The Dark Energy Survey camera will investigate millions of galaxies for the subtle effects of weak lensing.
Image: R. Hahn/FERMILAB
-
Gravity's Engines
We’ve long understood black holes to be the points at which the universe as we know it comes to an end. Often billions of times more massive than the Sun, they...
Read More »
By Eric Hand of Nature magazine
Even the best pictures of a distant galaxy are a bit lopsided. But this is an attribute, not a bug. Because mass distorts space-time, light coming from distant galaxies is bent as it passes through intervening shoals of invisible matter, leaving the images of these distant objects minutely sheared and stretched.
Two astronomical surveys now scheduled to come online seek to take advantage of this effect, which is known as weak gravitational lensing. The surveys aim to use the technique to get a firmer handle on dark energy, the mysterious force that is apparently speeding up the expansion of the Universe. By observing the patterns of distortions across large swathes of sky (see ‘Falling into line’), astronomers hope to map the density and distribution of dark matter, the web-like invisible scaffolding around which visible matter is thought to have first coalesced. Then, by looking at changes in this hidden web across cosmic time, they hope to discern the imprint of dark energy.
Observers already study the effects of dark energy by tracking cosmic landmarks: the standard candles of distant supernovae and the standard rulers of ripples in the distribution of galaxies. But those techniques reveal only how the Universe’s expansion rate has changed because of dark energy. Weak lensing offers an extra prize: the distortions hold clues to the action of gravity at far-off locales. The technique can thus address an increasingly pressing question for theorists: what if the Universe’s accelerated expansion is not the result of dark energy’s mysterious anti-gravitational force, but is instead a sign that gravity behaves differently in different parts of the Universe?
“It provides unfettered insight into the properties of gravity that we can’t get by other techniques,” says Rachel Bean, an astrophysicist at Cornell University in Ithaca, New York. “Its potential is massive, but so are the challenges.”
Unlike strong gravitational lensing, in which a major concentration of mass markedly distorts the image of a single galaxy, the subtle effects of weak lensing can be detected only in detailed surveys of millions of galaxies. One of the new efforts will use the Hyper Suprime-Cam (HSC), which achieved first light on 28 August on the 8.2-metre Subaru telescope in Hawaii. By 2018, it aims to have imaged 10 million galaxies over a 1,500-square-degree-swathe of the sky, says Satoshi Miyazaki of the National Astronomical Observatory of Japan in Mitaka, who is the principal investigator of the HSC survey.
A rival project, the Dark Energy Survey (DES), is set to start operating later this month on the 4-metre Blanco telescope in Chile, says its principal investigator, Josh Frieman of the Fermi National Accelerator Laboratory in Batavia, Illinois. Being the main project for the Blanco telescope, the DES will get more observing nights than the HSC, allowing it to image 300 million galaxies over 5,000 square degrees by 2018. But its smaller telescope means that it will not be able to peer as deeply into the distant Universe as the HSC survey.
Even with these massive digital cameras — 870 million pixels for the HSC and 570 million pixels for the DES — weak lensing “is a very, very difficult measurement to make”, says Bean. To detect the subtle distortions caused by lensing, for example, astronomers must subtract aberrations caused by the optics of the telescope and by Earth’s atmosphere.
Doing the measurements from space could help. The European Space Agency is planning to launch a dark-energy probe called Euclid in 2019. And in the United States, an as-yet-unfunded dark-energy mission called the Wide-Field Infrared Survey Telescope, which would dedicate much of its time to weak-lensing measurements, was ranked as the top priority for space-based astronomy in a 2010 decadal survey.
See what we're tweeting about
20 Comments
Add CommentVery interesting post! I have never hear about this!
Reply | Report Abuse | Link to thisThe article states that matter distorts space-time and light from remote galaxies propagates the distorted space-time. This will give rise to gravitational lensing effect.
Reply | Report Abuse | Link to thisDoes dark matter and dark energy also distorts space-time which should be reflected in additional gravitational lensing? If dark matter and dark energy exist and they also distorts space-time which should lead to some gravitational lensing over and above caused by luminous matter and energy.
The possibility that dark energy and dark energy might be existing but NOT distorting space-time but only casting gravitational influence can not be ruled out. If this turns out to be a reality despite existence of dark matter and dark energy, no lensing effect may be detected due to distortion, however, effect of extra gravitation may be detectable.
