Welcome

Physics Project(Under the guidance of Prof. Atanu Dutta)

Group members• Pallavit Bisht• Tejas Deepak Kadkade• Keshav Matolia• Shouvik Changkakoti

INTRODUCTION

Dark energy is probably the most mysterious idea in all of physics right now. It’s a good deal more mysterious than dark matter, a substance which is itself hidden in the shadows. Dark matter, we can at least map, and understand it as physically distributed in the universe, much like regular matter. But dark energy is so poorly understood that the term is barely even defined.

What is dark energy? Dark

energy is anything that makes certain enormous flaws in modern cosmology

make sense.

After Einstein, physicists had been fairly sure how the universe was evolving: the Big Bang threw all the matter outward, as an explosion does, and now gravity is slowing that outward expansion through the natural tendency of matter to not want to move away from other matter. Einstein said that the universe was static, but later accepted evidence produced by Edwin Hubble that the universe was in fact expanding, and calling the static universe hypothesis his “greatest blunder”.

Yet, surely, even an expanding universe must still make some sense. It was unclear whether the universe would ever fully stop expanding, or perhaps begin to contract back in on itself resulting an eventual Big Crunch. Still, one thing was for sure: the universe sure wasn’t getting bigger faster.

Except it is. Studies looking at Type Ia supernovae, so-called “standard candles” in astronomy, provided the first ever evidence that the expansion of the universe is not occurring more and more slowly, but more and more quickly as time goes on. Arriving in 1998, this was one of the biggest scientific announcements of the century.

Later, evidence from things like maps of the Cosmic Microwave Background radiation showed that this was correct: in defiance of the gravitational influence of matter, the universe is expanding ever faster.

More than that, it seemed that there was simply more stuff in the universe than had been known. The previously mentioned CMB maps can provide a value called the critical density, which given certain observations ought to equal the total amount of matter and energy in the universe. The actual observable amount doesn’t remotely equal this figure, however, and even with dark matter taken into account the universe still only seems to have about a third as much stuff in it as expected.

What is Dark Energy?

In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate.

One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood. The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein's gravity theory, the version that contains a cosmological constant, makes a second prediction: "empty space" can possess its own energy.

A new telescope camera in Chile focused on mysterious

dark energy has taken its first photos of extremely distant

galaxies.

The Dark Energy Camera is designed to study this puzzle by mapping out the distant

universe to more accurate pin down its current and past

expansion rates.

The Dark Energy

Camera

"The Dark Energy Survey will help us understand why the expansion of the universe is accelerating, rather than slowing due to gravity,"

The new instrument — a 570-megapixel camera — took its first photos on Sept. 12, taking aim at a portion of the southern sky from atop a mountain in the Chilean Andes. The Dark Energy Camera was built at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Ill., and was installed on the Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory, the southern branch of the U.S. National Optical Astronomy Observatory (NOAO).

Each photo by the camera can capture up to 100,000 galaxies as far away as 8 billion light-years.

This zoomed-in image from the Dark Energy Camera of the center of the globular star cluster 47 Tucanae, which

lies about 17,000 light years from Earth.

This photo from the new Dark Energy Camera, taken in September 2012, shows the barred spiral galaxy NGC 1365, in the Fornax cluster of galaxies, which lies about 60 million light years from Earth.

Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe

This image shows the distribution of dark matter, galaxies, and hot gas in the core of the merging galaxy cluster Abell 520. The result could present a challenge to basic theories of dark matter.

Another explanation for how space acquires energy comes from the quantum theory of

matter

In this theory, "empty space" is actually full of temporary ("virtual") particles that continually form and then disappear. But when physicists tried to calculate how much energy this would give empty space, the answer came out wrong - wrong by a lot. The number came out 10120 times too big. That's a 1 with 120 zeros after it.

It's hard to get an answer that bad

Another explanation for dark energy is that it is a new kind of dynamical energy fluid or field, something that fills all of space but something whose effect on the expansion of the Universe is the opposite of that of matter and normal energy. Some theorists have named this "quintessence," after the fifth element of the Greek philosophers. But, if quintessence is the answer, we still don't know what it is like, what it interacts with, or why it exists. So the mystery continues.

To outfit the roughly 40-year-old Blanco telescope for the survey, scientists mounted a new instrument called the Dark Energy Camera on top of it in 2012. The camera is designed to image about 200 million galaxies as well as thousands of new supernovae over the course of the survey.

Here scientists build a prototype of the Dark Energy Camera. The camera's wide field of view allows it to regularly scan about one eighth of the sky as well as to look deep at a few select patches of the heavens.

Proving the unseenIf scientists can't see dark matter, how

do they know it exists?Scientists calculate the mass of large objects in space by studying their motion. Astronomers examining spiral galaxies in the 1950s expected to see material in the centre moving faster than on the outer edges. Instead, they found the stars in both locations travelled at the same velocity, indicating the galaxies contained more mass than could be seen. Studies of the gas within elliptical galaxies also indicated a need for more mass than found in visible objects. Clusters of galaxies would fly apart if the only mass they contained were visible to conventional astronomical measurements.

We are thankful to our physics professorProf. Atanu Dutta

To give us this valuable opportunityTo get more knowledge about Dark Energy

We all group members are thankful to you sir..

THANK YOU