Day 8: Relativity & Cosmology

Key moments in history: Albert Einstein introduced his theory of special relativity as the structure of space time. It was introduced in his groundbreaking paper published in 1905 paper "On the Electrodynamics of Moving Bodies"

Key Concepts:

What is Cosmology:

Cosmology is concerned with developing theoretical models about the formation, age and evolution of the universe and its contents, based on observational evidence collected through astronomy and other sciences—notably particle physics.

What is the big bang theory?

It is only one of the most important theories in astronomy. The basics of the theory are fairly simple. All of the current and past matter in the universe came into existence at the same time. At a point in time, about 13.7 billion years ago all matter was compacted into a very small ball with infinite density, and intense heat called a singularity. Suddenly, that singularity began to expand and the universe came into being. That is the basic idea of the big bang theory, read on for further details that will help it become a little more transparent.

First, what a singularity is? According to widely accepted theory, singularities are zones which defy the current understanding that we have of physics. They are believed to be at the core of most black holes. A black hole is an area of intense gravitational pressure. That pressure is theorized to be so intense that finite matter is actually compressed until it has infinite density. This area of infinite density is called a singularity. Our universe is thought to have begun as one of these infinitesimally small, infinitely hot, infinitely dense singularities. The where and why of it all we still don’t have a firm grasp of, but the big bang is the point at which that singularity suddenly began to expand and created our universe as it moved outwards.

Some scientists believed that if our universe was created by a singularity, there would have to be a background heat still in existence in the universe. To understand why a scientist would think there is still heat from the big bang you have to know that the universe is still expanding. Galaxies appear to be moving away from us at speeds proportional to their distance. This is called Hubble’s Law, named after the man who discovered this fact, Edwin Hubble, in 1929. This observation supports the expansion of the universe and suggests that the universe was once compacted. So, if the universe was initially compact and very hot, you would be abler to find some of that heat still. In 1965 two radioastronomers, Arno Penzias and Robert Wilson, discovered a 2.725 degree Kelvin (-454.765 degree Fahrenheit, -270.425 degree Celsius) Cosmic Microwave Background radiation (CMB) which pervades the observable universe. This is thought to be the remnant that scientists were looking for. Another question that comes to mind is whether or not space and time existed prior to the big bang. A trio of highly respected astrophysicists have published papers plainly saying no. Steven Hawking, George Ellis, and Roger Penrose based their work on the basics of Einstein’s theory of general relativity. Their calculations led them to believe that time and space had a definite beginning and the beginning corresponds directly with the big bang. In other words, the big bang was the beginning of everything. The big bang theory is not the only model that tries to explain the origins of our universe. There are several other theories, but the big bang is the most popular and well known. Here is a link the the NASA page about the big bang theory.

What is the universe made of?

In its early stages, the universe was pretty much pure energy and only later did any kind of matter begin to appear as a result of the universe cooling as it expanded. Some cosmologists loosely refer to matter as 'frozen energy'. So, we need to describe what the universe is made of in terms of both matter and energy:

· 73% Dark energy—we don't know what this is, but there is compelling evidence for its existence based on observations that the universe appears to be expanding at an accelerating rate. The spread-out ‘flatness’ of the universe suggests that there is an awful lot of this expansive energy to account for.

· 23% Dark matter—we don't know what this is either, but it needs to be there. There is not nearly enough visible/detectable matter to generate the gravity required to hold galaxies—and clusters of galaxies—together.

· 4% Baryonic matter—we know lots about this, are made of it and spend our lives walking around on it. Indeed any directly observable objects are baryonic matter (all the stars, planets etc). By exclusion this defines something about dark matter, it's not baryonic.

The mystery of the dark Universe

Ordinary matter makes up everything we can see, smell or touch. This matter – which is made from atoms – also makes up planets and stars.

All objects made of atoms pull on each other according to how much matter they contain. This is why a small, low mass object such as an apple falls towards a much more massive object - the Earth.

Astronomers believe that there must also be another kind of invisible "dark matter" which is spread throughout the Universe. By studying the Milky Way and many distant galaxies, they have found that visible matter alone cannot account for their rotation, size and shape. On its own, normal matter would not be able to create enough gravity to hold the galaxies together.

