Dark Energy May Lurk In Hidden Dimensions 164
Magdalene writes in to let us know about a sketch of an idea, that might one day become a theory, to explain the dark energy that is making the universe flee faster and faster apart. It posits that dark energy may be the result of a new kind of neutrino wandering in tiny extra dimensions above our familiar three. She adds, "There is no word yet on whether Sphere or Square are available for comment." From the article: "The mysterious cosmic presence called dark energy, which is accelerating the expansion of the universe, might be lurking in hidden dimensions of space. This idea would explain how the dimensions of space remain stable — one of the biggest problems for the unified scheme of physics called 'string theory'... To get the same amount of acceleration seen by astronomers, Greene and Levin calculate that the extra dimensions should have a scale of about 0.01 millimeter."
New Scientist (Score:5, Insightful)
Sorry, nevermind.
Re: (Score:2)
Re:New Scientist (Score:5, Informative)
Well... (Score:5, Funny)
What's 122 orders of magnitude between friends?
Re: (Score:3, Funny)
That'd certainly get you to Kevin Bacon a few times.
Re: (Score:2)
Re: (Score:2)
Huh? (Score:3, Funny)
Re: (Score:1, Interesting)
Holly's wood? (Score:1)
Land of the Giants (Score:2)
So this explains Land of the Giants [imdb.com]
Re: (Score:1)
"Sphere or Square" reference... (Score:5, Informative)
It's a wonderful bit of British satire and more written by Edwin A. Abbott around 1884. Check it out - it's a wonderful short story, and a very nice example of the treasures that lie within the public domain.
Ryan Fenton
Re: (Score:3, Interesting)
I haven't read that one but I loved The Planiverse [amazon.com]
Re: (Score:2)
Re: (Score:2)
I have this version (signed, shipped direct from publisher through Amazon.com) but have not watched it yet. I do however note that it is published on single-layer DVD-R and not a pressed DVD. That would mean n
0.01 millimeter? (Score:1)
0.01 millimeter? Holy shit, if you step on a bug, you may be unwittingly killing an entire company just like Microsoft or SCO. I weepeth with remorse.
Re: (Score:2)
Re: (Score:1)
Re: (Score:3, Interesting)
That's actually a very interesting result, as it's on a similar scale to some other theories of large hidden dimensions. Doesn't mean it's right, but it's at least interesting when multiple theories arrive at similar results coming from different angles.
Now that... (Score:3, Interesting)
There is nothing worse than a scientist who fixes the observation to meet their theory, to paraphrase the illustrious but equally fictional Sherlock Holmes.
Bunk. (Score:1)
Re: (Score:2)
Re: (Score:2)
If he knows so much better than they do then why doesn't he get up and fix the theory? If he can't maybe he should take a little more humble attitude towards the people who are actually trying.
I'm not even sure what you should do. Lay off the coffee maybe. Or have some. Or get more sleep.
Re: (Score:2)
You and the original poster have the same problem. You THINK you know what's true and what isn't. Except you admit that you don't actually know enough to follow up on your own suggestions. So really you're just cranky know-it-alls who get snappy when someone calls you on it.
Those who can't do should be moderate in their criticism. The scientists in this story, as well as others, are trying to "fix the theory." Extra dim
Re: (Score:3, Informative)
Hm... That's a really very tough one. First of all, take dark matter... I can count 7 (much-publicized) theories off the top of my head. Which one are you going to fix?
Second. Well, there has been a few theories about dark energy but none of them have been greatly publicized. The truth is they are more whackier than dark matter theories. Now, you are suggesting that we go and fix the errors in them?! Huh? We dont even know which one is the one that matches reality most closely.
Third. Yes, astrophysici
Re:Now that... (Score:4, Insightful)
1. They are trying to fix the theory. Note that this does not automatically implie their results/ideas are right nor that I am defending them. I always found the whole "large extra dimesions that are just small enough so we haven't observed them but will at the LHC,..." thing total nonsense.
