How do scientists know for sure that the Big Bang actually happened?

Question

Also, are there any other theories of how the universe was created?
And the Big Crunch theory is the most popular theory for 'the end'. But do we know for sure that the universe is going to collapse into itself (like penrose and hawking proved and not like Einstein said that it 's gonna miss itself and expand once again) and not keep on expanding and eventually fall apart etc. ?
And if the Big Crunch does occur what do u think will happen?
(facts, personal theories)

Answer 1

Your question would be best divided into several questions for a more thorough and less lengthy answer.

http://ssscott.tripod.com/BigBang.html

The Universe is 13.7 billion years old. This age is scientifically determined using star ages, star distances compared to their speed of recession, and by using the location of the first acoustic peak in the microwave background power spectrum to determine the size of the decoupling surface (size of universe at the time of recombination). The light travel time to this surface (depending on the geometry used) yields a reliable age for the universe within an error of 1%. SOMETHING happened around 13.7 billion years ago.

http://en.wikipedia.org/wiki/Lambda-CDM_model

What are the major evidences which support the Big Bang theory?

First of all, we are reasonably certain that the universe had a beginning. Second, galaxies appear to be moving away from us at speeds proportional to their distance. This is called "Hubble's Law," named after Edwin Hubble (1889-1953) who discovered this phenomenon in 1929. This observation supports the expansion of the universe and suggests that the universe was once compacted. Third, if the universe was initially very, very hot as the Big Bang suggests, we should be able to find some remnant of this heat. In 1965, 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 which scientists were looking for. Penzias and Wilson shared in the 1978 Nobel Prize for Physics for their discovery. Finally, the abundance of the "light elements" Hydrogen and Helium found in the observable universe are thought to support the Big Bang model of origins.

Evidence of the Big Bang:the thermal spectrum of the cosmic microwave background radiation appears hotter in distant clouds of gas. Since light travels at a finite speed, we see these distant clouds at an early time in the history of the universe, when it was more dense and thus hotter.

The distribution of matter in the universe is nearly the same throughout. This would imply a common starting point. And is further signified by the fact that space is expanding between galaxies and each galaxy would see the same expansion.

The relative proportion of light elements in the universe is a close match to predictions for the formation of light elements in the first minutes of the universe, according to Big Bang nucleosynthesis.

Other creation theories: There are the three fundamental theories of the universe, how it started and how it ends. These are the Big Bang Theory, the Stady State Theory and the Cyclic Universe Theory. There are many others including the God theory.

Also, WITHIN the Big Bang theory there are many theories. The Big Bang theory has gone through many changes as it has evolved in the last 60 years.

The Big Crunch: I would offer my disagreement that the Big Crunch is the most popular theory of the end. It is my understanding that the most widely accepted theory is the Big Freeze. There exists no evidence that the Universe will stop expanding and collapse into itself. On the contrary, observational evidence shows that not only does the Universe continue to expand, but it is expanding at an ever increasing rate!

For the Big Freeze theory to happen, the shape of the Universe must be either hyperbolic or flat. If it is hyperbolic, which is usually pictured as a saddle shape, then the density must be lower than the critical density (which is approximately three hydrogen atoms per cubic meter), which means that the universe isn't heavy enough to collapse under gravity. If our Universe is flat, then the density will be exactly at the critical point, preventing the universe from collapsing as well. If the universe is heavier than the critical point, it will result in a shrinking universe, which leads to another theory, called the Big Crunch. For the Big Crunch to occur, the shape of the Universe would have to be spherical. The problem with measuring the current density of our Universe is that we cannot see most of the matter in it, and it is theorized that most of the universe may be made up of dark matter, a hypothetical, invisible form of matter in space.

The Cyclic theory might be supported by Hawking and Penrose but it is not a theory held by the majority and it most certainly HAS NOT been proven.

As I am not a proponent of the Big Crunch theory, I offer no opinions as to what happens afterward.

It is my view that the Universe will continue to expand.

Answer 2

The best evidence that the big bang happened is the cosmic microwave background. This is a bath of microwaves that fills the entire universe.

Way back at the time of the big bang, the universe was fairly uniformly filled with hydrogen and helium gas. This gas was dense and very hot. It was so hot that the electrons in the gas didn't stay bound on the atoms. The gas gave off light, as all hot things do, in a characteristic pattern. These free electrons absorbed any light that was moving around in the universe before the light could travel very far.

Before long the gas cooled down enough that the electrons would bind to the atoms. This made the universe transparent, and the light that the gas was emitting got released and was free to travel through the universe. As the universe continued to expand, the light lost energy and was shifted into the microwave. Some of this light is still traveling through the universe today, and that's the cosmic microwave background.

The CMB should have specific properties predicted by cosmology, and measurements have shown that the agreement is perfect. There are few examples in astrophysics where theory agreed so perfectly with observation. This makes the big bang very secure indeed.

It's looking like the big crunch isn't how the universe is going to end after all. There are three different ideas about what the geometry of the universe might be: flat, spherical, and saddle-shaped. Only the spherical universe ends in a big crunch. It's difficult to tell which is the right geometry, because it's really close. That's without dark energy. About a decade ago, astronomers realized that this "dark energy" is pushing the universe apart. So a big crunch is even less likely.

