How was the big bang theory developed?

Answer 1

The scientific process just says we shouldn't be afraid of being wrong. We think, we observe, we think again, we model, we check our model to see if it fits what we observe, we conclude, then repeat.

The Big Bang theory is a great illustration of this process because it starts with a simple perspective that only fits a small set of obseration and shows our progression to a more complete perspective that fits more and more observation. I am not a historian and do not know the timeframes of the theories and will definitely skip many theories of the universe because there are way too many to type up in a few hundred words.

First it was the world is flat. Then people noticed you could see the mast from far away, but not the hull. So there must be some curvature. Okay, earth is round.

Observation says that the sun, moon, and local planets do not orbit in perfect circles so they must have elliptical orbits. Still, what is rotating about what?

Years of observation later, we start seeing Jupiter's moons change direction in a cycle kind of pattern, we realize perhaps not everything is rotating about earth. Still no conclusion about that, but even more observations later we see galaxies and we come to the conclusion that earth is rotating on an axis.

Eventually it becomes accepted that the sun is the center of our solar system, planets orbit elliptically, and we may just be a typical star in our own galaxy. There was an interesting argument against an infinite universe. It says if the universe is infinite, there should eventually be light coming from a star at every point in the sky. Thus, since we don't see that, since we have night, we must have a finite universe.

So time passes, more observation. Debates go back and forth, is the universe infinite, finite, expanding, collapsing, stationary, etc. Newton makes earth shattering work on mechanics, his model of mechanics and gravity fit observation the best. It takes years to figure out the implications of his work.

Then someone proves that the previous result of the paradox is wrong if the universe is expanding or collapsing.

Enter Einstein, he fixes any inconsistencies in observations with his general relativity model. Then there is a huge debate about a cosmological constant, or an 'ether'. Is empty space really empty or what? Hubble I think proves that space is expanding because all incoming light is linearly redshifted. Meaning the farther away something is, the more it has been red-shifted.

So, since the universe is expanding, it must have started from some smaller state. Enter Big Bang theory. The big positives of the big bang is it fits the observations:

1) Space is expanding

2) Even background radiation in space

3) probably some others I cannot recall

The story doesnt end there. There are debates on the structure of space, how could a big bang even start, why the background radiation varies slightly from section to section, etc. Theres also a problem fitting the macro with the micro. Quantum physics predicts the micro, special relativity predicts the macro, but theres no crossing of the two. That doesn't make for a very satisfying theory.

Still a lot of questions, but with better technology comes better observations. With better observations, we 'hopefully' get better theories (general relativity wasnt derived from observations, but is extremely accurate). That's just the way of the scientific process.

Answer 2

The Big Bang theory stems from information collected over the years about the speed and direction the galaxies are moving. Once this information was gathered and examined it appeared that every thing was expanding from a certain point. Not all the matter is moving at the same speed, but if you reverse the direction that everything is expanding from, all the material collects into one big mass. Hence the belief that a Big Bang is responsible for the origin of the Universe.

In 1922, Alexander Friedmann noted that the mathematics of General Relativity permit an expanding universe or a contracting universe, but NOT a stable universe. Although Einstein communicated with Friedmann and agreed with his conclusions, nobody made any attempt to connect the math with the actual universe.

Georges LeMaitre independently made a similar conclusion in 1927, but ALSO concluded that the Universe we live in must be an expanding one. He also concluded this meant that, at one point, our Universe must have had (his words) "a day with no yesterday"; and made some speculations on physical evidence that would support his viewpoint, including red shifting of distant nebulae.

In 1930 Edwin Hubble showed that LeMaitre's predictions of red shift was, indeed, correct.