THE BIG BANG THEORY

BY: ANA CABELLOS,NURIA JEREZ & LUCIA SAN JUAN4ºESO B

History of the big bang

-Dicoveries in astronomy and physics have shown that universe started in a proccess called The Big Bang.

-This theory tries to explain what happened.

-Thanks to all the observations we say the universe started 13.810 million years ago.

-Since then the universe has suffered 3 different phases.

-The future of the universe is not clear.

History -The Big Bang occurred in an infinitely dense and hot spot. It wasn’t a normal explosion as the ones we know.-Immediately after the moment of the "explosion" every particle of matter began to move away very quickly, so it started occupying more space and that’s why expanded so much.

History

-This theory indicates that in the past these elements were closer than today, so if we go back in time, then all the stuff was together at one point. That point is called singularity, which was a fireball.

Development

-Einsten: he came up with 10 field equations to support his theory of relativity.

-Friedmann: proposed a close universe, where everything would finish as it started in one point, and an open universe, where the universe would continue expanding for ever, with no end.

-Hubble: measured the distance to the nearest nebulae and showed that these systems were indeed other galaxies.

-Slipher: discovered that almost all such nebulae were receding from the Earth.

Problems

Between the 1920s and 1930s almost every cosmologist preferred an eternal steady state of the Universe and several complained that the beginning of time implied by the Big Bang imported religious concepts into physics.

This objection was later repeated by supporters of the steady state theory, (this basically says that the universe is always expanding but maintaining a constant average density). So this perception was enhanced by one of the originators of the Big Bang Theory, Monsignor Georges Lemaître, who was a Roman Catholic priest.

Evidence

During the 1930s, other ideas were proposed as non-standard cosmologies to explain Hubble’s observations, including the Milne model and the oscillatory Universe (which was originally suggested by Friedmann but advocated by Albert Einstein and Richard Tolman).

However, it was then criticized by the supporters of the steady state theory which says that, if the Universe was really initially as hot as the Big Bang theory suggests, we should be able to find, nowadays, some remainings of this heat.

Eddington and Lemaître

Arthur Eddington agreed with Aristotle that the Universe did not have a beginning in time and that matter is eternal. A beginning in time was kind of “disgusting” to him.

Lemaître, however, said: “If the world has a beginning with a single quantum, the notions of space and time would altogether fail to have any meaning at the beginning; they would only begin to have a sensible meaning when the original quantum is divided into a sufficient number of quanta. If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time.”

Novel Prize 1978 Later on, in 1965, two radio

astronomers discovered a 2.725 degree Kelvin Cosmic Microwave Background radiation (CMB) which pervades the observable Universe. This is thought to be a remnant which scientists were looking for to support the Big Bang Theory. These two radio astronomers shared the Nobel prize for physics for the discovery in 1978.

Expansion of the Universe

Significant progress in Big Bang cosmology had been made since the late 1990s as a result of the advantages in telescope technology as well as the analysis of data from satellites, such as COBE. Cosmologists now have fairly precise and accurate the measurements of many of the parameters of the Big Bang model, and have made an unexpected discovery: ‘the expansion of the Universe appears to be accelerating.

Common misconceptions

When we talk about the big bang theory, many of us think about a huge explotion, but it isn´t, it was (and it is) an expansion. For you to have an idea, rather than figuring a balloon popping and releasing its contents, imagine a balloon expanding, infinitesimally small balloon expanding the size of our current universe.

We tend to imagine the singularity as a little fireball appearing somewhere in space; but according to many experts, space didn’t exist before the big bang took place.

According to calculations, time and space had a finite beginning that corresponded to the origin of matter and energy. The singularity didn’t appear in space; rather, space began inside the singularity. Prior to the singularity, nothing existed, not space, time, matter, or energy-nothing.

THE HIGGS BOSON AND THE BIG BANG

The particle studied by physicists at CERN may also play a role in the Big Bang Theory.

Physicists applied a mathematical principle known as scale invariance – starting with the Higgs boson, they were able to determine the existence of the dilaton, a close cousin, as well as its properties.

the expansion of the current Universe is once again accelerating, but its origins are not understood. This theoretical advance – a completely unexpected result – is reassuring the scientists that they may be on the right track.

Astrophysicists are measuring the state of the Universe today using data from the Planck satellite. They are observing the light echo from the Big Bang, which reveals the large scale properties of the cosmos. In 2013, the measurement campaign will provide results that will be precise enough to compare with the EPFL scientsits' theoretical predictions – and they'll be able to see if their Higgs theory holds up. The boson isn't just hidden in the bowels of CERN's accelerator.

CERN’s acelerator.(ABOVE)Light echo from the Big Bang Theory.

(DOWN)

Hubble’s Law

It is the linear relationship between a galaxy’s distance and ``aparent´´ recessional velocity.

It implies the Universe is expanding.First observational support for Lemaître’s

prediction in 1927.

The American astronomer Edwin Hubble uncovered important evidence that the Universe is expanding.

He compared the measured relative velocities (red shifts) of faraway galaxies with his estimates of their distances from the Earth.

In 1929 he announced his discovery that the further away a galaxy is from another point in space, the faster it appears to recede as the Universe expands - Hubble's Law.

But there was more to be discovered about the expanding Universe - dark energy.

Problems with the Big Bang Theory

1.- The Horizon Problem: discussion of the cosmic microwave background: when we look at the microwave background radiation coming from widely separated parts of the sky, it can be shown that these regions are too separated to have been able to have ever communicated with each other even with signals travelling at light velocity. Thus, how did they know to have almost exactly the same temperature? This general problem is called the horizon problem, because the inability to have received a signal from some distant source because of the finite speed of light is termed a horizon in cosmology. Thus, in the standard big bang theory we must simply assume the required level of uniformity.

2.-The Flatness Problem: present Universe has very low geometrical curvature in its spacetime (it is nearly flat). Theoretical arguments that are well established but too complex to go into here suggest that this is a very unlikely result of the evolution of the Universe from the big bang, unless the initial curvature is confined to an incredibly narrow range of possibilities. While this is not impossible, it does not seem very natural.

3.-The Monopole Problem:The only plausible theory in elementary particle physics for how nuclei in the present universe were created in the big bang requires the use of what are called Grand Unified Theories (GUTs). In these theories, at very high temperatures such as those found in the instants after the Universe was created the strong, weak, and electromagnetic forces were (contrary to the situation today) indistinguishable from each other. We say that they were unified into a single force.

Although there is as yet no certain evidence for the validity of such theories, there is strong theoretical reason to believe that they will eventually turn out to be essentially correct. Our current understanding of elementary particle physics indicates that such theories should produce very massive particles called magnetic monopoles, and that there should be many such monopoles in the Universe today. However, no one has ever found such a particle. So the final problem is: where are the monopoles?