The Dark Universe

[Slammr (imported)]

The Universe is a strange place, stranger than we can imagine.

http://www.sciencemag.org/content/302/5653/2038.full

WMAP (http://map.gsfc.nasa.gov/)

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Illuminating the Dark Universe

Charles Seife (http://www.sciencemag.org/search?author ... mit=Submit)

#1 The Winner

Portraits of the earliest universe and the lacy pattern of galaxies in today's sky confirm that the universe is made up largely of mysterious dark energy and dark matter. They also give the universe a firm age and a precise speed of expansion.

See Web links on Cosmology

A lonely satellite spinning slowly through the void has captured the very essence of the universe. In February, the Wilkinson Microwave Anisotropy Probe (WMAP) produced an image of the infant cosmos, of all of creation when it was less than 400,000 years old. The brightly colored picture marks a turning point in the field of cosmology: Along with a handful of other observations revealed this year, it ends a decades-long argument about the nature of the universe and confirms that our cosmos is much, much stranger than we ever imagined.

Five years ago, Science's cover sported the visage of Albert Einstein looking shocked by 1998's Breakthrough of the Year: the accelerating universe. Two teams of astronomers had seen the faint imprint of a ghostly force in the death rattles of dying stars. The apparent brightness of a certain type of supernova gave cosmologists a way to measure the expansion of the universe at different times in its history. The scientists were surprised to find that the universe was expanding ever faster, rather than decelerating, as general relativity—and common sense—had led astrophysicists to believe. This was the first sign of the mysterious “dark energy,” an unknown force that counteracts the effects of gravity and flings galaxies away from each other.

Although the supernova data were compelling, many cosmologists hesitated to embrace the bizarre idea of dark energy. Teams of astronomers across the world rushed to test the existence of this irresistible force in independent ways. That quest ended this year. No longer are scientists trying to confirm the existence of dark energy; now they are trying to find out what it's made of, and what it tells us about the birth and evolution of the universe.

Lingering doubts about the existence of dark energy and the composition of the universe dissolved when the WMAP satellite took the most detailed picture ever of the cosmic microwave background (CMB). The CMB is the most ancient light in the universe, the radiation that streamed from the newborn universe when it was still a glowing ball of plasma. This faint microwave glow surrounds us like a distant wall of fire. The writing on the wall—tiny fluctuations in the temperature (and other properties) of the ancient light—reveals what the universe is made of.

Long before there were stars and galaxies, the universe was made of a hot, glowing plasma that roiled under the competing influences of gravity and light. The big bang had set the entire cosmos ringing like a bell, and pressure waves rattled through the plasma, compressing and expanding and compressing clouds of matter. Hot spots in the background radiation are the images of compressed, dense plasma in the cooling universe, and cold spots are the signature of rarefied regions of gas.

Just as the tone of a bell depends on its shape and the material it's made of, so does the “sound” of the early universe—the relative abundances and sizes of the hot and cold spots in the microwave background—depend on the composition of the universe and its shape. WMAP is the instrument that finally allowed scientists to hear the celestial music and figure out what sort of instrument our cosmos is.

The answer was disturbing and comforting at the same time. The WMAP data confirmed the incredibly strange picture of the universe that other observations had been painting. The universe is only 4% ordinary matter, the stuff of stars and trees and people. Twenty-three percent is exotic matter: dark mass that astrophysicists believe is made up of an as-yet-undetected particle. And the remainder, 73%, is dark energy.

The tone of the cosmic bell also reveals the age of the cosmos and the rate at which it is expanding, and WMAP has nearly perfect pitch. A year ago, a cosmologist would likely have said that the universe is between 12 billion and 15 billion years old. Now the estimate is 13.7 billion years, plus or minus a few hundred thousand. Similar calculations based on WMAP data have also pinned down the rate of the universe's expansion—71 kilometers per second per megaparsec, plus or minus a few hundredths—and the universe's “shape”: slate flat. All the arguments of the last few decades about the basic properties of the universe—its age, its expansion rate, its composition, its density—have been settled in one fell swoop.

As important as WMAP is, it is not this year's only contribution to cosmologists' understanding of the history of the universe. The Sloan Digital Sky Survey (SDSS) is mapping out a million galaxies. By analyzing the distribution of those galaxies, the way they clump and spread out, scientists can figure out the forces that cause that clumping and spreading—be they the gravitational attraction of dark matter or the antigravity push of dark energy. In October, the SDSS team revealed its analysis of the first quarter-million galaxies it had collected. It came to the same conclusion that the WMAP researchers had reached: The universe is dominated by dark energy.

This year scientists got their most direct view of dark energy in action. In July, physicists superimposed the galaxy-clustering data of SDSS on the microwave data of WMAP and proved—beyond a reasonable doubt—that dark energy must exist. The proof relies on a phenomenon known as the integrated Sachs-Wolfe effect. The remnant microwave radiation acted as a backlight, shining through the gravitational dimples caused by the galaxy clusters that the SDSS spotted. Scientists saw a gentle crushing—apparent as a slight shift toward shorter wavelengths—of the microwaves shining near those gravitational pits. In an uncurved universe such as our own, this can happen only if there is some antigravitational force—a dark energy—stretching out the fabric of spacetime and flattening the dimples that galaxy clusters sit in.