Scientists can also tell that there is some unknown material in the space between the stars, because its gravitational pull influences the path of starlight travelling towards Earth. Dark matter can even act like a magnifying glass, bending and distorting light from galaxies and clusters behind it. Astronomers can use this effect, called gravitational lensing, to map the distribution of dark matter.

Only about 15% of the matter in the Universe is made of atoms. The remainder is dark matter. However, no one knows what dark matter is made of. We do know that it does not absorb, emit or reflect light, because none of our scientific instruments can directly detect it.

Many scientists believe that most dark matter is some unknown subatomic (smaller than an atom) particle that interacts only very weakly with normal matter. If this is true, billions of these particles will have passed through your body by the time you finish reading this article. Experiments buried deep underground may one day capture a few of these particles, finally solving the mystery of what dark matter really is.

How old is the universe and how did it start? It’s about 13.7 billion years old. Needless to say, how it started is a long story and the details are still being figured out.

How big is the universe? The observable universe is about 93 billion light years in diameter. It is quite likely that the universe is much bigger, but any regions beyond 93 billion light years are not only undetectable, but ‘unknowable’ by current scientific theory.

How do we know all this?

Edwin Hubble used the state-of the-art telescopes of his day to firstly show lots of fuzzy patches were indisputably other galaxies and went on to show that the more distant a galaxy was, the more red-shifted it was. This is a clear indication that we live in expanding universe. The more distant a galaxy is, the more space there is between you and it—all of which is undergoing expansion. Thus the spectrum of light from a distant galaxy is much more stretched (i.e. red-shifted), than light from a close one.

Albert Einstein, a little before Hubble, developed a mathematical model of the universe from his work on general relativity. One obvious problem was how to explain why the universe didn’t just collapse in on itself due to the gravitational attraction of the matter within it. He introduced the cosmological constant to account for this—essentially a mysterious expansive force to counteract gravity. Upon hearing of Hubble’s work, he had a Doh! moment, but history has looked well on him as the first person to suggest that there needed to be an expansive force in the universe—that stuff we now call dark energy (because we still don’t know what it is).

Any astronomical observation is a look into the earlier life of the universe. Looking around we find the universe looks pretty much the same in every direction, in terms of matter distribution and space-time. This isotropy gives some validity to the Big Bang model which poses that the universe and everything in it expanded from a single point in all directions in a fairly even fashion.

The Cosmic Microwave Background (CMB) is the earliest observation possible. Originally the first burst of tremendously hot, powerful radiation from the broiling plasma of the primeval universe, it is now so vastly red-shifted that it has a temperature of only 2.7 Kelvin and can only be observed by radio astronomy. The CMB is also very isotropic, but at a fine level of detail it is anisotropic (i.e. there are lumps and bumps) which gives us much useful data about the early universe. The Wilkinson Microwave Anisotropy Probe (WMAP) has been the source of much of this data in recent years.

The CMB is a baby photo of the universe when it was about 380,000 years old. Understanding what happened before that is an exercise in building mathematical models of the increasing temperature and energy densities required as the universe is packed into an increasingly smaller volume. This is where particle accelerators, like the Large Hadron Collider, come in, providing data about what happens to particles in the high energies and temperatures of the early universe. What we find is that familiar atomic particles break down into more fundamental particles like quarks and gluons as the strong, weak and electromagnetic forces are progressively overcome. This takes us from the first three minutes (the title of a good book) down to a fraction of the first second.

Determining what happened at the absolute beginning is still the stuff of complex theoretical modelling based on scanty data. Current thinking involves a quantum fluctuation, a de-unification of the four forces and a bit of symmetry breaking thrown in.

Question of the Day: What is the Big Bang?

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Lesson of the Day:

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Words to Run By:

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Daily Dispatch:

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Video of the Day:

Photos of the Day:

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Expert Video:

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Map of the Day:

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Youth Ambassador Activity:

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School Activity: - Cosmic Colours Exercise

Links: - Atacama ACT Cosmology telescope