This is an easier one than dark matter vs. modified gravity. As mentioned, I’m going to be on Science Friday today, and they asked me to contribute a guest blog post, which I’m cross-posting below. Old news, I’m sure, for longtime CV readers, but here you go.
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Probably the biggest single misconception I come across in popular discussions of dark matter and dark energy is the accusation that these concepts are a return to the discredited idea of the aether. They are not — in fact, they are precisely the opposite.
Back in the later years of the 19th century, physicists had put together an incredibly successful synthesis of electricity and magnetism, topped by the work of James Clerk Maxwell. They had managed to show that these two apparently distinct phenomena were different manifestations of a single underlying “electromagnetism.” One of Maxwell’s personal triumphs was to show that this new theory implied the existence of waves traveling at the speed of light — indeed, these waves are light, not to mention radio waves and X-rays and the rest of the electromagnetic radiation spectrum.
The puzzle was that waves were supposed to represent oscillations in some underlying substance, like water waves on an ocean. If light was an electromagnetic wave, what was “waving”? The proposed answer was the aether, sometimes called the “luminiferous aether” to distinguish it from the classical element. This idea had a direct implication: that Maxwell’s description of electromagnetism would be appropriate as long as we were at rest with respect to the aether, but that its predictions (for the speed of light, for example) would change as we moved through the aether. The hunt was to find experimental evidence for this idea, but attempts came up short. The Michelson-Morley experiment, in particular, implied that the speed of light did not change as the Earth moved through space, in apparent contradiction with the aether idea.
So the aether was a theoretical idea that never found experimental support. In 1905 Einstein pointed out how to preserve the symmetries of Maxwell’s equations without referring to aether at all, in the special theory of relativity, and the idea was relegated to the trash bin of scientific history.
Aether was a concept introduced by physicists for theoretical reasons, which died because its experimental predictions were ruled out by observation. Dark matter and dark energy are the opposite: they are concepts that theoretical physicists never wanted, but which are forced on us by the observations.
Dark matter, in particular, is nothing at all like the aether. It’s something that seems to behave exactly like an ordinary particle of matter, just one with no electric charge or strong interaction with known matter particles. Those aren’t hard to invent; particle physicists have approximately a billion different candidate ideas, and experiments are making great progress in trying to detect them directly. But the idea didn’t come along because theorists had all sorts of irresistible ideas; we were dragged kicking and screaming into accepting dark matter after decades of observations of galaxies and clusters convinced people that regular matter simply wasn’t enough. And once that idea is accepted, you can go out and make new predictions based on the dark matter model, and they keep coming true — for example in studies of gravitational lensing and the cosmic microwave background. If the aether had this much experimental support, it would have been enshrined in textbooks years ago.
Dark energy is conceptually closer to the aether idea — like the aether, it’s not a particle, it’s a smooth component that fills space. Unlike the aether, it does not have a “frame of rest” (as far as we can tell); the dark energy looks the same no matter how you move through it. (Not to mention that it has nothing to do with electromagnetic radiation — it’s dark!) And of course, it was forced on us by observations, especially the 1998 discovery that the universe is accelerating, which ended up winning the Nobel Prize in 2011. That discovery took theoretical physicists around the world by surprise — we knew it was possible in principle, but almost nobody actually believed it was true. But when the data speak, a smart scientist listens. Subsequent to that amazing finding, cosmologists have made other predictions based on the dark energy idea, which (as with dark matter) keep coming true: for the cosmic microwave background again, as well as for the distribution of large-scale structure in the universe.
There is still much we don’t know about dark matter and dark energy; in particular, we certainly haven’t nailed down what exactly they are (although we have many plausible ideas), and the only way we’ve detected them is indirectly, through their effects on gravitational fields in the universe. But they are not arbitrary; both ideas make very specific predictions for what those gravitational effects should be, which astronomers have tested and verified. Unlike the aether, which shrunk and eventually disappeared under experimental scrutiny, the case for dark matter and dark energy continues to grow stronger.
Well, my favorite theory of everything is Mills’ Grand Unified Theory of Classical Physics.
http://www.blacklightpower.com/theory-2/theory/
Gets rid of almost all the goofiness of quantum theory (particles acting instantaneously over great distances, a single photon existing in many places at the same time, etc…), and restores physics to something deterministic again, with real physical meaning and not mathematical nonsense.
He says dark matter is hydrogen with the electron orbiting below the “ground state” predicted by current quantum mechanics; he calls such an entity a hydrino. He claims a new energy source from hydrogen reducing to this lower energy state that does not interact much with other matter. So yes, there are HUGE potential uses for dark matter – nearly unlimited energy, new chemistry and new properties of matter not even dreamed of yet, all of course if one believes dark matter is a hydrino as Mills theorizes.
