Gravitational Lensed “Cosmic Mirage” Is Definitive Proof of Accelerated Expansion of Universe

The Universe is accelerating, says a team of researchers led by Masamune Oguri, Kavli IPMU and Naohisa Inada at Nara National College of Technology, courtesy the data acquired by observing distant quasars. This is supplementary to the studies of distant supernovae, which also showed that the Universe’s expansion is accelerating, and for which the 2011 Nobel Prize in Physics was given. This study with quasars again shows that dark energy is definitely present, but we still don’t know what it might be.

Larger Data and more inferences

The data is derived from the Sloan Digital Sky Survey (SDSS), the huge collaborative experiment responsible for tracking about 100,000 quasars for nearly 10 years, with nearly 50 new quasars discovered in the last few years. Quasars are bright objects, believed to be formed, or at least fuelled, by the accretion of gas and dust by a supermassive black hole. The infalling material glows due to the enormous heat produced and can thus be detected from very far away. This makes them ideal for mapping the gravitational lensing occurring in the Universe.

Prof. Oguri, heading the study, says:

In 2011, the Nobel Prize in Physics was awarded to the discovery of the accelerated expansion of the universe using observations of distant supernovae. A caution is that this method using supernovae is built on several assumptions… Our new result using gravitational lensing not only provides additional strong evidence for the accelerated cosmic expansion, but also is useful for accurate measurements of the expansion speed, which is essential for investigating the nature of dark energy.

The Science of Gravitational Lensing

Gravitational lensing refers to the bending of light due to the presence of matter in the path of light, as explained by Einstein’s General Theory of Relativity. This process creates (at least) two identical images of one object, separated by a gap, thus the name ‘Cosmic Mirage’, referring to the similar process by which mirages on Earth are created.

The formation of a Cosmic Mirage. The figure explains why the accelerated expansion increases the chances of gravitational lensing and why the images separate out further. (Courtesy: SDSS)

The farther away the quasar, the greater its chances to be gravitationally lensed. Accelerated expansion of the Universe increases the distance of the quasar from us and thus the images also seem to separate (refer to figure above). This can be used to deduce how fast the quasars are receding from us. By plotting the velocity graph (velocity versus distance curve), we can see the deviation from the straight line expected from Hubble’s law, if the Universe was expanding at a constant rate. Sure enough, there is deviation and all the deviations fall on a curve, showing that it’s not just a mere statistical fluctuation or measurement error. The Universe is indeed accelerating! And this suggests that the estimates for dark energy are also not very off.

Note the two distinct images formed by gravitational lensing in the zoomed in inset. This was captured by the Hubble Space Telescope and the quasar - SDSSJ1226-0006 - has been tracked by the SDSS. (Courtesy: SDSS and Hubble Space Telescope)

Dark Energy in Einstein’s Theory

Einstein’s theory of General Relativity allows for an expanding Universe without any extraneous assumptions. However, this expansion should have been at uniform speed. But it seems that the expansion rate is increasing. To get this prediction from Einstein’s equations, scientists tweak it a bit, adding a ‘cosmological constant’ term. This adds a bit of energy per unit volume of the Universe, contributing a lot to the entire energy of the Universe. By adjusting the sign of this extra term, the universe can be made to be accelerating.

In fact, it can be shown that we are exiting a phase dominated by matter, where the major contribution to energy comes from matter, and entering a phase dominated by the cosmological constant. This inevitably leads to accelerated expansion. We might not be able to see any galaxies in another 5-10 billion years, if the accelerated expansion of the Universe continues unabated.

The SDSS data also shows that treating dark energy as the cosmological constant is not such a wrong thing to do.

The future of the SDSS project is Planck and the SuMIRe projects. Both aim to study the distribution of cosmic dark energy and all this in the not-too-distant exciting future!

Source and more info at the IPMU original site: http://www.ipmu.jp/node/1281

Now, Light Can Travel Faster Than The Speed of Light!

Now light would lose to light, if it were to race against itself. Researchers have now made light propagate through special media at speeds faster than the conventional speed of light (a mind-boggling 299,792,458 m/s). However, Einstein and his many fans need not worry; this faster-than-light propagation doesn’t violate relativity, which states that the speed of light is the fastest speed possible.