2. As clearly explained in TFA these should be observable in the near future. On the other hand, a theory of everything (if it does exist) is bound to at least have some features that are unobservable. Reproducing the big-bang, or some equivalent singular event near the origin of the universe is probably impossible.
(I am a former string theorist, which does not imply I am a believer)
Re:Now that... (Score:4, Interesting)
What part of such an LHC-observation scenario do you find as "total nonsense"? Afterall, physics (especially the LHC) needs two things: 1) a multitude of theories to debunk and 2) money. There are theorists which will "die" if the LHC does not observe large extra dimensions. So most such theorists say: "if this theory is correct, then large extra dimensions must be small enough so that we havent observed them before but are large enough to be observed at the LHC." I can see nothing that can be called total nonsense here -- as long as the clause "if this theory is correct" is included.
And I am an experimentalist. With very little taste for things that theorists believe to be true. So there you go... I spend my days hoping to reproduce a mini-singularity one day... ;)
Re: (Score:1)
2. My feeling that it is "total nonsense" is to some extend a feeling (as long as there is no proof or disproof, one is allowed such an opinion right?). On the other hand, I have read some of the key articles, seen some of these p
Re: (Score:2)
On the other hand, even if these relatively large extra dimensions exist, the theorists involved like giving it a zest of "we might find evidence of this real soon" by cranking down the potential size until where is just not detectable today but will be at the LHC. AND they do this without any motivation at all.
The motivation is that larger dimensions would have been seen already. There's nothing wrong with that. Eventually the size might be cranked down so far that the theory can't do the job it was invented to do, and then it would be in trouble.
A good motivation to me would be: well if we put the size to this or that we can reproduce (parts of) the standard model.
Or, if we put the size to this or that we can solve dark energy?
Large extra dimension theories can already reproduce the Standard Model. The point is to explain some puzzling features that the Standard Model has (such as the hierarchy problem) and to avoid predictin
Re: (Score:2)
Re: (Score:2)
...dark energy has fallen into an interdimensional rift in the fabric of space/time, can we shove the astrophysicists who insist on inventing the unobservable to fix their theories in with them
Extra dimensions aren't "unobservable", insofar as they have experimentally observable consequences. Dark energy may be one of them. There are other consequences for high energy particle physics and for the short distance behavior of gravity. All of these are currently being investigated to see if the extra dimension idea holds up.
and get on with fixing whatever the error in the models really is?
How do you know the error in the models is that they don't have extra dimensions?
There is nothing worse than a scientist who fixes the observation to meet their theory
Are you suggesting that astronomers have faked the observational data regarding dark energy
evil invader (Score:2, Funny)
I've seen Bush called a lot of things, but this takes the cake
Re:evil invader (Score:4, Funny)
I'm sorry, you seem to have the wrong thread. Mindless flames are over here [slashdot.org]
Acid (Score:5, Funny)
Oh yea.. (Score:2, Funny)
I wonder what inspired all of this thinking? (Score:2)
http://www.theonion.com/content/node/29433 [theonion.com]
Re: (Score:1)
We all know where Dark Energy comes from... (Score:5, Funny)
Next article, please!
(WIAK's Law: The longer a Star Wars discussion goes on, especially on Slashdot, the greater the likelyhood that someone mentions either Han shooting first or George Lucas raping their childhood.)
Re: (Score:1)
Re: (Score:3, Insightful)
erp...
Somebody's gonna do it... might as well be me... (Score:2)
Han raped my childhood first, you insensitive clod!
Consider Natalie Portman, Soviet Russia, and our new overlords included by reference.
How does a dimension have a scale? (Score:1)
Re: (Score:3, Insightful)
A telephone wire looks one dimentional from a distance, but up close there are ants walking on it's 2D surface.
Re: (Score:2)
Re:How does a dimension have a scale? (Score:4, Informative)
Re: (Score:2, Informative)
Re: (Score:2, Interesting)
dimensions, manifolds etc. (Score:5, Informative)
We don't actually need 2-dimensional euclidean space to describe the topological structure of the circle.
