The unbearable lightness of being... Gravity.

[Jinx]

Surely +ve and -ve are purely arbitary and based on origin and direction. If Gravity is only +ve then it only means the origin is beyond our ken not that it doesn't exist (well doesn't exist in our cosmos but is outside of it - but not beyond it - think 3D to 2D ) ?

[Gene Vincent]

No, but I can see the thinking behind what you write.

But gravity is an accelerative effect on a body in attraction to another, that is a +ve effect.

A -ve gravity would have things either suspended in mid-air or zapping off in all directions.

We do see things zapping off in all directions, or rather we see things because Photons which are massless do precisely that, but even something so massless as a photon is swayed by gravity in its path and can be captured.

But gravity doesn't do this due to pulling on some unestimable mass, it does this by 'fooling' the Photon that its path has remained a straight one.

This is the true meaning of the warping of 'spacetime' the Photon sees no warping, it is us as outsiders that can see this, if you were sat on the photon as it passed a massive star and then on finally to a black hole event horizon the route would be totally arrow straight.

At some point prior to the event horizon things change and looking behind you at that point you'd see another you coming towards you, looking into the hole you'd see an infinite number of you... already there!

[AJI]

Is it posible to have a -ve mass ?
And therefore possibly have -ve gravity?
(I'm guessing it all hypothetical and part of the 'creative' maths you mention above)?

[mattnunn]

I have a very simple, most likely stupid, question that's always bugged me.

If the earth were to disappear or it's gravity to disappear and we were left to float in space would we be drawn into the sun by it's gravity or would we just hang there trapped in an orbit like earth does.

[Jinx]

mattnunn said:

I have a very simple, most likely stupid, question that's always bugged me.

If the earth were to disappear or it's gravity to disappear and we were left to float in space would we be drawn into the sun by it's gravity or would we just hang there trapped in an orbit like earth does.

Going back to Newton (F=MA) if the force keeping us in orbit is not reduced that much by the loss of the earths gravity well (in comparison with the gravitation pull of the sun) then A must increase substationally to maintain the equation (reference frame is us) . Therefore we will accelerate - so either off into outerspace at a tangent or rapidly falling into the sun. Trapped in the same orbit is not an option.

[mattnunn]

Jinx said:

mattnunn said:

I have a very simple, most likely stupid, question that's always bugged me.

If the earth were to disappear or it's gravity to disappear and we were left to float in space would we be drawn into the sun by it's gravity or would we just hang there trapped in an orbit like earth does.

Going back to Newton (F=MA) if the force keeping us in orbit is not reduced that much by the loss of the earths gravity well (in comparison with the gravitation pull of the sun) then A must increase substationally to maintain the equation (reference frame is us) . Therefore we will accelerate - so either off into outerspace at a tangent or rapidly falling into the sun. Trapped in the same orbit is not an option.

Cheers, makes sense, but why might we fly off at a tangent? I realise with some means of thrust we could over come the sun's gravity, would breast stroke work?

[Gene Vincent]

AJI said:

Is it posible to have a -ve mass ?
And therefore possibly have -ve gravity?
(I'm guessing it all hypothetical and part of the 'creative' maths you mention above)?

Yeah, I can play games with the maths and conjure up almost anything, that is why Theoreticians are more decisive than other scientists, we can perform conjuring tricks with numbers and you have to be very disciplined not to take yourself off into a madhouse.

This difference in mindset is often the cause of tension between us and others.

But...

If we look at your question you could say that 'vacuum energy' is a sort of -ve gravity... and a -ve mass... and what drives the expansion of the Cosmos is in fact the huge vacuum of the nothingness of the greater Universe... you could say that and it is hard to refute, but can be.

Years of good mathematicians time has been spent looking at this hypothesis and it has merits and may still hold a truth within but not anywhere near as clear cut as I've outlined.

[IainT]

mattnunn said:

Jinx said:

mattnunn said:

I have a very simple, most likely stupid, question that's always bugged me.

If the earth were to disappear or it's gravity to disappear and we were left to float in space would we be drawn into the sun by it's gravity or would we just hang there trapped in an orbit like earth does.

Going back to Newton (F=MA) if the force keeping us in orbit is not reduced that much by the loss of the earths gravity well (in comparison with the gravitation pull of the sun) then A must increase substationally to maintain the equation (reference frame is us) . Therefore we will accelerate - so either off into outerspace at a tangent or rapidly falling into the sun. Trapped in the same orbit is not an option.

Cheers, makes sense, but why might we fly off at a tangent? I realise with some means of thrust we could over come the sun's gravity, would breast stroke work?

I suspect it's because (from F=MA) the F from the sun is constant, our A stays the same and our M is much lower than the earth's although that makes me think we'd drift towards the sun rather than out tangentially. i.e. the left side of the equation outbalances the right side.

