MadSci Network: Astronomy

Re: I would like to know if this theory is legitimate

Date: Fri Feb 28 21:13:20 2003
Posted By: Bryan Mendez, Education and Public Outreach Scientist
Area of science: Astronomy
ID: 1045511045.As

I have made a theory that proves the Big Bang Theory wrong, and I would just like to know if it is legitimate. The theory states that the universe was infinitesimally small. If it were so, then in order for it to expand, it would have to be expanding at a speed greater than infinity. (Infinity+1=infinity) Since it is not possible for anything to move at a speed greater than infinity, how is it that the universe could expand? Moreover, if it could expand, it would be at a VERY slow speed/velocity, the theory states that at one second, the universe was infinitesimally small, and the next it was billions of light years across. (For it to be billions of light years across, it would have to be moving at a tremendously great speed.)

Hello, Colby,
First things first. In science, the word "theory" means some thing very specific and different from common usage. A theory is the generally accepted model for describing or explaining a phenomenon. A theory has stood up to rigorous testing and investigation for many years. A theory is well supported by observed facts. Theories usually begin life as a hypothesis, one of many possible explanations for a phenomenon. Then as the other hypotheses are eliminated through scientific investigation the one that survives all the others usually becomes the working theory. So, when people casually tell you about their "theory," what they are really talking about is just an idea or hypothesis. It is important to be clear on that so that you understand that when you hear about the Big Bang Theory, the Theory of Quantum Mechanics, the Theory of Relativity, or the Theory of Biological Evolution, you know that these are the best explanations that we currently have for nature and they are backed up by evidence. Secondly, a hypothesis (or theory) cannot disprove a theory. The only thing that can disprove a theory is physical evidence.  In science, for a hypothesis to be legitimate it must be, in principle, disprovable by evidence. In other words, a hypothesis must be framed so that if it is incorrect it can be shown by experiment. Evidence can never positively prove a hypothesis or theory, it can only show consistency with the idea.

So, on to your question specifically. The Big Bang Theory does not actually state that the Universe was infinitesimally small at the beginning. Such a mathematical point is called a singularity and our theories of physics (quantum mechanics and relativity) cannot accurately account for them. The Big Bang Theory states that since the Universe is currently expanding (as is directly observed) then it must also have been expanding in the past but have been smaller more dense and hotter. This idea is well supported by observations of the Universe at very great distances (which means at times long ago because of the finite speed of light), and especially the cosmic microwave background radiation which comes from a time when the whole Universe was as hot and dense  as the surface of a star. The Big Bang Theory itself does not contain any explanation for why it was expanding. It only assumes that it was and we use our understanding of relativity and quantum mechanics to figure out what the Universe was like at earlier and earlier times. There is a point where our physics breaks down and we are not currently able to run the cosmic movie back in time any further. At a time of 10-43 seconds after expansion began is the earliest time we are able to understand. Before that we have no working theory for how time, space, matter, and energy work. It's called the "Planck time" after a scientist who had a major role in the development of quantum mechanics. At the Planck time the Universe has a finite size and density. So the problem of dealing with a singularity does not arise.

The last thing I would mention is that in the Big Bang Theory it is space itself that expands, and there is no restriction in any of our theories on how fast space can expand. Space can expand faster than the speed of light and there are some hypotheses being studied suggesting that the Universe may have expanded at such incredible speeds very early on in that first second, shortly after the Planck time. The hypotheses are generally called Inflation.

Thanks for your question and keep thinking those big thoughts!

-Bryan Méndez

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