There are several different concepts of dimension in mathematics. The one you are probably thinking of is the dimension of a vector space. What we seem to need here is the dimension of a manifold. Intuitively, a n-dimensional manifold is something that locally "looks like" our familiar n-dimensional euclidean space (R^n). You already got that right with the ant example.
Manifolds can be described in different ways. One way is as a certain kind of subset of some higher-dimensional vector space R^m, this is the way you are probably imagining. But it is also possible to describe a manifold without any reference to a surrounding space.
For this we need the concept of a topological space. Informally, a topological space is a set in which we can talk about connectedness, continuity and which sets of points are "a neighborhood" of a given point.
As a topological space, the circle can be seen as the usual interval [0,1] (of real numbers), but with the points 0 and 1 identified (that is, they are considered to be the same point) (usually one would use the analogy "0 and 1 glued together", but this would evoke the intuition of a surrounding space again, which we are trying to avoid
Likewise, topologically a sphere is equivalent to a square (or a disk) with the whole boundary[1] considered to be a single point. A torus is a square with every point on the left edge identified with the corresponding point on the right edge, and every point on the top edge identified with the corresponding point on the bottom edge.
Generally, a n-dimensional topological manifold is defined as a topological space with the following property (+ some technical conditions):
For every point on the manifold, you can find a small region U around the point (a "neighborhood"), such that U is topologically the same ("homeomorphic") as a disk/ball or a box[2] in n-dimensional euclidean space. A homeomorphism is essentially a map f which puts the points of one space into one-to-one-correspondence with the points of another space, and respects convergence in the sense that some sequence[3] x_n converges to x if and only if f(x_n) converges to f(x). It can't tear regions apart which are connected, or vice versa.
For example, if we have some point of the sphere, we can take a small neighborhood U of it and map U to a disk in the obvious way. This mapping respects convergence. Thus, the sphere is a 2-dimensional topological manifold.
Now I only described the topological structure; topology is "qualitative" and doesn't talk about concrete distances, angles etc.. If you want to have these, you need a structure called a Riemannian manifold. But I haven't taken a course on differential geometry yet, so I won't talk about that
I hope I didn't tell you things you already know and that I didn't sound condescending. You are asking good questions and I think you would like topology courses
Whether the surrounding spaces are "real" is a matter of philosophy, but as you can see they are not absolutely necessary...
[1]: For the topologists: I'm using "boundary" in the informal sense here; of course the boundary (in the formal sense) of the whole space is always empty.
[2]: Actually it doesn't matter whether you require it to be homeomorphic to a ball in R^n or to the whole R^n.
[3]: In general it's a net, not a sequence
I tried topology once... (Score:5, Funny)
4th Dimension (Score:2)
Re: (Score:2)
A second is roughly 299792.8 kilometres long.
Re: (Score:2)
Re: (Score:3, Informative)
The key word here is unbounded.
The extra dimensions are "compactified". That mean they are bounded.
Example of spaces with bounded dimension are the circle or sphera. They both have maximum diameter - that mean the distance between the points of t
Re:How does a dimension have a scale? (Score:5, Informative)
Hi, I'm a first year graduate student in Physics, so I probably understand string theory at just about the right level to explain the basics. If I knew any more about it, I would be smart enough to not try to explain it. If I knew any less, I couldn't explain it at all. This will all make a lot more sense if you've ever studied complex numbers. If you haven't, here's your chance to start!
First, you need to understand the geometry of regular spacetime in Einstein's Special Relativity, which isn't the Euclidean geometry with several real coordinates that you learned about in high school school. The time coordinate is a regular real variable, just like in Euclidean geometry. But the space coordinates are three different imaginary units whose square is 1, call them i, j and k. A point in spacetime is characterized by 4 coordinates, like (1t, ix, jy, kz). This system is called the hyperbolic quaternions, or Minkowski space. Why hyperbolic? Read on!
