Although nobody has a good idea of what dark energy is, has anyone been able to constrain its effects to a minimum distance - like a million light years, for instance?
Chris
Chris
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ramparts":3ked8tsr said:
Really? I think looking at dark energy as anit-gravity is misleading. I have a couple of concerns with this characterisations, besides the obvious that as the objects got farther away the anti-gravity effect would decrease, unless anti-gravity gets stronger with distance.
The main concern is that means that mass are moving away from each other in the in the universe. This implies (at least to me) a large container with things moving away from each other in the constant sized container. The other problem is if it is anti-gravity that moving the objects away from each other then the objects can atain super luminal speeds as opposed to the objecst simply moving with the expanding space at super luminal speeds.
csmyth3025":20vb00yj said:
There really is no minimum distance. The local affects of even the expansion are usually overcome by gravity. Even though the universe is expanding the andromeda galaxy is getting closer to us. We are gravitationally connected and will eventually collide.
The expansion rate that I found on the NASA site: Between 50 (km/sec)/Mpc and 100 (km/sec)/Mpc. Where Mpc is megaparsecs. That is not very much, but it really adds up over a few billion light years!
I have not found any hard numbers for the acceleration of the expansion. Again there is no minimum distance per se that that the acceleration is affecting, but to be able to detect the acceleration it may take measurements on the order of billions of light years.
origin":2memn8ow said:
If if helps, I found the following information in Wikipedia's article on the Hubble Constant:
"...The law is often expressed by the equation v = H0D, with H0 the constant of proportionality (the Hubble constant) between the distance D to a galaxy and its velocity v. The SI unit of H0 is s-1 but it is most frequently quoted in (km/s)/Mpc, thus giving the speed in km/s of a galaxy one Megaparsec away. The reciprocal of H0 is the Hubble time.
The most recent observational determination of the proportionality constant obtained in 2009 by using the Hubble Space Telescope (HST) yielded a value of H0 = 74.2 ± 3.6 (km/s)/Mpc.[4] The results agree closely with an earlier measurement of H0 = 72 ± 8 km/s/Mpc obtained in 2001 also by the HST.[5] In August 2006, a less-precise figure was obtained independently using data from NASA's Chandra X-ray Observatory: H0 = 77 (km/s)/Mpc or about 2.5×10−18 s−1 with an uncertainty of ± 15%.[6] NASA summarizes existing data to indicate a constant of 70.8 ± 1.6 (km/s)/Mpc if space is assumed to be flat, or 70.8 ± 4.0 (km/s)/Mpc otherwise.[7]..."
Also, I found a 59 page research paper on cosmic acceleration here:
http://supernova.lbl.gov/public/papers/ ... mology.pdf
entitled: "Measurement of m, from a blind analysis of Type Ia
supernovae with CMAGIC: Using color information to verify the
acceleration of the Universe"
I don't pretend to understand any of it, but it seems to me that the paper puts some constraints on the acceleration of cosmic expansion on page 21 under the heading "Cosmological Results". If anyone would be so kind as to take a look at this and let me know what, in general, this paper is saying it would be very helpful. Since I don't understand it, it may be that the paper actually has nothing to do with the rate of acceleration of the cosmic expansion.
Chris
origin":37y6tefd said:
Why would some anti-gravitational effect suddenly mean recession speeds were due to to motion through space?
If gravity can slow the rate of expansion, as it had done for 8 billion years or so, why couldn't something that acts like repulsive gravity across large scales accelerate the rate of expansion?
For most of the last century, when we thought the rate was still decelerating due to gravity, we used the same FLRW solution to Einstein's field equations to describe the expansion of the universe as we do now, the only recent difference is an added parameter or two for dark energy and matter. The FLRW solution uses ideas based on an ideal fluid or gas to represent space as a kind of "cosmic fluid" that can expand or contract and drags everything in the universe along with it. How it expands or contracts depends mostly on two things.. the initial conditions or "impetus" that led to expansion, and how the gravity (amongst other things) of the contents of the universe as a whole deals with that initial impetus.
The FLRW solution is only really a first order approximation - it only really describes things at the largest scales as it makes the assumption of a perfectly homogeneous universe, which ours is not - it is quite lumpy! It is the gravity of everything in the universe that slows down the rate of expansion of the cosmic fluid, so rather than thinking of one thing repulsing or tugging on another which repulses or tugs on another etc etc ad finitum and then wondering whether it moves through the fluid or not, perhaps it is worth considering the overall gravity of the universe would act as a pressure on the gas, but in a negative way. Negative pressure, pulling all the gas together, fighting with the tendency for the gas to expand?