Building Packets of Waves

The secret to such a feat is the building up of wave-packets. Wave-packets are exactly what their name suggests packets of waves. Interference of waves is the key phenomenon.

Waves have the unique property to interfere, whether it be constructively or destructively. When two waves overlap, peak to peak, the overlap or interference is maximal. This is called constructive interference. When the waves overlap, such that peak and trough coincide, they cancel each other’s contribution out, giving destructive interference.

Interference pattern formed by the interference of light from two sources. Notice the dark ridges, where light interferes destructively. The bright regions is due to constructive interference

By selecting a large number of waves (theoretically, an infinite number), differing from each other by fraction of their wavelengths, a wave-packet can be built, such that it has a central peak, smoothly falling off on either sides. The waves interfere constructively near the peak and destructively further away from it. Thus, we arrive at an important conclusion: The constituent waves determine the position and magnitude of the peak of the wave-packet, through their mutual interference.

Wave Packet formation.

If we could find a material, which would selectively allow only certain wavelengths to go through, a wave-packet can be suddenly deformed when it enters a medium. Also, we could shift the location of the peak.

Shifting peaks and moving fast

Enter Vitaliy Lomakin of the University of California, San Diego and his colleagues at the Public University of Navarre in Pamplona, Spain. They used Teflon as the propagating medium. Microwave radiation was made to pass through a copper disc sandwiched between two Teflon discs. It was noticed that the wave jumps forward, emerging from the back Teflon plate, before it enters the metal plate. The team reported sending 10% of the light 10 picoseconds earlier than usual.

Einstein still stands tall

Physicists interpret the postulate of relativity to mean that information cannot be transferred faster than light. Here, no useful information can be transferred for that the entire wave-packet has to be transferred, not some part of it. The wave-packet is highly distorted, and also markedly reduced. Causality is not violated.

Einstein still stands, even though light can now travel faster than itself. The findings will soon be published in the prestigious Physical Review Letters.

CERN’s New Einstein Observatory To Detect Gravitational Waves

CERN’s at it again, but it’s not particle physics. Einstein’s also at it again, but this time, it isn’t the famed grizzly haired scientist. A group of European scientists working with CERN will soon propose a design for a telescope the Einstein Observatory  – which will be much better than any other known telescope of its kind. The catch: This one will detect gravitational waves rather than optical radiation or radio waves.

What is the Einstein Observatory

The Einstein Observatory (EO) is a ‘third-generation’ gravitational wave detector and it is designed to be at least a 100 times more sensitive that its existing predecessors. The principle of detection is simple and classic. The arms of the Observatory, each several kilometers long and each being a laser beam will shrink or expand ever so slightly if a gravitational wave passes. This will cause a change in the interference pattern in a central photo-detector. Let’s look at this in more detail.

Einstein’s theory of General Relativity predicts that gravitational energy, stored in gravitational fields, should be released as waves, just like energy in electromagnetic fields is released by electromagnetic waves (which we call light). The problem is that, unlike light, the energy of a gravitational wave is so small that if a typical one passes by earth right now, the earth will shrink and then expand by the breadth of a proton which is much much smaller than even an atom. Detecting such small perturbations is a huge challenge that has so far been unconquered. Relativity predicts that gravitational waves of comparatively large magnitude are emitted by violent cosmic events, like merging of black holes, or fusing of neutron stars, or even supernova explosions. These will be the typical gravitational waves scientists hope to detect with EO. The success of Einstein’s theory has been such that no one doubts the existence of gravitational waves, even though one hasn’t been detected inspite of dedicated search.

Gravity waves are generated by violent cosmic event, like neutron stars merging (An artist's impression)

What EO intends to do is this: there is a particular way two beams of light interfere with each other.