Next, how do you calculate distance in spaces with imaginary coordinates? Recall from high school geometry that in a plane with 2 real coordinates, the distance between the origin (0,0) and a point P=(1x,1y) is d^2 = x^2 + y^2 = P dot P. In imaginary coordinates you do it a little differently, you take the dot product of P with P*, P* being the complex conjugate of P, and the dot product being multiplication of only the corresponding coordinates. Complex conjugation leaves the real coordinate unchanged but flips the sign on the imaginary coordinates, so 1 goes to 1, i to -i, j to -j, k to -k. Now the distance between the origin (0,0,0,0) and a point P=(1t, ix, 0, 0) is d^2 = (1t,ix,0,0) dot (1t,-ix,-0,-0) = 1^2 t^2 + (-i)(i)x^2 = t^2 - i^2 x^2, but i^2 = 1, so we have just d^2 = t^2 - x^2. In general we have d^2 = t^2 - x^2 - y^2 - z^2. Note that different points can be distance zero from each other. These points lie on each other's "light cones" because photons travel along these zero distance trajectories. Points with positive distance from each other are called timelike with each other and can have a cause and effect relationship. Points with negative distance are called spacelike with each other and are totally disconnected.
Now we're ready to see why this geometry is called hyperbolic! What are the points which are distance 1 from the origin? Let's use the distance equation with 1 for the distance, ignoring y and z to keep the math simpler . Then 1 = t^2 - x^2, that's just a hyperbola with two branches, one in the past and one in the future! These hyperbolae go on forever and therefore so does this kind of space. This hyperbolic spacetime stuff is why objects become distorted at high relative velocities. The two spherical gold nuclei that they smash together at the relativistic heavy ion collider see each other as flat hyperboloidal pancakes.
Ok, now we're finally ready to look at these small circular dimensions. Now we use a real coordinate for time and imaginary coordinates for space, just like before. However, this time we use the normal imaginary unit whose square is -1, not 1. It's usually called i, but I've already used i, so let's just call it u. Now the distance from the origin (0,0) to a point P (1t,ux) is P dot P* = 1^2 t^2 + (u)(-u) x^2 = t^2 - u^2 x^2, but u^2 = -1, so d^2 = t^2 + x^2. The minus has become a plus! What are the points which are distance 1 from the origin? 1 = t^2 + x^2, the equation of a circle! The circumference of this unit circle gives a characteristic length to this space, usually taken to be something like the Planck Length of 1.6 x 10^-35 meters.
In string theory, spacetime becomes the product of our familiar and beloved big, hyperbolic spacetime with a bunch of these small, circular spacetimes. Particles with electric charge go around in a circle, particles with weak nuclear charge fly around on a sphere, and particles with color like quarks and gluons move around on a hypersphere. Mass is related to the size of the particle in these circular spaces, with bigger particles being lighter. When he tal
Re: (Score:2)
Really simple, right?...
Except for the math, the concepts are simple. For this we have computers.
But being a freshman your not stuck into one theory or another yet, lets examine this statement of theirs for your thoughts:
The mysterious cosmic presence called dark energy, which is accelerating the expansion of the universe. ...
I have never understood this expanding universe theory at all. The universe expanding in all directions would also make us the center of it. Not likely, as that makes as much s
Simple... (Score:2)
That word you keep using. I do not think it means what you think it means. ;-)
Re: (Score:2)
Erm, sorry if this is a stupid question, but if their squares are 1, what makes them imaginary?
Re: (Score:2)
This makes these numbers imaginary...
Cheers!
--
Vig
Re: (Score:1)
That'd be circumference. A circle cannot have diameter unless it is embedded in some larger space which fills it. But then you have yet another dimension to explain away in the theory...
so...is this how it works? (Score:1)
I'm telling you... (Score:4, Informative)
Seriously: without some experimental evidence to back up these theories, they aren't worth the paper they are written on.
Re: (Score:1)
Re: (Score:1, Insightful)
Theory is just a word. Successes in physics have always been foreshadowed by thought experiments, wild conjectures, whatever. Empiricism on its own can't do it, and never could.