Anyway, if gravity can slow down the rate at which "space" expands, why couldn't some form of "anti" gravity speed up the rate at which "space" expands?
SpeedFreek":dqebbjyf said:Why would some anti-gravitational effect suddenly mean recession speeds were due to to motion through space?
If gravity can slow the rate of expansion, as it had done for 8 billion years or so, why couldn't something that acts like repulsive gravity across large scales accelerate the rate of expansion?
For most of the last century, when we thought the rate was still decelerating due to gravity, we used the same FLRW solution to Einstein's field equations to describe the expansion of the universe as we do now, the only recent difference is an added parameter or two for dark energy and matter. The FLRW solution uses ideas based on an ideal fluid or gas to represent space as a kind of "cosmic fluid" that can expand or contract and drags everything in the universe along with it. How it expands or contracts depends mostly on two things.. the initial conditions or "impetus" that led to expansion, and how the gravity (amongst other things) of the contents of the universe as a whole deals with that initial impetus.
The FLRW solution is only really a first order approximation - it only really describes things at the largest scales as it makes the assumption of a perfectly homogeneous universe, which ours is not - it is quite lumpy! It is the gravity of everything in the universe that slows down the rate of expansion of the cosmic fluid, so rather than thinking of one thing repulsing or tugging on another which repulses or tugs on another etc etc ad finitum and then wondering whether it moves through the fluid or not, perhaps it is worth considering the overall gravity of the universe would act as a pressure on the gas, but in a negative way. Negative pressure, pulling all the gas together, fighting with the tendency for the gas to expand?
Anyway, if gravity can slow down the rate at which "space" expands, why couldn't some form of "anti" gravity speed up the rate at which "space" expands?
Good points speedfreek and like I said before ramparts certainly understands much more than I do. Actually, after I posted that reply, I begain to think about gravity slowing the expansion of the universe. And after reading your response I thought about the local effect of gravity on expansion relative to the larger overall effect of gravity on expansion. I have managed to become rather confused on the nature of the expansion - which is a good thing because that is going to lead me to do some research.
origin":l3nnv5eq said:SpeedFreek":l3nnv5eq said:Why would some anti-gravitational effect suddenly mean recession speeds were due to to motion through space?
If gravity can slow the rate of expansion, as it had done for 8 billion years or so, why couldn't something that acts like repulsive gravity across large scales accelerate the rate of expansion?
For most of the last century, when we thought the rate was still decelerating due to gravity, we used the same FLRW solution to Einstein's field equations to describe the expansion of the universe as we do now, the only recent difference is an added parameter or two for dark energy and matter. The FLRW solution uses ideas based on an ideal fluid or gas to represent space as a kind of "cosmic fluid" that can expand or contract and drags everything in the universe along with it. How it expands or contracts depends mostly on two things.. the initial conditions or "impetus" that led to expansion, and how the gravity (amongst other things) of the contents of the universe as a whole deals with that initial impetus.
The FLRW solution is only really a first order approximation - it only really describes things at the largest scales as it makes the assumption of a perfectly homogeneous universe, which ours is not - it is quite lumpy! It is the gravity of everything in the universe that slows down the rate of expansion of the cosmic fluid, so rather than thinking of one thing repulsing or tugging on another which repulses or tugs on another etc etc ad finitum and then wondering whether it moves through the fluid or not, perhaps it is worth considering the overall gravity of the universe would act as a pressure on the gas, but in a negative way. Negative pressure, pulling all the gas together, fighting with the tendency for the gas to expand?
Anyway, if gravity can slow down the rate at which "space" expands, why couldn't some form of "anti" gravity speed up the rate at which "space" expands?
Good points speedfreek and like I said before ramparts certainly understands much more than I do. Actually, after I posted that reply, I begain to think about gravity slowing the expansion of the universe. And after reading your response I thought about the local effect of gravity on expansion relative to the larger overall effect of gravity on expansion. I have managed to become rather confused on the nature of the expansion - which is a good thing because that is going to lead me to do some research.