It's hard to say what would happen if a big crunch did happen. It might be that the universe would pop out of existence. Or maybe there would be a rebound and the universe would start over again. The big bang doesn't really cover that, and we'll need new physics before we understand what would happen.

Answer 3

The scientist do not know for sure that the Big Bang 'happened'.

What they know is that the universe is expanding and that there is a direct relationship between a distant object's distance and its recession speed.

From that, some priest astronomer came up with the Primordial Atom hypothesis and others used it to structure a theory to explain how the universe could have evolved from a state of very high density and temperature, to what we see today.

A theory is neither true nor false. A theory is more useful or less useful. It uses tested rules to make predictions about what we should find, given certain conditions. It just happens that of all the available choices, the theory now called Big Bang (with some modern revisions) is the most useful.

The theory itself explains what happens from a certain time (NOT time zero) up to now. It becomes totally useless if you try to push it back further than the Planck time (very soon AFTER the 'start' whatever that was).

Big Bang predicts a Big Crunch if, and only if, the density of matter (baryonic and dark together) is above some critical value. Based on the most recent observations, it would appear that the density of the universe is not sufficient to bring about a Big Crunch. The universe will keep on expanding.

If there were a Big Crunch, and if it were somewhat symmetrical to the Big Bang (at least in terms of temperature or density), then there would be a Planck Temperature past which the Big Bang (a.k.a. Big Crunch) theory would become useless as a prediction tool.

Many who have thought about this think that a Big Crunch 'could' be the trigger for the next Big Bang. But we do not KNOW. We can only guess for now.

Answer 4

"why do so many scientists believe in the big bang, why not put their reputations on the line, study it, and try and come up with something new" You don't come up with something new just because. It has to make sense. At this time, the Big Bang theory is the best explanation of the various observations made in the universe, such as the background radiation observed by radio telescopes. And the origin and development of the Universe is still being studied, but so far, nothing has come to light that would displace the Big Bang as an invalid theory. And simply mentioning important people is an appeal to authority, a fallacious argument.

Answer 5

they do not know "for sure" so to speak; but evidence does point to it. Theoretical support for the Big Bang comes from mathematical models, called Friedmann models. These models show that a Big Bang is consistent with general relativity and with the cosmological principle, which states that the properties of the universe should be independent of position or orientation.
Observational evidence for the Big Bang includes the analysis of the spectrum of light from galaxies, which reveal a shift towards longer wavelengths proportional to each galaxy's distance in a relationship described by Hubble's law. Combined with the assumption that observers located anywhere in the universe would make similar observations (the Copernican principle), this suggests that space itself is expanding. The next most important observational evidence was the discovery of cosmic microwave background radiation in 1964. This had been predicted as a relic from when hot ionized plasma of the early universe first cooled sufficiently to form neutral hydrogen and allow space to become transparent to light, and its discovery led to general acceptance among physicists that the Big Bang is the best model for the origin and evolution of the universe. A third important line of evidence is the relative proportion of light elements in the universe, which is a close match to predictions for the formation of light elements in the first minutes of the universe, according to Big Bang nucleosynthesis.

Most scientists believe the universe will keep expanding till eventually no more stars are formed and the universe just goes dark soto speak

Answer 6

Firstly, the Big Crunch theory is no longer the most popular amongst scientists. The Big Rip is now the commonly accepted in the astrophysical community. Galaxies continue to move apart, everything continues to move apart until the gravitational attractions are overpowered by dark energies, and all things implode on their own gravity.
Scientists accept that the Big Bang occurred because it is the only way they can explain how something can exist at all. The Big Bang theory, although proposed by a Catholic priest, is supported by the laws of quantum mechanics, which is the most popular explanation for everything in contemporary Physics.

Answer 7

Nobody knows 'for sure' that the Big Bang happened. However, the observed present conditions of the universe support the BB theory better than any other concepts.

"...the Big Crunch theory is the most popular theory for 'the end'..."
Not true..! The most widely accepted theory about the fate of the universe, particularly data returned by the WMAP mission, is that it will continue to expand indefinitely.

Answer 8

The accidental discovery of CMB radiation by Penzias and Wilson at Bell Labs, provides pretty good support for the Big Bang theory. I've never heard of the Big Crunch theory being the most popular theory outside of newspapers that need a story before the deadline, especially since the rate of universal expansion is increasing instead of decreasing. This makes the Big Crunch theory implausible as measured by our current level of technology. Here's a quick site that details some of the support for BB theory in fairly understandable terms.

http://map.gsfc.nasa.gov/m_uni/uni_101bbtest3.html

Answer 9

A new theory is emerging. It states that matter did not come from one single volume in a great explosion, but was allowed to come into being at different intervals over different regions. This is keeping in line with Hubble's discovery of an expanding universe, Heisenberg's principle of uncertainty and Schrodinger's equation of position. It doesn't predict an end, only a beginning.

Answer 10

Imagine you are driving home from church and you come across two cars smashed into each other at Elm and Main Street. You get out and see the drivers exchanging information. You ask a bystander who says everybody heard the crash but no one actually saw it. That's the Big Bang; all kinds of circumstantial evidence but no eye witnesses.