Apparatus for the MM experiment

They form a well-known pattern called an interference pattern (you might see these patterns when water waves interfere). A slight shift in the path a beam of light travels will disturb these patterns. The process is extremely sensitive – and if the beams travel a long distance before interfering, the sensitivity increases. (For science buffs: This is the same principle first used by Michelson in his famous experiment for measuring the speed of light and later, the most famous ‘failed’ experiment in history. This failed experiment, known simply as Michelson-Morley experiment, aimed to detect a change in the speed of light in different directions so as to confirm the aether hypothesis. None was detected. Einstein would later build his Special Theory of Relativity around this result.)

More on the EO

The EO will be housed 100 to 200 meters below ground, in order to minimize the seismic activity of the ground and its effect on the telescope. The EO will be extremely sensitive in the range 1 Hz to 10 kHz, which is the frequency band for the gravitational waves. The Einstein Observatory will lead a scientific revolution, is what Michele Punturo, scientific coordinator of the design, says. The data from the EO will be corroborated and complemented by data from various gamma-ray and X-ray telescopes.

The proposed design of the Einstein Observatory

The EO is actually two interferometers one to detect gravitational wave signals from 2-40 Hz and the other to detect till 10 kHz. This is required, since detecting at low frequencies is a very difficult job and needs dedicated instruments tuned for doing only that.

EO will hope to improve upon existing gravitational wave telescopes like LIGO, Virgo and TAMA (all first generation), and even Advanced LIGO and Advanced Virgo (second generation). The design will be presented at European Gravitational Observatory site in Pisa, Italy.

It is of utmost importance to the progress of cosmology that the telescope, like the illustrious scientist it is named after, becomes as successful as his theories.

Einstein Confirmed Again: Dark Energy Present In The Universe

The grand old man of Physics is proved right once again. Albert Einstein was vindicated yet again by a survey, which confirmed the presence of Dark Energy in the Universe. The ‘WiggleZ Dark Energy Survey’ was conducted by 26 astronomers from 14 countries using the latest in spectrograph technologies to map out more than 200,000 galaxies, many halfway across the Universe to confirm this startling fact.

What is Dark Energy?

Dark Energy is the name given to the unknown entity believed to be behind the acceleration of the expansion of the Universe. It was Edwin Hubble, who in 1932, first noticed that the Universe was actually expanding. This gave a huge boost to the Big Bang theory, which says that the Universe came out of an ultra-dense singularity 14-15 billion years ago. Scientists have been expecting the expansion to slow down as time wears on, as then gravity will eventually dominate. What scientists found, instead, was that the Universe was expanding at an ever-increasing rate. It is believed that some mysterious source of energy was aiding the expansion process, thus named Dark Energy.

No one has come up with a proper explanation of Dark Energy, despite there being a number of hypotheses and models. Dark Energy supposedly makes up 73% of the Universe, Dark Matter 23 % (which is NOT the same as Dark Energy; Dark Matter slows down the expansion) and the rest 4% – is ordinary matter – stars, galaxies, nebulae and super-clusters.

Where Einstein fits in…

Einstein had almost predicted the expansion of the Universe in his Theory of General Relativity, but in an uncharacteristic situation in which his nerves weakened, he introduced a factor in his equations which predicted a static Universe. This amounted to including in his equations, a cosmological constant a ‘fudge factor’ which gives vacuum a repelling force, effectively enabling the Universe to counter its own gravity and preventing self-collapse. Later, Einstein would rue this as his ‘greatest blunder’. Now, it seems that the great man was not wrong!

Inflationary theories of modern cosmology use this idea of a cosmological constant to explain the supposed period of rapid expansion right after the Big Bang called inflation. Now, with the increasing rate of expansion, it seems that the cosmological constant was the genius’ masterstroke rather than a botch-up.

The WiggleZ survey

The WiggleZ survey, conducted by an Australian-based group led by Dr. Michael Drinkwater, used the latest in spectrography, thanks to latest Australian technology to survey galaxies more than 200000 of them some 7 billion light years away. Light takes a finite time to travel from one place to another, because of its finite speed. Thus the light from 7 billion light years away took 7 billion years to reach here. This means that we are seeing galaxies in the form they were 7 billion years ago, essentially looking back in time! (Thus, the easiest way to glance into the past is to just see. The farther away the object you see, the farther away in time it is!). The WiggleZ survey can map 392 galaxies in an hour!

