9
$\begingroup$

Almost the same as my other question but it isn't about how the universe would form.

What would happen if to the universe if someone changed the strength of gravity by say 2%?

$\endgroup$
  • $\begingroup$ So this is talking about changing the gravitational strength in an already existing universe? How rapidly does it change? $\endgroup$ – Tim B Oct 22 '14 at 8:21
  • $\begingroup$ @TimB Immediately in our universe $\endgroup$ – Beta Decay Oct 22 '14 at 9:55
  • $\begingroup$ What is the difference ? $\endgroup$ – Vincent Oct 23 '14 at 15:32
  • $\begingroup$ @Vincent This one is about what would happen if it changed now, the other's about the formation of the universe. $\endgroup$ – Beta Decay Oct 23 '14 at 16:02
  • $\begingroup$ Ummm....2% more black holes? $\endgroup$ – JDSweetBeat Mar 19 '15 at 14:03
4
$\begingroup$

Everything would become slightly heavier. 2% isn't enough to make huge changes, although birds would find it harder to fly. Buildings would be slightly weaker and fall more easily. Trips and falls would become slightly more dangerous, etc. Most buildings, supports, etc we make have far more than 2% redundancy so they would not start collapsing as a result of this change.

This would have interesting effects on the orbit of planets though. Suddenly planets are not moving fast enough to maintain their current orbit, that will cause them to fall in towards the sun until they gain enough speed and settle into a new orbit. The new orbit would almost certainly be both more eccentric than the previous one and shorter, the length of the year would change.

Equally the moon would shift into an eccentric orbit, and tides would grow stronger. The faster orbit of the moon would also break the tidal lock, causing it to no longer always point one face towards the earth. Over time that would correct but the correction would not be instant.

$\endgroup$
  • $\begingroup$ Your assumptions are valid only if gravity suddenly increased. If it was 2% from the very beginning (Big Bang), your answer is invalid and @John Meacham answer has better explanation of the consequences. $\endgroup$ – Peter M. - stands for Monica Oct 25 '14 at 0:29
  • $\begingroup$ @PeterMasiar yes. I asked that specific question in the comments on the question though... $\endgroup$ – Tim B Oct 25 '14 at 1:15
14
$\begingroup$

Things would be extremely bad, for large values of extreme.

Stars are a balancing act of external radiation pressure exactly counteracting the gravitational attractive force. By increasing gravity stars suddenly have 2% more gravitational potential energy they need to shed to regain equilibrium. How much energy is that? The gravitational potential energy of the Sun is 1041 Joules. Or roughly the same energy as would be released if the entire Earth were to be anhiliated with anti-matter. 2% of that is huge and it suddenly appears out of nowhere. So, very quickly the Sun has to shed about 10,000 times its yearly energy output. Life is certainly not going to survive that, but this happens for every star in the galaxy. Many, many will jumpstart to a higher order of fusion at the massive sudden increase in pressure and temperature, if they start iron-burning, you are in trouble.

Expect every supergiant to go supernova concurrently and many lesser stars to flare with the energy output comparable to a nova, any life that survives the semi-nova/flare of the Sun will be wiped out by the bombardment of gamma rays that will be bathing the Earth for the next few thousand years.

Every black hole will get a bit bigger all of a sudden as escape velocity increases, eating part of its accretion disk. Hard to say what effect this would have actually, but sounds like it may cause trouble.

Depending on exactly how the increase in gravity is carried out, even more esoteric things might happen. It is a well known unsolved problem in physics that the gravitational mass and inertial mass of matter are independent yet appear to always be exactly the same. As in, there are no laws that say they should be the same nor does it naturally arise from any currently accepted theories, but observationally it is always the case that they are identical to the limits of measurement. It is a good thing too as the exact correspondence between gravitational and inertial mass makes a lot of things like having stable orbits work. If you were to increase gravity by increasing gravitational mass and not inertial mass, suddenly things like angular momentum and stable orbits get all sorts of wonky. It is hard to say if solar systems are even possible in such a case.

All in all, it is a bad idea. Unless you are an energy being that really wants the universe to end in a Big Crunch instead of a Big Chill in which case crank up that constant, but expect biological life to take exception.

$\endgroup$
  • $\begingroup$ Great answer! And welcome to the site! But just so you know, we generally want answers to have a little evidence backing them up. We allow you to even cite Wikipedia (gasp) on this site. But we do appreciate something, or are these just speculations? Anyway, glad to have you here! $\endgroup$ – DonyorM Oct 23 '14 at 6:52
  • 2
    $\begingroup$ It is mostly fermi estimation, but the numbers are so huge, a few orders of magnitude it isn't going to change things much. :) calculating gravitational energy: burro.astr.cwru.edu/Academics/Astr221/StarPhys/gravity.html confirmed with entries here en.wikipedia.org/wiki/Orders_of_magnitude_(energy) reference on different types of mass en.wikipedia.org/wiki/Mass#Inertial_vs._gravitational_mass I think i am underestimating the damage caused to stars actually, so was very conservative in saying there would "just" be supernovas :) $\endgroup$ – John Meacham Oct 23 '14 at 6:56
  • $\begingroup$ You care right, I was considering the effects on planets and orbits but not on the internals of stars. It would need some pretty heavy simulations to model that but you're right that the results could be extremely dramatic. (although less dramatic results are also possible) $\endgroup$ – Tim B Oct 23 '14 at 11:33
  • $\begingroup$ I am not sure why this superior answer is criticized for lack of evidence when accepted answer does not provide any. $\endgroup$ – Peter M. - stands for Monica Oct 25 '14 at 0:27
  • 1
    $\begingroup$ @PeterMasiar I agree that this answer raised an extremely important point that mine had not considered. However stronger claims require stronger evidence. Most buildings on earth have extra strength designed in, the effect on the orbits is fairly easy to visualise. The effect on a star though is much harder to anticipate and a claim as strong as instant nova needs backing up in some way. $\endgroup$ – Tim B Oct 25 '14 at 6:23

Not the answer you're looking for? Browse other questions tagged or ask your own question.