[Laplace]

Gene Vincent said:

Laplace said:

I thought a black hole by definition was a point of infinite density?

No, you are perhaps thinking of the Singularity and although the term singularity is often applied to a Black Hole, it is a misnomer.

Infinite density applies to the original Singularity (note capital letter) the point of the start of this Cosmos any other singularity doesn't get the capital letter to denote what we're talking about.

I was referring to the singularity at the center of a black hole, doesn't this have infinite density? Surely by it's nature of having 0 volume it has infintie density, otherwise I'm confused.

wikipedia said:

At the center of a black hole as described by general relativity lies a gravitational singularity, a region where the spacetime curvature becomes infinite.[53] For a non-rotating black hole, this region takes the shape of a single point and for a rotating black hole, it is smeared out to form a ring singularity lying in the plane of rotation.[54] In both cases, the singular region has zero volume. It can also be shown that the singular region contains all the mass of the black hole solution.[55] The singular region can thus be thought of as having infinite density.

[Gene Vincent]

Laplace said:

Gene Vincent said:

Laplace said:

I thought a black hole by definition was a point of infinite density?

No, you are perhaps thinking of the Singularity and although the term singularity is often applied to a Black Hole, it is a misnomer.

Infinite density applies to the original Singularity (note capital letter) the point of the start of this Cosmos any other singularity doesn't get the capital letter to denote what we're talking about.

I was referring to the singularity at the center of a black hole, doesn't this have infinite density? Surely by it's nature of having 0 volume it has infintie density, otherwise I'm confused.

wikipedia said:

At the center of a black hole as described by general relativity lies a gravitational singularity, a region where the spacetime curvature becomes infinite.[53] For a non-rotating black hole, this region takes the shape of a single point and for a rotating black hole, it is smeared out to form a ring singularity lying in the plane of rotation.[54] In both cases, the singular region has zero volume. It can also be shown that the singular region contains all the mass of the black hole solution.[55] The singular region can thus be thought of as having infinite density.

We have had this discussion before, you are not fully comprehending the meaning in the text.

The cause of this type of singularity is a star, it will be about the size of Paris in diameter, it is NOT a singular point, but a large massive object of huge density, it is NOT infinite.

The hypothesis is that at the very centre of this Paris diametered object there is a point of infinite density, however, this cannot happen all that happens (mathematically) is that every point in this Paris diametered is just the same as the rest, just very massive and dense, but not infinitely dense, it is a big number granted, but not even vaguely close to infinite.

Just to add... the bit about spacetime curvature being 'infinite' is in straight forward terms gibberish.

Edited by Gene Vincent on Wednesday 12th September 18:07

[Laplace]

So what stops the gravitational collapse of the star to a Paris sized object?

[mattnunn]

Laplace said:

So what stops the gravitational collapse of the star to a Paris sized object?

La periferique, of course.

[Gene Vincent]

Laplace said:

So what stops the gravitational collapse of the star to a Paris sized object?

I don't understand exactly what you're asking (syntax error?).

My guess is you're asking why doesn't it collapse further?

The reason is that all singularities differ from the Singularity in that they are inherently asymptotic in the nature of their maths... a sort of 'this far, but no further' final resolution.

If I've misunderstood your question then sorry, rephrase it for me.

[Laplace]

Gene Vincent said:

I don't understand exactly what you're asking (syntax error?).

My guess is you're asking why doesn't it collapse further?

The reason is that all singularities differ from the Singularity in that they are inherently asymptotic in the nature of their maths... a sort of 'this far, but no further' final resolution.

If I've misunderstood your question then sorry, rephrase it for me.

Yes that's what I was asking.

I have more questions but I'm dragging things off topic so I'll leave it be.

[IainT]

mattnunn said:

Laplace said:

So what stops the gravitational collapse of the star to a Paris sized object?

La periferique, of course.

Genius.

[R300will]

This dark energy stuff that's forcing galaxies apart and making the universe expand faster and faster. -ve gravity?

[moreflaps]

Gene Vincent said:

As promised we need to take a look at Gravity.


At this point you are a bit lost, I'll try to help you...

When you are looking at these words on your screen the photons from the screen travel to your eyes in straight lines .

Err, bit of a physics slip there eh GV?

Cheers

[Derek Smith]

It's angels holding onto your ankles.

[moreflaps]

Isn't a simpler explanation that gravity is the projection of a higher order dimension onto the dimensions of Minkowski space time resulting in it not being flat ...

Cheers

[MiseryStreak]

Oh no, he's back. GV - your theory about a thread degrading rapidly at 250 posts has been supplanted, 40 seems nearer the mark.

How does the inflaton field come into this?