You and me both brother. I k now I am not a scientist, but after all this reading I am beginning to think that gravity is working on all of the solar systems, planets, suns. Anything physical, but not interstellar space. I will study more and get back.
csmyth3025":1lxwk358 said:
This is a paper that I'd say is mostly of interest to observational astronomers
It's using a new method to estimate the acceleration from supernovae data that they claim has some advantages over other methods of using supernovae, making cosmic dust less of an issue and so on. It's really just a consistency check with the familiar results from those other methods. The results don't really tell us much more about the universe, they just show that this method might in principle be able to do that in the future. I haven't heard about this before, though, as I'm not in the supernovae field Thanks for the overview, Ramparts. Do you know if there is a firm estimate of the rate at which the expansion of the universe is accelerating?
Chris
Chris
The error bars on those measurements are pretty large. About all we can say now is that the evidence indicates that the rate of expansion is increasing...giving a precise number is impossible.
However, the dark energy proportion of the Universe's mass-energy is supported by multiple lines of evidence, and does not depend on a precise measure of that rate.
However, the dark energy proportion of the Universe's mass-energy is supported by multiple lines of evidence, and does not depend on a precise measure of that rate.
I can remember when the scientific debate was about whether there was enough mass/energy in the universe for it to be closed (ending in a big crunch) or if there was insufficient mass to slow the initial expansion, making the universe open (expanding forever, but at a gradually slower rate). I would like to have seen the look on the researcher's faces when they were trying to measure how much the expansion was slowing down and, instead, found it was speeding up. I'll bet their reaction was something like "Oh, crap! What did we do wrong?"
Chris
Chris
That's absolutely correct. I've read anecdotes from those who first found the result. They held up publication of their results for quite a while while they checked, rechecked and checked their results again, since they thought they had done something wrong in analyzing the data. Finally, they had no other path than to release the results that shook things up so much.
As I said, since then the "dark energy" content of the Universe has been measured in many other independent ways, but it's something to take that first step.
As I said, since then the "dark energy" content of the Universe has been measured in many other independent ways, but it's something to take that first step.
Would not all the objects in the "container" then be collected along the inside boundary? forced to the "under surface" or "inside surface" of the container? With dark energy repelling it to its farthest point........
And if the container were round (like a transparent balloon), would the Universe then be projected onto the surface of said container? As more and more "stuff" gets pushed to the outer edge, more and more edge would be needed to hold the "stuff" Perhaps Dark energy is indeed fueling expansion. Or would it bounce of only to be redirected back to the edge?
I wonder. Could dark energy along with dark matter be the very "stuff" that keeps the Universe from falling apart? Somehow interacting with everything "just right" to hold everything to the surface of the Universe? To the surface of that "balloon"?
Just some thoughts
Star
Edit: I keep confusing Dark Matter with Dark Energy. I have edited the original post to reflect energy and not matter as it was originally
Fallingstar1971":2liy17e4 said:
One interesting take on the ballon analogy is the possibility that the universe is a spatially 3-dimensional "surface" of a "balloon" that's expanding in a fourth spatial dimension that we can't perceive. Unfortunately, until such time as we are able to detect such a fourth dimension, this idea will remain pure speculation.
Still, I wonder if any cosmologists have investigated the properties of a theoretical model of this type.
Chris
Chris - most certainly But it is much more subtle than that. This is actually one of the biggest problems with the balloon analogy, which is otherwise a fantastic way to demonstrate some very complicated mathematics. General relativity and cosmology are set within a mathematical framework called Riemannian geometry. As you probably know, this is different from our standard Euclidean geometry, which is what we're used to and think in. In Euclidean geometry, a curved surface where Euclid's laws don't hold needs to be embedded in a higher-dimensional flat space where the Euclidean laws do stay true. But in Riemannian geometry, a generalization of Euclidean geometry, this need not be true. There's nothing special about Euclidean spaces (or flat spaces), so spaces can have what is called intrinsic curvature, and this need not be flat. An example of this is a two-dimensional universe shaped like the surface of a sphere (like the Earth or a balloon), and the fascinating thing is that there is no need for it to be embedded in a three-dimensional space which is flat. This curved two-dimensional space can just exist on its own.
The universe, to the best of our knowledge, works like this. It can have any various curvature, including a spherical-type curvature like the balloon surface, where you go out one end and come back on the other, but that need not a fifth dimension to happen. Scientists have examined the possibility of there being a fifth-dimension, and these theories are testable (eventually), but for entirely different reasons.