Dark energy was hypothesized in the late nineties of 20th century to account for the accelerated expansion of universe as inferred from the red shift of remote galaxies. In cosmology, expansion of universe is interpreted as expansion of space. Expansion of not even a single inch of space has been measured directly. Increasing red shift of light from red shift is interpreted as increasing distance between observer and light emitting galaxies . This increasing distance between galaxies is interpreted to arise from expansion of space
Reply | Report Abuse | Link to thisIf expanding space between galaxies leads to increased distance between material galaxies, it implies matter of galaxies is hinged with space. If there would have been no such hinging between space and galaxies, distance between galaxies should have remained constant and expanded space slipped beneath galaxies.
Projects to study dark energy are quite costly projects entailing billion of dollars. For the sake of advancement of scientific knowledge, no one should have any reservation for costly projects BUT before launch of such projects, scientists should have complete conceptual clarity on many issues of space and its expansion. Some of such issues are given below :
A Nature of Space
i)What is "that" in space which expands?
ii)From "where" extra space has been emerging on expansion since since BB?
iii) In relativity, which is considered as mainstream theory of Physics, physicality of space has been taken to be NIL. Why a dark energy carrying some physicality should be required to be invoked to cause expansion of space having NIL physicality
iv) Space like matter and energy can not be compartmentalized, therefor, if it has been expanding it should be expanding as a unified whole. It can not expand in sections -- with space at remote distances expanding and within MW galaxy and other nearby galaxies not expanding.
B Nature of Force between matter and space
What is the nature of force between matter of galaxies and space due to which galaxies remains hinged with space so that on expansion of space actual distance between galaxies increases.
I think important conceptual issue is not if space is expanding at accelerating rates or decelerating rates or constant rates, but even more crucial issue is to have clear understanding of aforesaid issues.
Instead of spending billion of dollars on dark energy exploration projects, with entire Globe suffering acutely from from resource crunch, it will in the fitness of things to FIRST fix the unresolved issues of nature of space and expansion
Ai) Space.
Reply | Report Abuse | Link to thisAii) Nowhere. Same place the extra elastic band comes from, when you stretch it.
Aiii) No, it is not. That leaves no content in your question.
Aiv) Yes, it can. It's a matter of scale and time.
Maybe you should read an introductory physics text book FIRST before writing exactly the same comment on every article that happens to mention dark energy on a popular science website that wasn't made to answer questions in philosophical nitpicking over misinterpretations of words. Fixing the unresolved issues of space and expansion is exactly what this research is all about. The real unresolved issues, that is, not the unresolved issues of what you think the words mean.
The language used to discuss this physics problem is clouded by semantics. Words like "stretch" and "expand" and bla bla bla..... make a mockery of the mathematics and other notional languages that provide exquisitely exact descriptions of phenomena. Otherwise, lets use dice and knucklebones to promote discourse that does not rise above the level of primitive metaphor to produce a single cogent THOUGHT.
Reply | Report Abuse | Link to thisYour illustration of extra elastic bond ( may be comprising of some rubber or alike material) does not hold good since in elastic bond we know that it is composed of rubber molecules and on stretching space between molecules increases. Yes, this is exactly the issue not understandable in case of expansion of space. Since we do not know any thing about physicality of space (In fact relativity speaks of NIL physicality) but assert expansion of space.
Reply | Report Abuse | Link to thisMost of the introductory books of Physics and links of wikipedia and other related links on space expansion speak of space expansion in mathematical terms but they are silent on the physical mechanism behind expansion.
Yes, I agree I have been repeating similar comments under different articles on dark energy and expansion since I have not got satisfactory explanation from any source or reader.
When I raise the query of " hinging" of galaxies with space, to enable expanding space to drag galaxies along with it, what is inappropriate in it?
One should not remain oblivious of the fact that mathematical equations per se are not reality but they are only a mode of representation of reality. Without discounting the significance of mathematical treatment, conceptual understanding of physical mechanism behind any phenomenon is of equally, if not, significance
I calculated and found that 10^24 black particle can give birth a photon particle of mass 1.659x10^-54 gram. Both of its has structure, the structure changes means properties changes.A good relation is there between black and photon particle, even graviton particle has mass and structure. Three particles are co-related. This facts written in my book Complete Unified Theory ( pages-424, 1998). So, I able to find the "Master Key of the Universe" and this can explain all facts which are unknown to us till now. ---- Nirmalendu Das
Reply | Report Abuse | Link to thisWhy is it necessary to come up with the convoluted concept of dark energy when the equations for the expansion of the universe are in the fourth section of Einstein's Theory of Relativity?