@mpc, a simpler explanation of the double slit experiment is given by Mills:
http://www.blacklightpower.com/theory-2/theory/double-slit/
There is no aether.
@knov, the following is simpler and correct.
Aether has mass. Aether physically occupies three dimensional space. Aether is physically displaced by matter.
A moving particle has an associated aether displacement wave; analogous to the bow wave of a boat.
In a double slit experiment the particle travels a well defined path which takes it through one slit. The associated aether wave passes through both. As the aether wave exits the slits it creates wave interference. As the particle exits a single slit the direction it travels is altered by the wave interference. This is the wave piloting the particle of pilot-wave theory. Detecting the particle strongly exiting a single slit turns the associated aether wave into chop. The aether waves exiting the slits interact with the detectors and become many short waves with irregular motion. The waves become disorderly. The waves are disorganized. There is no wave interference. The particle pitches and rolls through the chop. The particle gets knocked around by the chop and it no longer creates an interference pattern.
As a layperson who naively/instinctively sees strong parallels between luminiferous aether and dark matter I think the whole basis of this article is wrong:
In both cases there is a theory at odds with observation, the proposal is to magic up out of thin air a compensatory mechanism.
In the case of the aether this mechanism has been discredited, in the case of the dark matter it is under review.
Maybe the evidence for the existence of dark matter is becoming overwhelming but as a lay observer I don’t yet get this sense.
“It’s probably better to clarify that it’s expansion of the universe that is accelerating.”
Why? If a car is accelerating, I say the car is accelerating. I don’t say the motion of the car is accelerating, nor that the velocity of the car is accelerating, neither of which make any sense.
Ann Kittenplan: What has been disproven is a stationary aether and a completely entrained aehter. The aether is neither. Aether is displaced by matter.
Don’t fall for the lazy nonsense of mainstream physics.
@ Philip Helbig
An accelerating car does not expand. Its length decreases.
The following is an animation of a moving particle and its associated aether wave.
http://www.youtube.com/watch?v=iWRNZNemQyY
The original post is a very narrow view of the “aether” concept, limiting it to a specific and rejected version of it with a fixed frame of reference considered in relation to Maxwell’s equations.
But, a broader sense of the term “aether” is also possible. In a broad sense, it represents the conclusion that “empty space” is not just “nothing,” but has definable properties like local space-time curvature, a possible minimum scale (perhaps the Planck scale), dimensionality, a speed limit for contained particles, vacuum energy, dark energy, locality (or non-locality), causality (or select exceptions to causality), an arrow of time, etc.
It is quite possible, within the range of observational data, that another property of space-time may be maximum local energy density (nothing ever observed has had more mass-energy density than a neutron star, if one is willing to acknowledge a certain amount of quantum uncertain that “smears” the effective matter-energy density of point particles over sub-Planck distances, and to assign an average value based on total mass divided by volume within event horizons to singularities).
A difference of opinion regarding aether pretty much boils down to different people using different definitions of the term, both of which are admitted as viable in the ever pliable English language, without acknowledging this fact.
General relativity, standard model quantum mechanics, dark energy cosmology, loop quantum gravity, string theory, modified gravity theories, and almost every other remotely mainstream theory in physics established or seriously examined by physicists, assigns some sort of properties to “empty space”, even if a fixed frame of reference turns out not to be one of those properties, and hence adopt aether-like concepts in the broader sense. In modern physics, vacuums aren’t truly empty.
I prefer the broader definition and would be inclined to say that a certain kind of aether was rejected – the kind with a fixed reference frame, rather than the notion that empty space itself is something that has properties itself, that is at the real core of the term. But, your preferences may vary, and wouldn’t cause conflict if all participants disclosed the sense in which they were using the term.
The following analogues seem to me much more relevant:
Aether and SUSY: A purely theoretical construct that theorists cling to, despite mounting experimental counter-evidence. Never, never, never give up.
Dark matter/energy and epicycles: Fudge factors necessary to reconcile experiments with the prevailing theoretical paradigm.
@60: Show us a better theory which fits the observations.
@Phillip Helbig: Aether has mass and physically occupies three dimensional space. Aether is physically displaced by matter. There is no such thing as non-baryonic dark matter traveling with matter. Matter moves through and displaces the aether.
Einstein’s definition of the state of the aether:
“the state of the [ether] is at every place determined by connections with the matter and the state of the ether in neighbouring places”
The state of the aether at every place determined by connections with the matter and the state of the aether in neighboring places is the state of displacement of the aether.
Displaced aether pushing back and exerting inward pressure toward matter is gravity.
A moving particle has an associated aether displacement wave. In a double-slit experiment, the particle travels a well defined path which takes it through one slit while the associated aether wave passes through both.
The Michelson-Morley experiment disproved a stationary aether the Earth moved through. The Sagnac effect disproved a completely entrained aether. The aether is neither stationary nor completely entrained by the Earth. Aether is displaced by matter.