But it is much more subtle than that. This is actually one of the biggest problems with the balloon analogy, which is otherwise a fantastic way to demonstrate some very complicated mathematics. General relativity and cosmology are set within a mathematical framework called Riemannian geometry. As you probably know, this is different from our standard Euclidean geometry, which is what we're used to and think in. In Euclidean geometry, a curved surface where Euclid's laws don't hold needs to be embedded in a higher-dimensional flat space where the Euclidean laws do stay true. But in Riemannian geometry, a generalization of Euclidean geometry, this need not be true. There's nothing special about Euclidean spaces (or flat spaces), so spaces can have what is called intrinsic curvature, and this need not be flat. An example of this is a two-dimensional universe shaped like the surface of a sphere (like the Earth or a balloon), and the fascinating thing is that there is no need for it to be embedded in a three-dimensional space which is flat. This curved two-dimensional space can just exist on its own.The universe, to the best of our knowledge, works like this. It can have any various curvature, including a spherical-type curvature like the balloon surface, where you go out one end and come back on the other, but that need not a fifth dimension to happen. Scientists have examined the possibility of there being a fifth-dimension, and these theories are testable (eventually), but for entirely different reasons.
So another way to view it is as a blanket wadded up into an untidy ball (the blanket is flat, but the space it resides in is not)?
Unfortunately, since the world we live in is very nearly Euclidean and thus our intuition is entirely Euclidean, there's really no analogy that entirely gets at intrinsic curvature. The blanket in your example is still embedded in a higher (three-dimensional) Euclidean space. The best we can do is use examples like the balloon or that blanket and just add at the end "oh, and they can exist on their own without a higher dimensional space to be 'in.'" It's the concept of every space which isn't flat needing to be 'in' a higher-dimensional flat space which is in our experience but is not necessary in the universe as a whole.
The Universe is not expanding, it is actually contracting. If you take all of the blackholes that reside in the strings of our Mega Galaxy that has yet to be named, these blackholes would be pulling matter to their singularities which would not allow the Universe to expand. Then we have the Mega Blackhole at the center of our Mega Galaxy that is pulling all matter towards it. All of these factors would point to our Mega Galaxy being pulled towards these smaller blackholes first and then the larger one at the center of our black instead of expanding outwards.
So much ignorance of physics in one little post.
The Universe is expanding. It has been measured as doing so for half a century. Take your head out of the sand.
We do not have a "Mega" black hole at the center of our galaxy. It is a supermassive black hole. It is pulling matter toward it with the force of gravity, but the stars in the galaxy are not being sucked in. They continue on their merry way in orbit just as they have for more than 10 billion years.
The Universe is expanding. It has been measured as doing so for half a century. Take your head out of the sand.
We do not have a "Mega" black hole at the center of our galaxy. It is a supermassive black hole. It is pulling matter toward it with the force of gravity, but the stars in the galaxy are not being sucked in. They continue on their merry way in orbit just as they have for more than 10 billion years.
MeteorWayne, that's actually completely wrong. We've known that the universe is expanding for over 3/4 of a century
Hello,
I am a new member of space.com I don't know how to add a post but I like to give you some important information which is some what related to "BIG BANG THEORY" but is related to black holes.
First: Actually what you think black hole is? I will to mention you the true answer: "There is nothing like black holes generally what every body knows a dead star. The star after burning most of the fuel from its outer surface and after the supernova the surface of the star cooled down and it becomes a planet which liberate energy but that energy is so less that it is not visible from light years distance compare it as a planet like Venus or mercury say.
Now I will like to mention one new thing that also our planet Earth is also a star but it is not having so much high surface temperature because due to the presence of surrounded water.
Second: we think that our planet is been protected by the large gravitational force of planet Jupiter from numerous asteroids: It may be true from our common thinking. Tell me brother what happen if a big asteroid strike a surface or let say you bombard a hard stone or metal to a surface with a high velocity and momentum that portion of surface will heat up. Same thing is happening there and also to planets like sun, Venus, Mercury, Jupiter, Natural satellites etc.
There will be time when all those planet will become so hot that they will become a star like object and start heating our planet and after may be 200-300 years later our planet will also become a star as all the water will be vaporized and all the life will extinct from our planet.
For example let say the nuclear weapons ,fuels ,reactors which we are getting from our own earth and also I like to mention that all the 9 planets were born from our main star sun that means all planets have that source to develop the energy more the planet will heat up more there chances of converting into stars.
Next thing the water which exists in our planet are protecting our planet convert into star & due to green house effect they are vaporizing and thus our planet is heating up thus we must have to cut the green house emigration, fossil fuel burning, destruction of forest, nuclear warheads testing and also the war upto to 0%. Still there is danger.