Some of the work of cosmology can now turn to understanding the forces that shaped the universe when it was a fraction of a millisecond old. After the universe burst forth from a cosmic singularity, the fabric of the newborn universe expanded faster than the speed of light. This was the era of inflation, and that burst of growth—and its abrupt end after less than 10−30 seconds—shaped our present-day universe.

For decades, inflation provided few testable hypotheses. Now the exquisite precision of the WMAP data is finally allowing scientists to test inflation directly. Each current version of inflation proposes a slightly different scenario about the precise nature of the inflating force, and each makes a concrete prediction about the CMB, the distribution of galaxies, and even the clustering of gas clouds in the later universe. Scientists are just beginning to winnow out a handful of theories and test some make-or-break hypotheses. And as the SDSS data set grows—yielding information on distant quasars and gas clouds as well as the distribution of galaxies—scientists will challenge inflation theories with more boldness.

The properties of dark energy are also now coming under scrutiny. WMAP, SDSS, and a new set of supernova observations released this year are beginning to give scientists a handle on the way dark energy reacts to being stretched or squished. Physicists have already had to discard some of their assumptions about dark energy. Now they have to consider a form of dark energy that might cause all the matter in the universe to die a violent and sudden death. If the dark energy is stronger than a critical value, then it will eventually tear apart galaxies, solar systems, planets, and even atoms themselves in a “big rip.” (Not to worry; cosmologists aren't losing sleep about the prospect.)

For the past 5 years, cosmologists have tested whether the baffling, counterintuitive model of a universe made of dark matter and blown apart by dark energy could be correct. This year, thanks to WMAP, the SDSS data, and new supernova observations, they know the answer is yes—and they're starting to ask new questions. It is, perhaps, a sign that scientists will finally begin to understand the beginning.

[moi621 (imported)]

No!

It is a sign that one can design an experiment to prove what they are out to prove. What is lacking is data review as may explain the results in another manner. Yes, such prejudices happen, even in the Name of Science.

So is light a particle or a wave, data supports both.

There must be a "dark photon" out there.

Dark Matter/Energy like the multiverse seem like mathematical games as opposed to genuine observation.

Moi

String Theory anyone?

[tjstill (imported)]

No!

It is a sign that one can design an experiment to prove what they are out to prove. What is lacking is data review as may explain the results in another manner. Yes, such prejudices happen, even in the Name of Science.

So is light a particle or a wave, data supports both.

There must be a "dark photon" out there.

Dark Matter/Energy like the multiverse seem like mathematical games as opposed to genuine observation.

Moi

String Theory anyone?

I really dont understand what you are trying to say. Could you give a bit more detail behind your "no" and what was wrong with the experimetal design that leads you to dismiss it?

From my understanding, you design an experiments to test out a hypothesis. If the experiment shows the hypothesis as being supported then the hypothsis stands until one that is better supported by the data is put forward.

Do you believe the data to be wrong and hence the hypothesis unsupported? Or do you believe the data is reasonably accurate but that the hypothesis put forward to be tested by the experiment was poor? In which case what hypotheisis are you aware of that is better supported by the data?.

In answer to you other questions, my current understanding is that light is light. It can be shown to have wave like properities and particle like properties but it resolutely refuses to be catogorised as either.

I am not sure why there must be a dark photon or what you would expect the properties of this to be. Photons are quite high energy and reasonably easy to detect. An analogous "dark photon" I would take to mean a photon that was similar to an anti photon this would be reasonably easy to detect in any interaction with other "particles". Dark matter is proving very difficult to detect because of its lack of interaction. On the small scale we have not been able to support the hypothesis for it existance. Only now that we can look at clearer data for large scale effects can we see the evidence for something that cannot be explained by current models.

The multiverse is a cosmological "model". It is put forward to test theories against and as you say these tend to be mathematicaly based . It helps to try to fit various experimental results into a model because if lots of different ones fit then the model can be considered useful as a tool to understanding. If few results fit then the model is of less use and may well fall out of favour. It is a mathematical game as you say, but it helps to see just how well the data fits together from various sources. As a reflection of reality I would say there is far too little supporting data for a multiverse to be considered as anthing other than an interesting possibility at the moment.

The evidence for dark matter and dark energy is much more persuasive now. There is experimental data available, of high quality, that does not fit well with any current model other than that which calls for this totaly counter intuitive dark stuff!

I expect people will dislike it because it is so bizzare and it will sound like crazy talk (as bad as quantum supositions) but if there were a more simple explanation of the data I am sure many scientists would be happy.

String theory is just a theory, its just a tool to test things to try to understand the results from high energy experiments (like in the hadron colider). It has little bearing on real life as we will experience it.

I bet scientists wish it was a lot simpler and did not have to worry about multi dimesions twisted in on themselves but when faced with weird observations (that are repeatable by others) and therefore look to be true, then you have only two choices. Try and find a model that fits or put you head in the sand... mumbling rubbish

[moi621 (imported)]

A dark photon would no more likely be an anti photon then

dark matter be anti matter.

