Universe
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Two profound advances in our understanding of the universe date from the 1920s. One was the discovery that the universe is expanding, and that it is immensely larger than our Milky Way galaxy. The other was the revolutionary change from classical to quantum mechanics. The wider implications of these advances are still being explored to this day.
The Universe is expanding, seemingly at a uniform rate, the galaxies are moving back from each other and us. If we run the expansion backwards, we see that there must have been a point in time when all the matter of the Universe was together in an arbitrarily small volume; the occurrence that created our Universe is known to the world as the Big Bang. The Big Bang is the scientific theory that the universe emerged from an extremely dense and hot state about 13.7 billion years ago. At the point of the Big Bang, the universe was substantially dense and unbelievably hot. Just after the big bang, atoms and subatomic particles in a super-dense state were torn apart from each other. If nothing except an outside force acts on these particles, they will continue to expand indefinitely. Even after billions of years, we can still see the effects of this explosion. In 1922, Alexander Friedman discovered the first evidence of an expanding universe. Edwin Hubble established these findings in 1929 when used the Doppler Effect to good use. This was soon after Einstein made a mistake by applying the theory of relativity to the structure of the universe. Hubble showed otherwise. The Doppler Effect simply states that travelling waves will have different frequencies depending on the direction of the object. Hubble in turn used this principle to develop the law of red shifts. Hubble found that galaxies are moving away from us in all directions. As time moves forward, the universe is growing apart. So what this basically means is that if some one actually decides and succeeds in making a time machine and they travelled back in time, the universe would be getting smaller and smaller. The conclusion that he (Hubble) came to was that the universe is expanding in a uniform fashion. When this process is reversed, it is clear that all galaxies in the universe converge to a single point and this is called “a point of infinite density”. This is the main underlying evidence for the hot big bang.
Scientists believe that all forms of matter and energy, as well as space and time itself, were formed at this instant (big bang). We still dont know exactly what came before the Big Bang and therefore “caused” it. At time t=0 a singularity is predicted, where all the laws as we know them, break down. Space and time are infinitely distorted. The uncertainty principle of quantum mechanics prevents any accurate predictions to be made for times less than 10^45 s. The big bang model also teaches that the universe had a beginning.
So we now know that the universe is expanding. Using the general theory of relativity, we can therefore conclude from this data that the universe should be smaller and smaller as one looks back into the past. But this theory only works up to a certain point in time. There is a point in time called the “Planck time” (which is named after the physicist Max Planck, who was one of the pioneers of quantum mechanics) before which our ability to deduce the behaviour of the universe on the basis of general relativity alone is destroyed. The difficulty is that prior to the Planck time, the universe is so small that quantum mechanical effects become very important. Therefore, a correct description of the behaviour of the universe prior to the Planck time requires a mixture of quantum mechanics and general relativity – which we know as a theory of quantum gravity, in other words. Up to now, no full theory of quantum gravity has been developed, much less attained the consensus status that post-Planck-time Big Bang theory enjoys. So without such a theory, we cannot conclude from cosmology any conclusions if the universe had a beginning or not.
As it stands today, the Big Bang is dependent on three assumptions:
1 – The universality of physical laws (for example Newtons theories and Einsteins theory of relativity)
2 – The cosmological principle (at large scale the Universe looks the same in all directions for an observer at any place)
3 – The Copernican principle (this explained that the earth wasnt the centre of the solar system)
There are also three observational pillars that support the Big Bang theory. These are the Hubble-type seen in the redshifts of galaxies, the detailed measurements of the cosmic microwave background, and the abundance of light elements. The Hubbles law is as follows
Hubbles law: V= HoD
Where:
V is the velocity of the galaxy or other distant object
D is the distance to the object and
Ho is Hubbles constant, measured to be 71 ± 4 km/s/Mpc
So these are some of the arguments that support the big bang theory. Another thing is, if the universe was initially very, very hot as the Big Bang suggests, we should be able to find some remnants of this heat. In 1965, Radio astronomers 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 the remnant the scientists were looking for