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Posted on: Origins of the Universe, Big Bang or No Bang.
at 11/24/2009 7:07pm

And yet, Harry, you refuse to answer the very simple points that speedfreak laid out in response to what you had said. ... more(+)

And yet, Harry, you refuse to answer the very simple points that speedfreak laid out in response to what you had said. He took the time to respond to your points - can't you do the same? close(-)

Posted on: Gravity wells?
at 11/19/2009 12:44pm

At the center of any realistic object (like the Earth) - with the sole exception of a black hole (which is entirely ... more(+)

At the center of any realistic object (like the Earth) - with the sole exception of a black hole (which is entirely concentrated in the center) - there is no gravity in the exact center, so there the gravitational well is completely flat.

This is a famous result of Newton's (later shown to also work in Einstein's gravitational theory): if you are inside a sphere whose density is only a function of radius (so each shell of the sphere has constant density), the only gravitational force you feel is due to the parts of the sphere interior to you. So if you are fifty miles from the Earth's center, you'll feel the gravitational pull from every part of the Earth which is interior to a sphere of radius fifty miles, and it'll be the same pull as if all that mass were in the center. But you won't feel any gravity from the parts of the Earth that are greater than fifty miles from the center, in any direction. So obviously if you're at the center, then there's nothing interior to you, and you can't be pulled by anything, so there's no gravity.

Think on that for a bit: I think it makes intuitive sense, but it's very, very profound. That should also explain exactly why the density profile matters - because you need to know, at each distance from the planet's center, how much mass there is interior to you, and that is determined by the density profile. close(-)

Posted on: Gravity wells?
at 11/18/2009 7:25pm

Hi ianke - It depends entirely on what kind of object you're talking about. In particular, it depends on the object's ... more(+)

Hi ianke - It depends entirely on what kind of object you're talking about. In particular, it depends on the object's density profile (that is, how its mass is distributed around it). If you have an object that's densest in the inner regions, then the slope of the gravitational well will be steeper inside the object than if the object is denser on the outside. But most objects we'd consider (like the Earth, or even the Sun) come in layers and have pretty non-trivial density profiles, so the slope of the well wouldn't be something as simple as being parabolic or flat or whatever in those regions. close(-)

Posted on: What is the tempeture in space ?
at 11/17/2009 12:58pm

The other thing (and this is an extension of your original question) is that even in pure, empty space - away from the ... more(+)

The other thing (and this is an extension of your original question) is that even in pure, empty space - away from the light of a nearby star like the Sun - there's a background temperature in space. In fact, it's 2.725 degrees Celsius above absolute zero. It comes from the so-called Cosmic Microwave Background - a stream of microwave photons coming from every direction, left over from some of the very earliest stages of the universe. close(-)

Posted on: Gravity's speed of propagation
at 11/14/2009 5:37pm

Not a problem c is fundamentally engrained in spacetime (rather than just being a consequence of electromagnetism), so ... more(+)

Not a problem c is fundamentally engrained in spacetime (rather than just being a consequence of electromagnetism), so it makes sense that gravity - an effect of spacetime - would propagate at that speed. close(-)

Commented on: Lack of Gravity Waves Puts Limits on Exotic Cosmology Theories
at 2009-08-19 23:19:02

They don't need to fly it near a black hole for the same reason we don't need to fly by a galaxy to observe its light - ... more(+)

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Commented on: What's the Biggest Known Planet?
at 2009-08-17 12:42:18

That wouldn't be the most useful - brown dwarfs and planets form in VERY different ways, and it would be problematic to ... more(+)

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Commented on: What's the Biggest Known Planet?
at 2009-08-17 12:42:17

That wouldn't be the most useful - brown dwarfs and planets form in VERY different ways, and it would be problematic to ... more(+)

 close(-)

Commented on: Mysterious Light Originates Near A Galaxy's Black Hole
at 2009-07-02 20:01:51

Interesting idea but it's not a theory - just a hypothesis, and a pretty wildly speculative one at that. Scientists ... more(+)

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Commented on: New Observations Suggest Mid-Size Black Holes Exist
at 2009-07-01 22:53:52

Well, first off, knowing they're there is a lot different from finding them. The fact that they haven't been spotted, ... more(+)

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