Dark energy DOES exist and it's increasingly driving our universe apart, scientists claim
Scientists measured the separations between pairs of galaxies and observed that dark energy (represented by purple grid) is a smooth, uniform force that dominates over the effects of gravity (green grid)
Two ways of measuring how fast the universe is expanding. In the past, distant exploded stars have been used as 'standard candles' to measure distances in the universe, and to determine that its expansion is actually speeding up. They glow with the same instrinsic brightness, so by measuring how bright they appear on the sky, astronomers can tell how far away they are. This is similar to a standard candle appearing fainter at greater distances. [second method - sound waves from the very early universe left imprints in the patterns of galaxies, causing pairs of galaxies to be separated by approximately 500 million light-years -- this 'standard ruler' was used to determine the distance from the galaxy pairs to Earth]
By Daily Mail Reporter Last updated at 6:14 PM on 20th May 2011
Dark energy is driving our universe apart at accelerating speeds, according to a five-year survey of 200,000 galaxies, stretching back seven billion years in cosmic time.
The study offers new support for the favoured theory of how dark energy works - as a constant force, uniformly affecting the universe and propelling its runaway expansion.
Its findings are based on results from Nasa's space-based Galaxy Evolution Explorer and the Anglo-Australian Telescope on Siding Spring Mountain in Australia.
But they contradict an alternate theory, where gravity, not dark energy, is the force pushing space apart.
According to this alternate theory, with which the new survey results are not consistent, Albert Einstein's concept of gravity is wrong, and gravity becomes repulsive instead of attractive when acting at great distances.
'The action of dark energy is as if you threw a ball up in the air, and it kept speeding upward into the sky faster and faster,' said Chris Blake of the Swinburne University of Technology in Melbourne.
Blake is lead author of two papers describing the results that appeared in recent issues of the Monthly Notices of the Royal Astronomical Society.
'The results tell us that dark energy is a cosmological constant, as Einstein proposed. If gravity were the culprit, then we wouldn't be seeing these constant effects of dark energy throughout time.'
Dark energy is thought to dominate our universe, making up about 74 per cent of it. Dark matter, a slightly less mysterious substance, accounts for 22 per cent. So-called normal matter, anything with atoms, or the stuff that makes up living creatures, planets and stars, is only approximately 4 per cent of the cosmos.
The idea of dark energy was proposed during the previous decade, based on studies of distant exploding stars called supernovae. Supernovae emit constant, measurable light, making them so-called 'standard candles', which allows calculation of their distance from Earth.
Observations revealed dark energy was flinging the objects out at accelerating speeds.
The new survey provides two separate methods for independently checking these results. This is the first time astronomers performed these checks across the whole cosmic timespan dominated by dark energy.
Astronomers began by assembling the largest three-dimensional map of galaxies in the distant universe, spotted by the Galaxy Evolution Explorer.
'The Galaxy Evolution Explorer helped identify bright, young galaxies, which are ideal for this type of study,' said Christopher Martin, principal investigator for the mission at the California Institute of Technology in Pasadena. 'It provided the scaffolding for this enormous 3-D map.'
The team acquired detailed information about the light for each galaxy using the Anglo-Australian Telescope and studied the pattern of distance between them.
Sound waves from the very early universe left imprints in the patterns of galaxies, causing pairs of galaxies to be separated by approximately 500 million light-years.
Blake and his colleagues used this 'standard ruler' to determine the distance from the galaxy pairs to Earth.
As with the supernovae studies, this distance data was combined with information about the speeds the pairs are moving away from us, revealing, yet again, the fabric of space is stretching apart faster and faster.
The team also used the galaxy map to study how clusters of galaxies grow over time like cities, eventually containing many thousands of galaxies.
The clusters attract new galaxies through gravity, but dark energy tugs the clusters apart. It slows down the process, allowing scientists to measure dark energy's repulsive force.
'Observations by astronomers over the last 15 years have produced one of the most startling discoveries in physical science; the expansion of the universe, triggered by the big bang, is speeding up,' said Nasa's Jon Morse.
'Using entirely independent methods, data from the Galaxy Evolution Explorer have helped increase our confidence in the existence of dark energy.'
Tevatron particles shed light on antimatter mystery
No antimatter here (Image: Peter Ginter/Science Faction/Corbis)
06 July 2011 by Valerie Jamieson Magazine issue 2820
WHY the universe is filled with matter rather than antimatter is one of the great mysteries in physics. Now we are a step closer to understanding it, thanks to an experiment which creates more matter than antimatter, just like the early universe did.
Our best understanding of the building blocks of matter and the forces that glue them together is called the standard model of particle physics. But this does a poor job of explaining why matter triumphed over antimatter in the moments after the big bang.
The standard model has it that matter and antimatter were created in equal amounts in the early universe. But if that was the case they should have annihilated in a blaze of radiation, leaving nothing from which to make the stars and galaxies. Clearly that didn't happen.
A quirk in the laws of physics, known as CP violation, favours matter and leaves the universe lopsided. The standard model allows for a small amount of CP violation but not nearly enough to explain how matter came to dominate. "It fails by a factor of 10 billion," says Ulrich Nierste, a physicist at the Karlsruhe Institute of Technology in Germany.
Now researchers at DZero, an experiment at the Tevatron particle accelerator at Fermilab in Batavia, Illinois, have found the largest source of CP violation yet discovered. It comes courtesy of particles known as Bs mesons (arxiv.org/abs/1106.6308).
These are unusual particles because they can transform into their own antiparticle and back again, says Guennadi Borissov, a member of the DZero team based at Lancaster University, UK. That makes them perfect for studying CP violation.