We often imagine technology before we have it. This calls for radical imagining outside our normal experience. Experiment can come before or later.
Quantum physics and General Relativity still sound incredible and fantastic to lay people
Re: (Score:2)
"A THEORY in technical use is a more or less verified or established explanation accounting for known facts or phenomena: the theory of relativity. A HYPOTHESIS is a conjecture put forth as a possible explanation of phenomena or relations, which serves as a basis of argument or experimentation to reach the truth: This idea is only a hypothesis."
You were saying? Those successes you mention were deemed successes because they were bolstered by emperical evidence, not more math.
Funniest title ever (Score:4, Interesting)
So.. let me get that straight. We solve the problem of energy we can't detect and dimensions we can't prove exist? Simple! We tuck the one into the other and thus explain everything in a single shot. Brilliant!
Now allow me walk away for today as I am laughing my guts out.
Re: (Score:2)
Re: (Score:2)
Did you just say a *non-spatial* dimension has a.. spatial dimension? Doesn't make sense does it. The "it's very thin" theory for extra dimensions is pure snake oil in my opinion.
If there are ever phenomenons like perception of time that they unwittingly described as dimensions to make the bottom line on their expressions, they are definitely not spatial. If they were spatia
Re: (Score:2)
We solve the problem of energy we can't detect and dimensions we can't prove exist?
We can detect dark energy — that's how we know it exists, because of its influence on gravitational phenomena. We just can't, currently, measure those influences well enough to narrow down the possibilities for its origin.
We can't prove anything in science, but we can find evidence to support a theory. Extra dimensions have experimental consequences; dark energy may be one of them. There are other ways that the existence these extra dimensions can be probed, especially in the case of the so-called
Re: (Score:2)
Half the scientists attribute this to a formula error. I wouldn't be so quick to take some uknown offset in energy for... a bunch of extra dimensions with dark energy lurking in them.
It's just too cheap of a cop out. The "fraction of a milimeter dimensions" don't make sense to me. If these dimensions have some sort of limited dimensions, it means spatial must have some too. Which screws up with the
Re: (Score:2)
Half the scientists attribute this to a formula error.
No. It's an observed phenomenon, it doesn't have anything to do with theoretical formulas.
I wouldn't be so quick to take some uknown offset in energy for... a bunch of extra dimensions with dark energy lurking in them.
Extra dimensions is just one theory of dark energy, and not even the most popular. There are plenty of others. And what is observed is not just an "unknown offset in energy", but an accelerating expansion of the universe. Normal kinds of energetic fields can't do that: they only make the expansion slow down because they gravitate. That's why dark energy is fundamentally different.
It's just too cheap of a cop out.
It's not a cop out, it's a the
Crackpot?? (Score:3, Insightful)
Actually untrue, unfortunately (Score:5, Insightful)
Unfortunately there is often just enough truth in some crackpot ideas to keep people pursuing them. We do have biological cycles which are influenced by the Moon (astrology), there probably are some numerological bits of weirdness in the Bible -it would be amazing if there weren't given the range of authors and their interests - and Freud had some genuine insights. It's this that can help to draw in intelligent and curious people.
Re: (Score:2)
There are numerological bits of weirdness everywhere if you want to find them. Remember these words of wisdom:
Re: (Score:2)
String Theory unfortunately has all the hallmarks of a belief system which, because we do not currently have the ability to falsify its predictions, lends itself to being entirely wrong.
String theory isn't any more of a belief system than any other idea about particle physics beyond the Standard Model. Post-SM physics theories that we can't yet falsify are a dime a dozen, and are in no way limited to string theory. There always will be, given the vast gulf between what we can probe and the highest energies possible to probe. That doesn't mean that none of those theories can be tested, that they can't have experimental consequences at energy levels we can probe. There are specific stri
Re: (Score:2)
String Theory unfortunately has all the hallmarks of a belief system which, because we do not currently have the ability to falsify its predictions, lends itself to being entirely wrong.
