A friend asked today "how can dark energy appear to act as anti-gravity to expand space and what might it be"?
I had this inspiration:
How do we reconcile dark energy's anti-gravity like behaviour of actually accelerating the inflation of our entire Universe? Well the answer is simple and profound - real estate, or position is everything!
Here are two critical assumptions based on observations:
1) 80% of the Universe appears to be made up from dark energy - so there is alot of it!
2) Accept for a moment that Dark Energy asserts a normal gravitational effect on normal matter and energy but not itself (there is justification for this but its cryptic and I'll leave it out for a moment).
Adding those two factors leads you to realsie two important things:
1) Position is king! By this I mean the galactic layout / shape / position / distribution of all this energy - i.e. where it sits geographically in the cosmos is critical
2) Unlike normal matter / energy it won't clump because of gravity into suns, planets, people, trees and rocks etc. - it will most likely spread out diffusely very, very, very evenly - unbelieveably so (why I'll theorise a bit later).
So put this all together....
Visualise our own solar system. Most of the visible Mass is centred in the Sun, then Planets, then asteroids, then dust, until you get to the vaccuum of space where there is generally 1 - 3 hydrogen atoms per cubic metre. But the dark mass is spread evenly and might account for significant equivalent gravitational mass. Put this aside and next step out side our solar system and proceed to our galaxy, the Milky Way. There is alot of empty space in the Milky Way - potentially chock full of dark energy exerting a gravitational pull.
Now step outside our galaxy and even the galactic cluster containing the Milky Way as one of its many galaxies. Between it and the next galactic cluster is a truly vast amount of empty space - again possible full of dark energy - hence alot of gravity. Possibly enough to explain the observed rotational speeds vs mass of distant galaxies that led us to dark matter / dark energy and Modified Newtonian Dynamics (MOND).
As the Universe expands allow the dark energy to expand roughly in proportion with it - allowing it to be evenly distrubuted but still bounded by any edge to our Universe. Well this means dark energy is spread evenly throughout, but normal matter / energy tends to be clustered more towards the centre or in galactic cluster to be more accurate. Imagine a shape to the Universe - say a rough sphere. The gravitational effect of dark energy - by location and volume - there is more at the volume as you move out from the centre of a sphere. So gravity from dark energy tends to pulls things out towards the 'edge of the Universe' whilst normal energy / matter tries to pull things all back together back towards a big crunch scenario. Remember from my other thread (a while ago) - gravity is the one elemntal force that isn't quantised - so its effects can apparently go on towards infinity - rather than dwindle to nothing once your distance from a gravitational source is so vast your gravitational force is below the lowest quanta of energy a photon can have.
* * * * Correction to improve the maths
Something told me I'd missed something here, and I realised what it was working on a simple sphere, and asking why would dark energy exert a gravitational force causing expansion rather than contraction sheerly because of its consisten distribution. After all any point away from the centre has more mass between it and the opposite size of the sphere (pulling it back to the centre) than between it and the closest edge to the sphere.
But then I realised 1) the Universe is expanding (unfolding) in all directions at say the speed of light. So opposite edges are receding at apparently (realivisticly) slightly more than twice the speed of light (i.e. the Universe is 14.8 billion years old but believed to have a diameter of 40 billion light years). So many points away from the centre are simply too far away from the opposite edge to every experience its gravitational influence (spacetime warps / gravity must propogate at the speed of light).
So when measuring gravity at any abstract point in a large Universe - as you go thousands or millions of light years out from this point you are actually experiencing the gravitation forces of how the Universe was millions or even billions of years ago. The mass or energy whose gravity you experience could have long since moved or dissipated, possibly millions or even billions of years ago. So combined this means the closer edge of the Universe will have more impact on you, and as it is receding from you it will sort of pull you along. The opposite edge from you is too far away and receding faster than c relative to you so its gravitational influence will never catch up to you. In a Universe expanding at c in all directions, far away from its centre you are moving away so fast from the mass on the other side of the Universe its gravitational pull (wave) can never catch up to you to pull you back!!!
I'd love to model that on a super computer.
* * * *
Finally my own thoughts on what dark energy may be and why it alone is evenly distributed:
M-Theory and superstring symmetry theory postulates we live in a 10 or 11 dimensional rality called a membrane. We commonly observe only 4 of these dimensions space (3) plus mass (=energy) (1). In our reality with our human perception time is wrapped into spacetime, although it might be something very different within our reality and across other membranes, but I digress.
The other 6 or 7 hidden dimensions may be so tiny (think Planck level small 10 ^ -35 metre) and subtle its hard to every observe them. But on a galactic or universal scale these dimensions could significantly affect our percieved reality. Possible what we call dark energy is small periodic leakages of regular energy and mass into and out of these hidden dimensions everywhere (what theorists call quantum foam of spacetime). So I postulate spacetime isn't static - it may be an equilibrium point of normal energy and matter leaking into and back from hidden dimensions in M-Theory. This leakage maybe appearing to us as dark energy and dark matter. Dark matter might just be s-particles or symmetric particles (s-electron, s-neutron, s-proton etc) from string theory. CERN will test this theory in 2007.
So that is a theory on what is Dark Energy (and how it appears). Why is it evenly distributed in spacetime when nothing else is? Because it's the very fabric of our reality itself - it itself is our dimensional infrastructure, so it has to be everywhere by its very definition. This also adds weight (pun intended) on why dark energy doesn't directly effect itself. Those hidden dimension have their own rules for how they interact - what we postulate as dark energy and dark matter might just be leakage from our realities hidden dimensions!