‘NASA’s Voyager Hits New Region at Solar System Edge’
http://www.nasa.gov/home/hqnews/2011/dec/HQ_11-402_AGU_Voyager.html
“Voyager is showing that what is outside is pushing back. … Like cars piling up at a clogged freeway off-ramp, the increased intensity of the magnetic field shows that inward pressure from interstellar space is compacting it.”
It is the aether which is displaced by the matter the solar system consists of which is pushing back and exerting inward pressure toward the solar system.
‘Surprise! IBEX Finds No Bow ‘Shock’ Outside our Solar System’
http://www.universetoday.com/95094/surprise-ibex-finds-no-bow-shock-outside-our-solar-system/
‘“While bow shocks certainly exist ahead of many other stars, we’re finding that our Sun’s interaction doesn’t reach the critical threshold to form a shock,” said Dr. David McComas, principal investigator of the IBEX mission, “so a wave is a more accurate depiction of what’s happening ahead of our heliosphere — much like the wave made by the bow of a boat as it glides through the water.”’
The wave ahead of our heliosphere is an aether displacement wave. This is evidence of a moving ‘particle’, the solar system, having an associated aether wave.
‘Hubble Finds Ghostly Ring of Dark Matter’
http://www.nasa.gov/mission_pages/hubble/news/dark_matter_ring_feature.html
“Astronomers using NASA’s Hubble Space Telescope got a first-hand view of how dark matter behaves during a titanic collision between two galaxy clusters. The wreck created a ripple of dark mater, which is somewhat similar to a ripple formed in a pond when a rock hits the water.”
The ‘pond’ consists of aether. The moving ‘particles’ are the galaxy clusters. The ripple is an aether displacement wave. The ripple is a gravitational wave. This is also evidence of a moving ‘particle’, the galaxy clusters, having an associated aether wave.
‘Giant black hole kicked out of home galaxy’
http://www.astronomy.com/en/News-Observing/News/2012/06/Giant%20black%20hole%20kicked%20out%20of%20home%20galaxy.aspx
“But these new data support the idea that gravitational waves — ripples in the fabric of space first predicted by Albert Einstein but never detected directly — can exert an extremely powerful force.”
The fabric of space is the aether.
Gravitational waves are ripples in the aether.
What ripples when galaxy clusters collide is what waves in a double slit experiment; the aether.
Einstein’s gravitational wave is de Broglie’s pilot-wave.
They are both aether displacement waves.
The common astrophysicists/astronomers’ claim that dark matter is the aether of the 21st century is rather accurate.
The aether was theoretically postulated to account for certain observations. It was never found in direct experiments. In fact, experimental results were in contradiction with aether predictions.
Dark matter was theoretically postulated to account for certain observations. It has been never found in despite of hundred of direct experiments made up to the date. There exists a broad range of experimental results and observations in disagreement with the dark matter model.
Indirect observations as gravitational lensing do not count as “experiments that support dark matter”, because the same lensing is explained by theories without appealing to any hypothetical dark matter.
@Pinger & Bill
I may get some details wrong (and I apologise in advance if I overly simplify the issue), but if I understand your question, you are asking why the Bullet Cluster (and other galaxies and clusters) have some structure to the dark matter in them (ie they aren’t uniform or points)?
The universe isn’t uniform because dark matter does clump. It still experiences gravity (and maybe the weak force). This means any slight deviations from a uniform background in how it is was distributed originally gets amplified over time.
However, it isn’t uniform because it gets angular momentum from these same deviations.
If you have a piece of dark matter, it moves towards these already denser regions as they have stronger gravity. However, as it falls the attraction to rest of the dark matter gives it angular momentum, which means it misses the center slightly. Normal matter does this as well, however, it can get rid of some of this angular momentum through radiation and by colliding with other bits of material. Dark matter doesn’t collide, and doesn’t give off radiation so it keeps on orbiting this dark matter clump. This is similar to the planets around the sun (although we are in a disk because we were able to collide and radiate some of this energy away before the planets formed, so it is like a set of planets without a disk) or stars inside an elliptical galaxy.
The too long; didn’t read summary is: It does clump, however, it can’t get rid of what angular momentum it gets when it first starts clumping so it doesn’t collapse into a black hole.
Possibly the best visual examples of (simulations of) this clumping are available here http://www.mpa-garching.mpg.de/galform/data_vis/ which shows the Millennium Simulation and how we think the dark matter will look in these structures.
@MNichols Dark matter does not clump. Dark matter has been shown to be smoothly distributed throughout dwarf galaxies.
What is mistaken as the clumping of dark matter is the state of displacement of the aether.
Maxwell equations predict correct speed of light only when it is assumed that light is traveling through a medium with characteristics of a perfect solid. Am I correct in thinking that this should inform us regarding the nature of dark matter?
