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In an infinite universe with random local density of matter, the gravitational constant would vary by location. Anyone know what the consensus is among astonom

In an infinite universe with random local density of matter, the gravitational constant would vary by location. Anyone know what the consensus is among astonomers if the universe is infinite or not ? Is there even a way to theoretically know ?

redis_mlc 5y ago
> In an infinite universe It's expanding now according to red-shift measurements. Whether that means it expands to infinity or collapses is unknown. > Is there even a way to theoretically know? Not directly, but if our red-shift, etc. measurements are only 13.8 billion years old, then either we're in the first universe, or it cycles. > the gravitational constant would vary by location Your gravitational constant question is a common one for non-physicists. The gravitational constant, G (aka "big G"), is a universal constant, which means it's a property of the gravitational force itself, not of density. Little g is the local gravitational acceleration, 9.81 m/s2 at the earth's surface. On the moon, it's 1.62 m/s2. You can read more here: https://en.wikipedia.org/wiki/Gravitational_constant https://en.wikipedia.org/wiki/Gravitational_constant To completely understand why G is needed, it's a scaling factor for our human-convenient measuring units for mass and distance. You could use alternate units that would make G = 1.0 if you wanted - called using "natural units" or "Planck units": https://en.wikipedia.org/wiki/Planck_units https://en.wikipedia.org/wiki/Planck_units I hope you enjoyed this physics lesson. :)
magicalhippo 5y ago
Theory can say what shape the universe should have, for example inflation predicts a flat universe[2]. Of course you then have to check if the theory matches what we observe. As far as I've gathered, the current measurements are consistent with a flat universe. Here's[1] a post about a recent, improved measurement. [1]: https://astrobites.org/2020/12/03/cosmic-clocks/ https://astrobites.org/2020/12/03/cosmic-clocks/ [2]: https://en.wikipedia.org/wiki/Flatness_problem#Inflation https://en.wikipedia.org/wiki/Flatness_problem#Inflation
naveen99 5y ago
Edit: cosmological constant, not gravitational constant

redis_mlc 5y ago

> In an infinite universe It's expanding now according to red-shift measurements. Whether that means it expands to infinity or collapses is unknown. > Is there even a way to theoretically know? Not directly, but if our red-shift, etc. measurements are only 13.8 billion years old, then either we're in the first universe, or it cycles. > the gravitational constant would vary by location Your gravitational constant question is a common one for non-physicists. The gravitational constant, G (aka "big G"), is a universal constant, which means it's a property of the gravitational force itself, not of density. Little g is the local gravitational acceleration, 9.81 m/s2 at the earth's surface. On the moon, it's 1.62 m/s2. You can read more here: https://en.wikipedia.org/wiki/Gravitational_constant https://en.wikipedia.org/wiki/Gravitational_constant To completely understand why G is needed, it's a scaling factor for our human-convenient measuring units for mass and distance. You could use alternate units that would make G = 1.0 if you wanted - called using "natural units" or "Planck units": https://en.wikipedia.org/wiki/Planck_units https://en.wikipedia.org/wiki/Planck_units I hope you enjoyed this physics lesson. :)

magicalhippo 5y ago

Theory can say what shape the universe should have, for example inflation predicts a flat universe[2]. Of course you then have to check if the theory matches what we observe. As far as I've gathered, the current measurements are consistent with a flat universe. Here's[1] a post about a recent, improved measurement. [1]: https://astrobites.org/2020/12/03/cosmic-clocks/ https://astrobites.org/2020/12/03/cosmic-clocks/ [2]: https://en.wikipedia.org/wiki/Flatness_problem#Inflation https://en.wikipedia.org/wiki/Flatness_problem#Inflation

naveen99 5y ago

Edit: cosmological constant, not gravitational constant