Reply | Report Abuse | Link to thisIs weak lensing similar to the Gravitational Lensing predicted by Einstein? How can gravity bend light from such distances? Is Dark Matter capable of gravitational lensing and weak lensing just light visible light?
Reply | Report Abuse | Link to thisRichard
richaugelli@gmail.com
Gravitional Lensing is exactly the same. Anything that has mass causes it. Whether it is "weak" or "strong" depends on the object causing it. A massive blackhole can cause strong lensing. Something like a galaxy, being more diffuse, will have a weaker lensing effect.
Reply | Report Abuse | Link to thisthe light bending is not over great distances. Imagine three things roughly in line:
A____________B----------C
A is some very distant galaxy. It's light passes B which is some massive object. B causes the light to bend toward C which is us observing the result. The distances from A to B and B to C are tremendous. In comparison, the light beam approaches closely to B. With the long distances involved, even a small bending may be measurable.
HTH
Note to rja2012 I was referring to the predictions on gravity, gravity waves, and the expansion of the universe caused by gravity waves. Those predictions were made at the Leningrad Institution for which a Nobel Prize was awarded.
Reply | Report Abuse | Link to thisAdditional explanation to rja2012. When a hydrogen bomb explodes, far more energy is given off than is predicted by Einstein's equation e=Mc^2. The additional energy comes from gravity waves from the Gravitational section of the Theory of Relativity. The gravity wave front is repulsive.
Reply | Report Abuse | Link to thisWhen a gravity wave front has gone half way around the universe it turns into gravons which become attractive. The earliest gravity wave fronts have done this and have become gravons and have become gravons in the outer reaches of galaxies.
You will need to read the research from Leningrad University for a better understanding.
First light images from the Dark Energy Camera on the 4m Blanco telescope have recently been posted online:
Reply | Report Abuse | Link to thishttp://www.fnal.gov/pub/presspass/press_releases/2012/DES-DECam-201209-images.html
First light images from the Hyper Suprime-Cam have not, at this time, been released.
The article deals with the endeavour of scientists to establish the existence of dark regime of universe -- dark matter and dark energy thru study of weak gravitational lensing. It was established long ago by Eddington in 1919 that ordinary luminous matter distorts space-time due to which lensing effect is produced. Actually, at that nothing was hypothesized about dark matter and dark energy.
Reply | Report Abuse | Link to thisOf course, dark matter and dark energy cast gravitational influence upon ordinary matter. In fact, dark matter was hypothesized to account for the extra gravitation in universe, as reflected in the motion of stars and galaxies which could not be explained thru only ordinary luminous matter.
The question arises : can dark matter and dark energy also distorts space-time leading to lensing effect. In fact, dark energy was hypothesized to account for accelerating expansion of space and not any distortion in space-time. So how dark energy ( not dark matter) will create distortion in space-time. This aspect is not clarified by article
Gravity waves are hypothesized waves which are created in the "fabric of space-time". But what "fabric of space-time"? What is the physicality of fabric of space-time? If space carries no physicality, how gravity waves generated in such fabric can have any physicality?
Reply | Report Abuse | Link to thisVino, I believe you are on the right track, which means don't expect much acceptance toward your line of questioning by the mainstream. They have vested interest in maintaining current beliefs. Especially the second law of thermodynamics, which is a keystone concept needed worse than a fish needs water for this world to persist.
Reply | Report Abuse | Link to thisThe big bang depends upon proof that the universe is expanding. The universe expanding depends upon proof that a redshift occurs in the light from distant stars. The redshift depends upon proof that photons do not attract each other. This is where the whole house-of-cards falls apart. Photons do in fact attract each other because photons have gravity!
Reply | Report Abuse | Link to thisAs photons travel from distant stars, photons diverge and the light dims. But since photons separate to diverge, they lose energy because of their mutual gravity. This results in the "redshift". So, the universe is not expanding, and the big bang is only an illusion.