I do believe in anti matter. I saw Tom Hanks in Angels and Demons.

I have seen what science programs as available regarding dark matter and dark energy. "Science" often gets mismanaged even in modern times and especially when you have a believer at the controls.

I find no compelling evidence of dark this or that then to explain, "missing matter". And the later seems like so much arithmetic.

I will do my best to read any upload as may convert me. Not a link. A personal rumination as to convince me of Dark Matter, etc.

Moi

[Slammr (imported)]

A dark photon would no more likely be an anti photon then

dark matter be anti matter.

I do believe in anti matter. I saw Tom Hanks in Angels and Demons.

I have seen what science programs as available regarding dark matter and dark energy. "Science" often gets mismanaged even in modern times and especially when you have a believer at the controls.

I find no compelling evidence of dark this or that then to explain, "missing matter". And the later seems like so much arithmetic.

I will do my best to read any upload as may convert me. Not a link. A personal rumination as to convince me of Dark Matter, etc.

Moi

We know dark matter exists, because if it didn't, galaxies would fly apart. There is not enough observable matter in them to keep them together, so the remainder has to be unobservable, dark, matter. Dark matter CANNOT be antimatter. Antimatter and matter annihilate each other when they come together. If Dark matter were antimatter, no matter would exist. It would all be annihilated. There would be no stars, planets, dust, or gas left in the Universe.

We also know dark matter exists because of gravitational lensing. Gravity bends light, so we can observe the presence of dark matter by observing how light from faraway places in bent by the presence on dark matter.

By measuring the motions of stars and gas, astronomers can "weigh" galaxies. In our own system, we can use the velocity of the Earth around the Sun to measure the Sun's mass. We can use the same method to measure the "weight" of galaxies. The Sun moves around the Milky Way at 225 KM/sec. We can use this velocity and the velocity of other stars to measure the mass of our galaxy. We can measure the speed of stars in other galaxies to measure the "weight" of those systems. Without the weight of unobservable matter, the galaxies would fly apart. Stars in them rotate to fast around the galaxies for the matter, stars, gas, and dust, that we observe, to be all there is.

The presence of Dark Energy is needed to explain the distribution of galaxies in the Universe and why the Universe is expanding at an ever increasing rate. That 72% of the energy in the Universe is dark energy explains why the Universe appears to be flat rather than curved and why it is expanding at an accelerated rate. Dark energy has a gravitationally repulsive effect, and without it, the expansion of the Universe would be slowing down not speeding up as has been observed.

Without dark energy the Universe is curved and would expand, its expansion slowing, until it begins to contract, continuing to contract back to the point from which it began. Observation of the Universe says that won't happen. It will continue to expand for trillions of years, eventually dying a cold, dark, death, so if Man is around trillions of years from now, he will have to find a way to travel to another, younger, Universe to escape this one.

[moi621 (imported)]

Thank You

I will re read it a few times.

Gravitational lens makes sense, so why is it dark matter and not undiscovered matter?

Moi

[Riverwind (imported)]

It will continue to expand for trillions of years, eventually dying a cold, dark, death, so if Man is around trillions of years from now, he will have to find a way to travel to another, younger, Universe to escape this one.

Is it time to start building that space craft or can I wait a couple weeks, after all a trillion years is just around the corner when talking galactic time.

I love it when Moi is confused.

Oh and nice report thanks, I enjoyed the read.

River

[BossTamsin (imported)]

It's 'dark' in that current theories show that whatever it is, it doesn't really interact with the stuff we're made of, other than gravitationally.

It's a sad state in some ways. First we weren't the centre of the universe, our sun was. Then our sun was just one in an astronomical number in our galaxy, and in an unfashionable end of an arm, too. From there, our place was reduced still further, as just one minor galaxy in our Local Group, which is a small part of the Virgo Supercluster.

If all that isn't enough to make a person feel inconsequential, now it turns out that everything we see around us isn't even made of the same stuff as the vast majority of matter and energy in the universe.

[Slammr (imported)]

Thank You

I will re read it a few times.

Gravitational lens makes sense, so why is it dark matter and not undiscovered matter?

Moi

The mass that astronomers infer for galaxies including our own is roughly ten times larger than the mass that can be associated with stars, gas, and dust in a Galaxy. This mass discrepancy had been confirmed by observations of gravitational lensing, the bending of light predicted by Einstein's theory of general relativity.

Brown dwarf stars and super massive black holes may make up part of the "dark matter," dark meaning we can't see it. It could also be new forms of matter, Weakly Interacting Massive Particles, that don't react with other matter so that we can detect them with instruments. At this point, no one knows what dark matter is. We only see the gravitational effects of it.

[Slammr (imported)]

Is it time to start building that space craft or can I wait a couple weeks, after all a trillion years is just around the corner when talking galactic time.

I love it when Moi is confused.

Oh and nice report thanks, I enjoyed the read.

River

It's only fair play, isn't it? After all, Moi has us confused most of the time trying to figure out what he's saying.