# Tag Info

2

In some models of quantum gravity there are 10 dimensions. 7 of these are curled up and very small. Gravity is a force it is not a dimension. If these models of quantum gravity is correct then we do live in these 10 dimension. If these models are correct then we do live in "hyperspace", but only 3 dimensions are macroscopic. Dimensions don't govern the ...

1

The two comments are correct. Lets assume there is an object of radius $R$ and mass $M$, from a Newtonian point of view, if you are at another radius $r$, such that $r > R$, then there is no difference in the gravitational field experience by an object at $r$ if the mass spread across a shell of radius $R$ or if its concentrated anywhere between $r=0$ ...

-6

If the speed of gravity is equal to the speed of light, which most conventional astronomers believe, our solar system would have evolved in a completely different way. The speed of gravity is a critical physical fact that tells us why the theory of General Relativity is an absurd hypothesis in the first place, close to pseudoscience. Isaac Newton assumed ...

10

Surface gravitational acceleration on an object with mass $M$ and radius $R$ is given by $$g = \frac{GM}{R^2} \propto G\rho R$$ where $\rho \propto M/R^3$ is the density of the object. Titan is larger than Earth's Moon, so it must be less dense. Wikipedia confirms: $R_\text{Titan} = 1.5 R_\text{Moon}$, but $\rho_\text{Moon} = 3.34\rm\,g/cm^3$ while ...

0

Edited. I thought about this wrong. A slowly spiraling in orbit would hit the earth at not much more than orbital speed, which is escape velocity over the square root of 2, but not a meteor approaching from a distance, so I thought about this the wrong way. Answer is no.

1

Upon some google-ing and wiki-ing I found this image of a gravity map of the moon: That scale up the top is measured in milli-Gal which is thousandths of a cm/s^2. For scale gravity is ~9.81m/s^2 which equals ~981000mGal. The difference between gravity at sea level and the top of mount everest is 2Gal, or 2000mGal, which is 0.2% of average gravity. On the ...

2

If you mean the escape velocity of the Earth, then no. Any meteor that enters the earth's atmosphere and burns up or collides with the earth must have had higher than the escape velocity, purely because they were not from that one body. Unless of course as you say they have ricocheted of another object in orbit sufficiently reducing the kinetic energy to ...

16

Planets and stars, no. Globular clusters and galaxies, yes. Small scales To condense into such relatively compact objects as planets, stars, and even the more diffuse star-forming clouds, particles need to be able to dissipate their energy. If they don't do this, their velocities prohibit them from forming anything. "Normal" particles, i.e. atoms, do this ...

3

I guess you are talking about black hole formation here. If we take the Oppenheimer-Snyder model for the spherically symmetric collapse of a star, then an event horizon forms first followed later by an apparent horizon that is at, or interior to, the event horizon. The event horizon is the surface behind which light rays will never reach an infinite ...

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