Last year, the DZero experiment studied collisions between protons and antiprotons that create Bs mesons, which then decay into muons. Sure enough, the team found more muons than antimuons, signalling that more matter is created than antimatter.
However, particle physics is littered with findings that disappear as more data is collected. Now Borissov and his colleagues have repeated the study using data from 50 per cent more collisions and the new result boosts the original conclusion (Physical Review Letters, DOI: 10.1103/PhysRevLett.105.081801). "The most likely interpretation is an anomalously high CP violation," says Guy Wilkinson at the University of Oxford.
Admittedly more work is needed to explain why the universe is filled with matter. "This result won't explain all of the matter-antimatter asymmetry," says Val Gibson at the University of Cambridge, "but it could indicate new physics."
Several ideas of what this new physics might be are on the table, including so-called supersymmetric particles. So far, the world's most powerful accelerator, the Large Hadron Collider at CERN near Geneva, Switzerland, has failed to find signs of supersymmetry and this is starting to worry some theorists. But the finding from DZero may turn out to be the pointer they are looking for. "Supersymmetry can easily explain this measurement," says Nierste.
DZero may not be able to say much more about the lopsided universe, though. The Tevatron is due to shut down in September and DZero has now analysed the majority of its Bs meson data. However, an experiment at the LHC, called LHCb, is ideally suited to studying the Bs meson and particles like it. "LHCb has already taken enough data to be competitive with Fermilab," says Gibson, who works on the experiment. Her team hopes to report its own results at a conference in Mumbai, India, in August.
If you have time:Time Might Not Exist, According to Physicists
August 2009 - "History of the Universe .. ya know .. BIG BANG .. more than 10000 years ago .. seriously it was .. no conspiracy .. In the beginning, the Earth was flat. At least it appeared so to its first observers, hunters and gatherers, "
TOPICS: Popular Quantum Physics The Conversation Time
By Sam Baron, Australian Catholic University April 19, 2022
Does time exist? The answer to this question may seem obvious: of course it does! Just look at a calendar or a clock.
But developments in physics suggest the non-existence of time is an open possibility, and one that we should take seriously.
How can that be, and what would it mean? It’ll take a little while to explain, but don’t worry: even if time doesn’t exist, our lives will go on as usual.
A crisis in physics
Physics is in crisis. For the past century or so, we have explained the universe with two wildly successful physical theories: general relativity and quantum mechanics.
Both theories work extremely well in their own right, but the two are thought to conflict with one another. Though the exact nature of the conflict is controversial, scientists generally agree both theories need to be replaced with a new, more general theory.
Physicists want to produce a theory of “quantum gravity” that replaces general relativity and quantum mechanics, while capturing the extraordinary success of both. Such a theory would explain how gravity’s big picture works at the miniature scale of particles.
Time in quantum gravity
It turns out that producing a theory of quantum gravity is extraordinarily difficult.
One attempt to overcome the conflict between the two theories is string theory .. https://theconversation.com/explainer-string-theory-2983 . String theory replaces particles with strings vibrating in as many as 11 dimensions.
However, string theory faces a further difficulty. String theories provide a range of models that describe a universe broadly like our own, and they don’t really make any clear predictions that can be tested by experiments to figure out which model is the right one.
In the 1980s and 1990s, many physicists became dissatisfied with string theory and came up with a range of new mathematical approaches to quantum gravity.
One of the remarkable aspects of loop quantum gravity is that it appears to eliminate time entirely.
Loop quantum gravity is not alone in abolishing time: a number of other approaches also seem to remove time as a fundamental aspect of reality.
Emergent time
So we know we need a new physical theory to explain the universe, and that this theory might not feature time.
Suppose such a theory turns out to be correct. Would it follow that time does not exist?
It’s complicated, and it depends what we mean by exist.
Theories of physics don’t include any tables, chairs, or people, and yet we still accept that tables, chairs, and people exist.
If time isn’t a fundamental property of the universe, it may still ‘emerge’ from something more basic.
Why? Because we assume that such things exist at a higher level than the level described by physics.
We say that tables, for example, “emerge” from an underlying physics of particles whizzing around the universe.
But while we have a pretty good sense of how a table might be made out of fundamental particles, we have no idea how time might be “made out of” something more fundamental.
Saying that time does not exist at any level is like saying that there are no tables at all.
Trying to get by in a world without tables might be tough, but managing in a world without time seems positively disastrous.
Our entire lives are built around time. We plan for the future, in light of what we know about the past. We hold people morally accountable for their past actions, with an eye to reprimanding them later on.
We believe ourselves to be agents (entities that can do things) in part because we can plan to act in a way that will bring about changes in the future.
But what’s the point of acting to bring about a change in the future when, in a very real sense, there is no future to act for?
What’s the point of punishing someone for a past action, when there is no past and so, apparently, no such action?
The discovery that time does not exist would seem to bring the entire world to a grinding halt. We would have no reason to get out of bed.
Business as usual
There is a way out of the mess.
While physics might eliminate time, it seems to leave causation intact: the sense in which one thing can bring about another.
Perhaps what physics is telling us, then, is that causation and not time is the basic feature of our universe.
If that’s right, then agency can still survive. For it is possible to reconstruct a sense of agency entirely in causal terms.
At least, that’s what Kristie Miller, Jonathan Tallant and I argue in our new book.
We suggest the discovery that time does not exist may have no direct impact on our lives, even while it propels physics into a new era.
Written by Sam Baron, Associate professor, Australian Catholic University.
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