physics question

[Signal 11]

The thing is, you can put a plant in the dark and it will still grow, some of the 'green' plants they've shown look seriously etiolated..

So you think the microgravity is making it harder for the plants to make use of the light?

A search came up with this but it's all biology to me.

 

[moon]

That study is about the bending of shoots emerging from the seed when grown in microgravity, it seems more morphological than photosynthetic but they could be related as it seems to result in etiolation..

And yes I think there is a relationship between photosynthesis and gravity.. but its just a weird idea based around protein structures and the way energy is gathered from tertiary folding. It's why I was interested in the relationship between gravity and what I am calling negative space in...errrr space.

 

[NoXion]

I ran across this (Kerr black holes images and videos) page on Kerr black holes, and since it mentions "negative space", I was reminded of this thread.

The page offers some relatively simple explanations (or at least I could follow them easily enough) on the basics of black holes, and also offers pictures and videos attempting to convey what it would it would be like to travel into a rotating, uncharged eternal black hole and through the ring-shaped singularity within.

I strongly encourage everyone to read the link (moon especially), but here's the bit that mentions negative space:

Beyond the singularity: negative space

The ring singularity acts a little like the magical door of fantasy worlds: by going through it we end up in a different place than if we go around it. If we go around it, nothing remarkable happens. But if we go through it (I mean through the disk bounded by the ring, of course: it is best to avoid the ring itself, where curvature is infinite, if we do not wish to be crushed to something unnatural), the r coordinate becomes negative, and starts measuring the opposite of the distance to the black hole (which, from that side, no longer looks like a black hole): this region of space-time is known as negative space.

This negative space region is infinite, and, if we go far away in it in any direction (for very negative values of r, that is, away from the black hole), then space becomes flat again: so there is, in effect, an infinite world tucked beyond the black hole's ring singularity. This can be thought of as the black hole's flip side, or evil twin brother; but it should be emphasized that there is nothing strange about negative space in itself (deep negative space is just a flat region of space, and, of course, from the point of view of negative space, it is positive space which is lies beyond the black hole's ring singularity). It is the negative side of the black hole (or negative black hole—not to be confused with the white hole which will be described later), and the region near it, which is strange, not the deep negative space.

One question I am not addressing is whether we reach the same negative space by crossing the ring singularity from north side or from the south side (or, in a somewhat similar line of thought, if we enter negative space from the north, go around the ring in negative space, then cross it again from the north, do we re-enter the same positive space as we left). Mathematically, the most natural answer to this question is yes, because for the Kerr manifold to be an algebraic variety in a certain sense demands it; but general relativity, and the Kerr solution, is agnostic about this, becaues it only makes prescriptions about the local geometric properties of space-time, not about its global topology. (In a certain sense, the question is meaningless, because the Kerr metric is a mathematical abstraction and is empty, and it is meaningless to ask whether two empty and identical regions of space-time are actually the same or not. Real life black holes might not have a negative space anyway.)

A first surprise is that, in the negative side, the black hole is repulsive: there are no orbits around it with negative r, and it takes a considerable amount of energy to enter deep negative space (essentially, the particle's rest mass energy divided by the black hole's fraction of maximality, so the particle must be relativistic). Another surprise is that that there are no horizons on the negative side: seen from the deep negative space, the black hole is a naked singularity. This is one reason why it is believed that there are no negative black holes in our universe (i.e., black holes for which we would be in the deep negative sapce). A third surprising characteristic of the negative side of the black hole is that it contains the Carter time machine: there is a region, rougly in the shape of a torus having the ring singularity as its inner equator, in which a material particle can travel at infinite speed along the ring, thus returning to initial position in space and time after a finite amount of proper time, or even go back in time. It takes a tremendous amount of energy and calibration to do this (I know it because I've tried to produce a geodesic that does so, and failed), but in principle it is possible. And, of course, this is one of the points where it should be emphasized that the interior region of the Kerr metric is a mathematical abstraction which probably does not describe real life black holes accurately (more about this later).

 

[squirrelp]

for clarification though:

"Kerr black holes are purely theoretical"
How Time Travel Works

 

[Signal 11]

 

[moon]

I guess its not possible to talk about negative space and black holes etc without discussing General Relativity and how space time (the fabric of space??) is aparently bent by a mass... yes?

File:BBH gravitational lensing of gw150914.webm - Wikimedia Commons

 

[Signal 11]

I guess its not possible to talk about negative space and black holes etc without discussing General Relativity and how space time (the fabric of space??) is aparently bent by a mass... yes?

Yes.

"Spacetime tells matter how to move; matter tells spacetime how to curve."

Wheeler's succinct summary of Einstein's theory of general relativity, in Geons, Black Holes, and Quantum Foam (2000), p. 235.
John Archibald Wheeler - Wikiquote

 

[moon]

But is it really curved? Or could it be compressed around the edges of the mass?

I don't think its curved at all..

 

[NoXion]

But is it really curved? Or could it be compressed around the edges of the mass?

I don't think its curved at all..

What do you mean by compressed?

It's called spacetime curvature because it bends the trajectory of objects.

 

[moon]

Compressed as in, assuming that space-time seeks to complete itself and a mass within it is a disruption in the fabric of space, could it be that the space time that the mass displaces is gathered around the mass in a sort of compressed/concentrated form?