Keep in mind, even if string theory is wrong, it's wrong in
Re: (Score:2)
As a case in counterpoint, Newton devoted at least as much of his research to alchemy as he did to the "non-crackpot" sciences.
Re: (Score:2)
Isaac Newton was into numerology and astrology.
I'm not saying String Theory is crackpottery, just that genius doesn't immunize one against crackpottery.
Einstein's equations in smiley formalism (Score:1)
New dimensions... as usual (Score:1, Funny)
Hidden Dimensions.... Riiiigghhht (Score:2)
Re: (Score:2)
The Bush administration's war against science... (Score:4, Insightful)
Blasting physicists (or any scientist) for speculating on unsolved, scientific mysteries is just an astounding step backwards intellectually and I'm afraid that as a society we've taken that huge leap backwards.
If the mob stopped spouting their own specious dogma, showing their own Newtonian-based cognitive dissonance and actually RTFA:
That folks, is science in action. Don't make me go through the checks and balances between experiment and theory.
It stops being science when critical thinking and the scientific process are overruled by non-scientific reasons.
The corollary is that it stops being scientific criticism when the basis of the contrary views also fall prey to non-scientific reasonings. Reasonings such as "I don't see any _______" - fill in the blank with "atoms", "neutrinos", "monkeys giving birth to human babies" - all of which were used as arguments against theories about things we did not yet know and were considered unprovable at the time.
Well, I for one DO NOT welcome the creationist tagging overlords.
Re:The Bush administration's war against science.. (Score:2)
Re:The Bush administration's war against science.. (Score:2)
Re:The Bush administration's war against science.. (Score:2)
His Dark Materials (Score:2)
Kinda neat that science is mirroring fiction.
If only other jobs were this easy... (Score:2)
"Why is the project late?" - "Dark Time."
"What happened to all the donuts in the break room?" - "Um, sucked into a hidden dimension?"
Perhaps something else is happening. (Score:2)
Cosmological constant (Score:2)
re - Dark Energy May Lurk In Hidden Dimensions (Score:2, Interesting)
The real problem (Score:2)
All these st
Re: (Score:1)
Re:Nothing for you to see here. Please move along. (Score:5, Funny)
Re: (Score:1)
So our dearly-departed Fluffy is contributing the excelleration of the universe expension? Its gonna be hard to explain that one to my child.
Re:Being a non-Scientist (Score:5, Insightful)
Besides, there's nothing wrong with inventing something new to preserve some theory. The neutrino was "invented" to preserve conservation of energy. Antimatter was "invented" to keep quantum theory consistent with relativity.
Despite common memes about the history of science, the vast majority of new ideas don't require tossing out the old ideas.
You're being hypocritical to boot. MOND is also an invention of something new to try to save a theory. Dark matter introduces new kinds of matter to try to save our theory of gravity. MOND introduces a whole new theory of gravity to try to save the existing particles we know about. Arguably, the former is a more conservative choice than the latter! Of course, both modifications may be necessary, but right now it looks like you can do it all with dark matter, and there are already reasons coming from particle physics, independent of any astrophysical evidence, for why those kinds of dark matter particles should exist.
There is also nothing wrong with inventing a theory of quantum gravity, such as string theory, in order to save existing theories of relativity and quantum mechanics, since both of them have enormous amounts of evidence in their favor.
Continuing on string theory, the theory has not "failed", nor do people "add more strings" to fix it; indeed, the string content of the theory is determined by the overarching M-theory and cannot be adjusted at will.
Re: (Score:2)
Re: (Score:2)
To your specific question:
What is the relative percentage of scientists (in related fields) that believe in string theory compared to its alternatives?
it depends on what you mean by "related fields", and "believe in".
As a theory of quantum gravity: there are other theories of quantum gravity (e.g., loop quantum gravity, causal dynamical triangulations,
Re: (Score:2)
When you couple this to t
Re: (Score:2)