It informs you regarding the nature of the aether. Maxwell’s displacement current is a displacement of the aether.
Aether has mass. Aether physically occupies three dimensional space. There is no such thing as non-baryonic dark matter traveling with matter. Matter moves through and displaces the aether.
‘Superfluid Is Shown To Have Property Of A Solid’
http://www.sciencedaily.com/releases/1999/07/990730072958.htm
“Northwestern University physicists have for the first time shown that superfluid helium-3 — the lighter isotope of helium, which is a liquid that has lost all internal friction, allowing it to flow without resistance and ooze through tiny spaces that normal liquids cannot penetrate — actually behaves like a solid in its ability to conduct sound waves.”
The aether is, or behaves similar to, a superfliud with properties of a solid; an incompressible fluid.
Perhaps the Mill’s hydrino referred to by Knov above has the necessary characteristics; dark, superfluid, and properties of perfect solid.
“But the CBR does give a rest frame for the universe. ”
Misleading. The issue of preferred frames is whether you have the same laws in all frames, or whether your laws in their form pick out one of them. It has nothing to do with whether (for example) you can identify a center of momentum frame for the visible universe.
Superfluid with properties of a perfect solid is the definition of the aether.
There is no such thing as non-baryonic dark matter traveling with matter.
Matter moves through and displaces the aether.
Why don’t you take the theory of an “aether” ( I hate that spelling ) and just use a different name if you really believe in it that much? You know the scientific community will never, ever, ever, ever, ever accept an aether. So why are you still calling it that?
Do you know when you can spot a crackpot? When they say the exact same comment over and over again. Physics crackpots tend to hijack a remedial level popular science blog while claiming that they have the answers to all our problems; if only someone would listen. mpc755, if you believe so deeply in it, then why are you not professionally pursuing it? Why aren’t you a physicist? why aren’t you writing detailed scientific papers about it and proving it beyond a shadow of a doubt? because your a crackpot, and unfortunately, any crackpot can post a comment online free for anyone to post to. I’m doing it right now.
@meh Why aren’t you able to understand what is presently postulated as non-baryonic dark matter is aether? Why aren’t you able to understand there is no such thing as non-baryonic dark matter traveling with matter? Why aren’t you able to understand matter moves through and displaces the aether.
From the ‘sloshing’ back and forth detected when galaxy clusters collide to the offset between light lensing through the space neighboring moving galaxy clusters and the galaxy clusters themselves, to the wave out ahead of our heliosphere being analgous to the bow wave of a boat, and on and on and on is the evidence of the aether.
Einstein stated, “According to the general theory of relativity space without ether is unthinkable”. How are you able to interpret that to mean there isn’t an aether? What if Einstein had said ‘space with ether is unthinkable’. Would that have meant there is an aether in relativity? Of course not. How is it when Einstein specifically states there is an aether in relativity you are able to interpret that as there is no aether?
How did mainstream physics get so screwed up as to insist there is no aether when ALL of the evidence IS evidence of the aether?
Only someone who has been completely intellectually and logically defeated answers questions with questions. Do you know how many people like you there are on all the science blogs out there? I didn’t say I don’t accept an aether, I asked why are you so hell bent on picking a fight about it? because the way you are presenting the case for an aether, draws zero interest. When has the following argument ever persuaded anyone: You know that thing you absolutely refuse to believe, well I believe it, so you should too.
DUDE, they refuse to believe it for one reason or another. You don’t understand how simple human communication works; THAT’s why you’re a crackpot!
Another way to tell you’re a crackpot is because you’re assuming that everyone is arguing with you. I’m telling you that 99% of physicists don’t believe in an aether. I’m not saying I don’t believe in it, I’m stating facts.
AND AGAIN, if you believe in it so much, why aren’t you pursuing it professionally? The answer is because you know you don’t have the guts or the intellect to do so. You probably know nothing about math and what you know about physics you read online. Yet despite your gross ignorance of the basics, you think that typing a comment on a popular science blog will definitely convince everyone who matters; these words you type will certainly change the world and it will be forever imbedded to a hard drive on a server. What could possibly change about our technology in 100 years? We’ll certainly always use the same method of data storage linked to the internet, right? Our method of transmitting information over the internet to various computers all over the world will certainly never ever change.
DUDE, why are you unable to understand there is no such thing as non-baryonic dark matter which travels with matter? Why are you unable to understand matter moves through and displaces the aether?
AND AGAIN, why are you unable to understand displaced aether pushing back and exerting inward pressure toward matter is gravity, a moving particle has an associated aether displacement wave and in a double slit experiment the moving particle travels a well defined path which takes it through one slit while the associated aether wave passes through both?
You know, back in the 1970’s there was a musical group with the name “5th Dimension”…
“Pay no attention to the man behind the curtain!” – OZ the Incredible