Every planet when they are converting into star after thousands of year later will become cool not like the 9th planet but surface temperature will be some what cool. Like this "cycles will be repeated" explained below.
Third: Another thing I like to say that there will be no planetary collision like "nebula" or some think like that not may be now, but when after thousands or billion of years I can't say the exact date after, when all the solar system will collide together i.e. all the universe, stars, planets that will again will make a "Primeval Atom" and again new "Big bang will start" for that I think there is long time.
But what I had mentioned above is due to my long time study & imagination in science and technology field.
Thank you.
I am a new member of space.com I don't know how to add a post but I like to give you some important information which is some what related to "BIG BANG THEORY" but is related to black holes.
First: Actually what you think black hole is? I will to mention you the true answer: "There is nothing like black holes generally what every body knows a dead star. The star after burning most of the fuel from its outer surface and after the supernova the surface of the star cooled down and it becomes a planet which liberate energy but that energy is so less that it is not visible from light years distance compare it as a planet like Venus or mercury say.
Now I will like to mention one new thing that also our planet Earth is also a star but it is not having so much high surface temperature because due to the presence of surrounded water.
Second: we think that our planet is been protected by the large gravitational force of planet Jupiter from numerous asteroids: It may be true from our common thinking. Tell me brother what happen if a big asteroid strike a surface or let say you bombard a hard stone or metal to a surface with a high velocity and momentum that portion of surface will heat up. Same thing is happening there and also to planets like sun, Venus, Mercury, Jupiter, Natural satellites etc.
There will be time when all those planet will become so hot that they will become a star like object and start heating our planet and after may be 200-300 years later our planet will also become a star as all the water will be vaporized and all the life will extinct from our planet.
For example let say the nuclear weapons ,fuels ,reactors which we are getting from our own earth and also I like to mention that all the 9 planets were born from our main star sun that means all planets have that source to develop the energy more the planet will heat up more there chances of converting into stars.
Next thing the water which exists in our planet are protecting our planet convert into star & due to green house effect they are vaporizing and thus our planet is heating up thus we must have to cut the green house emigration, fossil fuel burning, destruction of forest, nuclear warheads testing and also the war upto to 0%. Still there is danger.
Every planet when they are converting into star after thousands of year later will become cool not like the 9th planet but surface temperature will be some what cool. Like this "cycles will be repeated" explained below.
Third: Another thing I like to say that there will be no planetary collision like "nebula" or some think like that not may be now, but when after thousands or billion of years I can't say the exact date after, when all the solar system will collide together i.e. all the universe, stars, planets that will again will make a "Primeval Atom" and again new "Big bang will start" for that I think there is long time.
But what I had mentioned above is due to my long time study & imagination in science and technology field.
Thank you.
Generally, I like to be civil in responding to posts. This one by sam185 is so off-the-wall that I really do wonder what he's smoking.
Chris
Chris
ramparts":1jnu60hf said:
I think I have a glimpse of what your talking about - which I believe is the concept of "manifolds" and their properties. I have only a very vague idea how mathematicians and cosmologists actually use manifolds except to say that they are very heavily mathematical. Wikipedia has a very good article on manifolds - most of it is too advanced for me, though.
The following paragraph from the Wikipedia article sort of encapsulates both the usefulness and complexity of manifolds:
"...The concept of manifolds is central to many parts of geometry and modern mathematical physics because it allows more complicated structures to be expressed and understood in terms of the relatively well-understood properties of simpler spaces. For example, a manifold is typically endowed with a differentiable structure that allows one to do calculus and a Riemannian metric that allows one to measure distances and angles. Symplectic manifolds serve as the phase spaces in the Hamiltonian formalism of classical mechanics, while four-dimensional Lorentzian manifolds model space-time in general relativity..."
Chris
G'day
Manifolds and their formation hold the key issues in how space bodies contract and expand.
I have been reading on this subject for donkeys years, wiki talks about Higgs Mechanism, supersymmetry and superconductors in trying to explain matter that can create spins that may lead to manifolds of various forms.
I still have 2 years of reading, but the more I read it seems there is an endless journey.
Manifolds and their formation hold the key issues in how space bodies contract and expand.
I have been reading on this subject for donkeys years, wiki talks about Higgs Mechanism, supersymmetry and superconductors in trying to explain matter that can create spins that may lead to manifolds of various forms.
I still have 2 years of reading, but the more I read it seems there is an endless journey.
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