Do Structures such as these give clues to Dark Matter and Energy?

Though, this doesn’t tell us the constituents of Dark Energy (or Dark Matter, which is also a mystery), it gives definitive confirmation of its existence. It gives scientists confidence that Einstein’s theory is not failing, and that Dark Energy can indeed be reconciled with General Relativity. The survey is exhaustive measuring both the pattern of distribution of galaxies in the Universe and the rate of formation of the galaxy clusters, essentially giving scientists a two-way confirmatory proof of Dark Energy.

So, there it is again! Einstein is proved right again, and in spectacular fashion. 96% of the stuff in the Universe is unknown, but at least we know that it’s there. Some consolation and a lot of work to be done!

Einstein Passes Strictest Test: NASA’s Gravity Probe-B Proves General Theory of Relativity Correct

It is the culmination of a five-decade old project. Gravity Probe-B (GP-B) has detected a minuscule, but theoretically expected, tilt in its magnetic needles, essentially proving Einstein correct, yet again.

einstein
"Told ya"

The Physics

Einstein’s general theory of relativity (GTR), the most accurate description of gravity known to science, predicts two critical phenomenon, which differentiates it from Newton’s theory of gravity: geodetic effect and frame dragging. The geodetic effect is just a technical term to describe the well known phenomenon of warping of space-time by massive objects. Light, which appears to follow a straight line path, will bend, following the curvature of space-time. Frame dragging refers to the phenomenon in which space-time seems to be ‘dragged’ along with any rotating gravitational body. It’s as if there is friction between the body and surrounding space-time.

Physicist Francis Everitt, of Stanford University, lead researcher in the GP-B experiment, explains it better:

Picture the Earth immersed in honey, and you can imagine the honey would be dragged around with it. That’s what happens to space-time. Earth actually drags space and time around with it.

francis everitt
Francis Everitt

If Einstein’s theory is really true, then these effects should lead to a tiny, but observable, in the orientation of a suspended gyroscopic magnet.

The Project

The project was proposed by theoretical physicist Leonard Schiff in 1959, when he was the head of the Stanford Physics Department. In 1962, Schiff and team recruited Everitt. In 1963, NASA got interested in the project, a full 7 years before the lunar launch.

The experimental confirmation of such tiny effects was a huge challenge. Einstein, himself was of the opinion that

their magnitude is so small that confirmation of them by lab experiments is not to be thought of.

Thankfully, Einstein was wrong. In 2004 (after 41 years), the Gravity Probe-B was launched by NASA.

The spacecraft had four ping-pong sized gyroscopes. These were made of fused quartz spheres (the most spherical spheres ever made) and uniformly covered by a layer of Niobium and cooled by Liquid Helium. At liquid Helium temperatures, Niobium becomes a superconductor, allowing electrical currents to flow without any resistance. Once an electrical current is setup, it doesn’t decay.

One of the four Gyroscopes on Gravity Probe B
gravity probe b
Gravity Probe B

Rotating currents setup a magnetic field pointing in a particular direction. The magnetic pointer was set to point at IM Pegasi, a single star. The prediction is that, if Einstein is right, minute changes in the direction of the magnetic pointer would occur.

The Result

The pointer shifted by 6000 milli arcseconds in one year that’s the breadth of a human hair seen from 10 km away. However, the extent was just as expected, confirming GTR yet again. The geodetic effect was confirmed to within 0.23% accuracy and the frame-dragging to about 20%.

Beyond just Einstein

Even though the primary objective of this project was to verify GTR in the most accurate way possible, GP-B has also, unwittingly, contributed a lot to the development of various technologies, most notably the technology to build better gyroscopes. It has made key contributions to various developments on the COsmic Background Explorer (or COBE), which was instrumental in demonstrating that the Universe is expanding just as the Big Bang Theory claims.

Consequences

The positive GP-B results will help scientists understand gravity better, especially in extreme cases, like black holes. Many people ask, why test Einstein further? Well, even though he has been thoroughly tested and has passed all tests with flying colors, that’s how science proceeds. The more stringent the test, the more credibility the theory gains when it passes it.