Vino, gravity waves are not hypothesized on the fabric of space time. Go back and read both the coulombic and the gravitational sections of The Theory of Relativity and then read the research from The Leningrad Institute. When and electric current is created, direct or alternating, a powerful repulsive force is created. When an electric current is run through an electro magnet, for a thousandth of a second it is repulsive. When the electromagnetic field is established the electromagnet begins attracting iron. When the current is destroyed, it becomes repulsive as it is destroyed. AC current is repulsive. It will not work in an electromagnet but can be used to toss metallic objects from a conveyor belt into the air.
Reply | Report Abuse | Link to thisIn the gravitational section of the theory of relativity gravitational forces replace coulombic forces. The gravitational constant replaces the coulombic constant.
Now, since everything else has worked the same so far concerning gravity as predicted in Einstein's theory, it might make sense to assume that when mass is destroyed, the gravity associated with that mass would also be destroyed. It might make sense to assume that when the gravity associated with that mass is destroyed, Einstein's equations apply to that mass and its associated gravity.
So, gravity waves are not created in the fabric of space time but by an atom losing mass. They have almost no effect at a short distance because their strength is overwhelmed by much larger masses times a weak gravitational constant. However, gravity waves like radio waves go unimpeded into outer space: the gravitational force from the galaxy where they originated drops off as the square of the distance. There comes a point where the gravity waves pushing a group of galaxies away from its neighbors becomes more powerful than the gravitational force trying to bring them together.
(The same theory would have the universe increase some 50 times larger almost instantaneously. Indications exist that happened.)
"gravity waves are not hypothesized on the fabric of space time."
Reply | Report Abuse | Link to this"So, gravity waves are not created in the fabric of space time but by an atom losing mass."
From your above quotes in blog 18, I infer gravitational waves are the product of loosing mass by an accelerating massive object on the same pattern a moving charged body produces e.m waves. In case of e.m waves, it is the loss of charge and in case of gravitation waves it may be the loss of mass. Without any loss of charge or mass, how there can be creation and transfer of energy in form of e.m or gravitation waves? Am I right?
If I am right in the above interpretation, this will imply that gravitational waves have nothing to do with the so called "fabric of space-time" on the same pattern e.m waves can pass thru vacuum without need for any fibre of space. As such, describing gravitational waves as "ripples in fabric of space-time" is a misnomer.
However, GR describes gravitation as curvature of space-time and does not mentions gravitation in terms of any force or energy. As such, gravitation is not any entity in terms of any force or energy but it is a specific state of space-time ( curved state) But creation of gravitational waves amounts to creation and transmission of some energy ( from accelerating mass). So how to compromise this contradiction?
Further, GR expresses gravitation in terms of curvature of space-time and expresses the curvature in terms of abstract mathematical co-ordinate system. In fact, curvature was also determined mathematically and as up to date, no curvature has been measured directly. GR does not speaks of any physical mechanism behind curvature of space. In fact, GR is dependent upon continuous and smooth nature of space.
However, I pose a direct and straightforward issue to you. Is there meaning of any phenomenon which could be expressed in mathematical system without any physical reality behind mathematical equations. If curvature of space is a physical realty, it implies there should be some physical realty of space also. This implies space should be comprising of some fabric having some building blocks -- some graininess, some atoms may be of even smaller than Plank scale. If space is comprised of some building blocks, continuous and smooth nature of space shall vanish. This will endanger the very basis of relativity. Again some inconsistency? How to compromise this apparent contradiction.
I am not asking you to neceassrly address the above issues but please admit that these are unresolved issues
You are completely right, Vino
Reply | Report Abuse | Link to thisThe 'fabric' idea is what screws it up. It's a bias and they don't see it.
In medieval times they used the Rack to stretch people on. This worked because the rack remained stationary while the person was lengthened along it. Essentially the rack remained the same size while the person expanded in length. They currently measure the expansion of the universe against a rack. This is not an element of GR though. It's a metric measurement system introduced by Minkowski.
There's no rack though. The expansion of the Universe is fractal. Going back in time, the galaxies may appear to get closer, but they never actually meet. No Big Bang, sorry.
It comes down to misunderstandings about length and time, which comes down to not understanding time. We don't understand time, and yet time is the essential element on which rely thermodynamic laws. Those are the laws that make energy the most important commodity on the planet. They who have the most money can direct where research does and doesn't go. Disprove the 2nd Law? There's no funding for such heresy. Dream up some way to keep the Minkowski metric? Here's a Nobel for you.