 

[existentialist]

Compressed as in, assuming that space-time seeks to complete itself and a mass within it is a disruption in the fabric of space, could it be that the space time that the mass displaces is gathered around the mass in a sort of compressed/concentrated form?

Speaking as someone with insufficient maths or physics to really understand this stuff, I think it's almost impossible to really get in amongst the conceptual stuff around things like this. I think we just have to accept, rather than challenge the detail of, things like space-time curvature, unless we're prepared to go off and learn all the - very complex - calculus and other mathematics necessary to get a handle on it.

I got very interested in string theory and supersymmetry a few years ago, and - much as I still find it fascinating to think about - I've had to accept that there's no way I'm really going to understand it beyond being able to mouth a few buzzwords (flop-transitions in Calabi-Yau manifolds, anyone? ).

I have to assume that, if something seems "wrong" or un-understandable, it's because of a deficiency of my understanding, not a problem inherent in the theory.

 

[moon]

Thats not how I am...
I like to question things so that my understanding is deepened.
I'm sorry that you feel this way but I am enjoying this thread and will continue to question things...

 

[existentialist]

?

 

[gosub]

What do you mean by compressed?

It's called spacetime curvature because it bends the trajectory of objects.

As does a glass of water bend a stick....differing density

 

[existentialist]

Thats not how I am...
I like to question things so that my understanding is deepened.
I'm sorry that you feel this way but I am enjoying this thread and will continue to question things...

I'm not suggesting you don't question things. But be aware that, particularly at the kind of level of knowledge that people like you and I are at in regard to things like relativity, cosmology, and quantum mechanics, the Dunning Kruger effect is prone to coming into play.

 

[NoXion]

As does a glass of water bend a stick....differing density

the stick doesn't bend, the light rays coming off it do.

 

[gosub]

the stick doesn't bend, the light rays coming off it do.

which are the things with trajectory

 

[NoXion]

which are the things with trajectory

the trajectory of an object moving through a curved space-time is different though. It's relatively gentle bends, compared to the sharp turns made by photons as they encounter materials with different refractive indices.

 

[existentialist]

the trajectory of an object moving through a curved space-time is different though. It's relatively gentle bends, compared to the sharp turns made by photons as they encounter materials with different refractive indices.

And, from the perspective of the space time in question, they're not even bends

 

[moon]

I'm not suggesting you don't question things. But be aware that, particularly at the kind of level of knowledge that people like you and I are at in regard to things like relativity, cosmology, and quantum mechanics, the Dunning Kruger effect is prone to coming into play.

You don't know anything about me...

 

[existentialist]

You don't know anything about me...

I know a little about you. For example, I suspect that our knowledge of the mathematics underlying general relativity is comparable.

 

[moon]

So what are you saying, that I should shut the fuck up?

 

[Signal 11]

I don't think its curved at all..

What observations do you think are not adequately explained by GR, and how does your alternative idea explain them?

 

[existentialist]

So what are you saying, that I should shut the fuck up?

If you read what I am saying, it should be very clear that at no point am I saying such a thing. It was meant to be a helpful word-to-the-wise. I'm sorry that you haven't taken it in that spirit, and will shut up now.

 

[moon]

What observations do you think are not adequately explained by GR, and how does your alternative idea explain them?

I'll reply when I've calmed down a bit..

 

[2hats]

Speaking as someone with insufficient maths or physics to really understand this stuff, I think it's almost impossible to really get in amongst the conceptual stuff around things like this. I think we just have to accept, rather than challenge the detail of, things like space-time curvature, unless we're prepared to go off and learn all the - very complex - calculus and other mathematics necessary to get a handle on it.

Bringing you neatly back to the cartoon in post 58.

 

[existentialist]

Bringing you neatly back to the cartoon in post 58.

 

[moon]

What observations do you think are not adequately explained by GR, and how does your alternative idea explain them?

I was wondering if space/time was concentrated around a mass like in the picture below, where the central bit would be the mass and the darker areas around it is sort of like compressed space fabric.

 

[NoXion]

Compressed as in, assuming that space-time seeks to complete itself and a mass within it is a disruption in the fabric of space, could it be that the space time that the mass displaces is gathered around the mass in a sort of compressed/concentrated form?

Why would space-time "seek to complete itself"? Anything outside of space and time is by definition not within the universe, and therefore has no causal relationship with anything we can observe. Space-time has no need (none that has been shown, anyway) to "complete" itself because it is already omnipresent. Why make that assumption?

How is a mass a "disruption" in space-time? How is this different to mass bending space-time?

How does mass "displace" space-time? Because it sounds like you're saying that there's literally nothing (not even empty space, which is implied by "displaced") within say, the Earth, which is patently untrue.

I was wondering if space/time was concentrated around a mass like in the picture below, where the central bit would be the mass and the darker areas around it is sort of like compressed space fabric.
View attachment 126082

Why would it be? Your suggestion begs the question because it hasn't been established that space-time is "displaced/disrupted/compressed" rather than "curved" by mass.

 

[Combustible]

The problem with the rubber sheet analogy for general relativity is not that it's an oversimplification, it's just wrong, it is circular (what makes the balls fall into the dips in the sheet?), and it just doesn't explain anything about how the theory works.

A better explanation for showing how curved space time can lead to effects of gravity is in this video. The 'bending' of the time part of space-time is another thing missed by the rubber sheet analogy, when this actually explains nearly all of the everyday effects of gravity.