As I said this is my intuition - arrived at this morning - and if I am right I want the Noble prize please!!! Call it the Kendall conjecture
I had this inspiration:
How do we reconcile dark energy's anti-gravity like behaviour of actually accelerating the inflation of our entire Universe? Well the answer is simple and profound - real estate, or position is everything!
Here are two critical assumptions based on observations:
1) 80% of the Universe appears to be made up from dark energy - so there is alot of it!
2) Accept for a moment that Dark Energy asserts a normal gravitational effect on normal matter and energy but not itself (there is justification for this but its cryptic and I'll leave it out for a moment).
Adding those two factors leads you to realsie two important things:
1) Position is king! By this I mean the galactic layout / shape / position / distribution of all this energy - i.e. where it sits geographically in the cosmos is critical
2) Unlike normal matter / energy it won't clump because of gravity into suns, planets, people, trees and rocks etc. - it will most likely spread out diffusely very, very, very evenly - unbelieveably so (why I'll theorise a bit later).
So put this all together....
Visualise our own solar system. Most of the visible Mass is centred in the Sun, then Planets, then asteroids, then dust, until you get to the vaccuum of space where there is generally 1 - 3 hydrogen atoms per cubic metre. But the dark mass is spread evenly and might account for significant equivalent gravitational mass. Put this aside and next step out side our solar system and proceed to our galaxy, the Milky Way. There is alot of empty space in the Milky Way - potentially chock full of dark energy exerting a gravitational pull.
Now step outside our galaxy and even the galactic cluster containing the Milky Way as one of its many galaxies. Between it and the next galactic cluster is a truly vast amount of empty space - again possible full of dark energy - hence alot of gravity. Possibly enough to explain the observed rotational speeds vs mass of distant galaxies that led us to dark matter / dark energy and Modified Newtonian Dynamics (MOND).
As the Universe expands allow the dark energy to expand roughly in proportion with it - allowing it to be evenly distrubuted but still bounded by any edge to our Universe. Well this means dark energy is spread evenly throughout, but normal matter / energy tends to be clustered more towards the centre or in galactic cluster to be more accurate. Imagine a shape to the Universe - say a rough sphere. The gravitational effect of dark energy - by location and volume - there is more at the volume as you move out from the centre of a sphere. So gravity from dark energy tends to pulls things out towards the 'edge of the Universe' whilst normal energy / matter tries to pull things all back together back towards a big crunch scenario. Remember from my other thread (a while ago) - gravity is the one elemntal force that isn't quantised - so its effects can apparently go on towards infinity - rather than dwindle to nothing once your distance from a gravitational source is so vast your gravitational force is below the lowest quanta of energy a photon can have.
* * * * Correction to improve the maths
Something told me I'd missed something here, and I realised what it was working on a simple sphere, and asking why would dark energy exert a gravitational force causing expansion rather than contraction sheerly because of its consisten distribution. After all any point away from the centre has more mass between it and the opposite size of the sphere (pulling it back to the centre) than between it and the closest edge to the sphere.
But then I realised 1) the Universe is expanding (unfolding) in all directions at say the speed of light. So opposite edges are receding at apparently (realivisticly) slightly more than twice the speed of light (i.e. the Universe is 14.8 billion years old but believed to have a diameter of 40 billion light years). So many points away from the centre are simply too far away from the opposite edge to every experience its gravitational influence (spacetime warps / gravity must propogate at the speed of light).
So when measuring gravity at any abstract point in a large Universe - as you go thousands or millions of light years out from this point you are actually experiencing the gravitation forces of how the Universe was millions or even billions of years ago. The mass or energy whose gravity you experience could have long since moved or dissipated, possibly millions or even billions of years ago. So combined this means the closer edge of the Universe will have more impact on you, and as it is receding from you it will sort of pull you along. The opposite edge from you is too far away and receding faster than c relative to you so its gravitational influence will never catch up to you. In a Universe expanding at c in all directions, far away from its centre you are moving away so fast from the mass on the other side of the Universe its gravitational pull (wave) can never catch up to you to pull you back!!!
I'd love to model that on a super computer.
* * * *
Finally my own thoughts on what dark energy may be and why it alone is evenly distributed:
M-Theory and superstring symmetry theory postulates we live in a 10 or 11 dimensional rality called a membrane. We commonly observe only 4 of these dimensions space (3) plus mass (=energy) (1). In our reality with our human perception time is wrapped into spacetime, although it might be something very different within our reality and across other membranes, but I digress.
The other 6 or 7 hidden dimensions may be so tiny (think Planck level small 10 ^ -35 metre) and subtle its hard to every observe them. But on a galactic or universal scale these dimensions could significantly affect our percieved reality. Possible what we call dark energy is small periodic leakages of regular energy and mass into and out of these hidden dimensions everywhere (what theorists call quantum foam of spacetime). So I postulate spacetime isn't static - it may be an equilibrium point of normal energy and matter leaking into and back from hidden dimensions in M-Theory. This leakage maybe appearing to us as dark energy and dark matter. Dark matter might just be s-particles or symmetric particles (s-electron, s-neutron, s-proton etc) from string theory. CERN will test this theory in 2007.
So that is a theory on what is Dark Energy (and how it appears). Why is it evenly distributed in spacetime when nothing else is? Because it's the very fabric of our reality itself - it itself is our dimensional infrastructure, so it has to be everywhere by its very definition. This also adds weight (pun intended) on why dark energy doesn't directly effect itself. Those hidden dimension have their own rules for how they interact - what we postulate as dark energy and dark matter might just be leakage from our realities hidden dimensions!
As I said this is my intuition - arrived at this morning - and if I am right I want the Noble prize please!!! Call it the Kendall conjecture
