and think a bit harder about that!

Finally, there are things called gravitational lenses which are places in the universe where gravity distorts light because there are lots of heavy things near where it’s travelling. The sudden change in gravity would make these change the amount by which they distort light. However, because most gravitational lenses are far away, we would see this change at different times in the future for each of them, because it would take a while (thousands or millions of years) for the light to arrive at Earth. If we knew what time the change in gravity happened on the Earth we’d be able to work out very accurately how far away the lenses were by measuring the difference in time between when we saw the lens changing, and when gravity changed on Earth.