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Name: Tracy J.
Status: student
Grade: 9-12
Location: WA
Country: N/A
Date: 10/12/2005


Question:
I just finished reading an amazing book by Dr. Stephen Hawking (A Brief History of Time). The book was great, but I still have a few questions about Einstein's theory of relativity, specifically of how nothing can travel faster than light. According to one scientist, when the "Big Bang" occurred the universe multiplied itself by 1,000,000,000,000,000,000,000,000,000,000 in just a fraction of a second. Now considering light only travels at 186,000 miles per second, I would think that when the "Big Bang" occurred wouldn't the particles have traveled much faster than the speed of light, which would therefore contradict Einstein's theory of relativity?

This question has been puzzling me for quite some time and I would very much appreciate if you could answer it for me.

This question may have a simple answer, but I have only just started reading about astrophysics, and astronomy. So I am not very well educated on relativity and astrophysics yet.


Replies:
Every physical theory has its limits of applicability. That universal feature distinguishes physical theories from "doctrine" or "dogma" which admits to no exceptions or extensions. The technical term is "falsifiability". Perhaps a better name would be "testability". By either name it means that a physical theory has limits. The theory of relativity is no exception, despite its very wide range of applicability. It is not too surprising that any theory fails under conditions that it was not intended to account for. It is not so much that relativity is "contradicted", rather it does not apply at the conditions in the first few moments post-Big Bang. There is also the issue that the Universe we "observe" is only 5% to 25% (depending upon whose numbers you believe) of the matter and energy required by the behavior of galaxies -- so called "dark energy" and "dark matter". There are still unanswered questions. There is no viable quantum theory of gravity. There has to be a connection, all knowledgeable physicists/cosmologists agree, but no one has put together an acceptable connection.

Even plane (Euclidean) geometry that is taught in all secondary schools has its limits. On the cosmic scale space is curved and space is inseparable from time (relativity). But that does not mean that Euclidean geometry is of no use. It works very well for most of the "stuff" we encounter on a day-to-day basis.

Quantum mechanics is the physics that works on the atomic scale, and it is very different than Newtonian mechanics, but both have their domain. And if you read some "popular" books on quantum theory you will conclude, like famous physicist Richard Feynman, that anyone who says they understand quantum mechanics does not understand the problem.

Keep reading, keep studying, keep an open mind. There is a lot more not understood than is understood.

Vince Calder


Dear Tracy,

A very good question with a rather subtle answer which I have spent some time mulling over without, I feel, achieving full understanding.

The basic answer, however, is quite simple. Nothing can travel faster than the speed of light through space. This does not, however, limit the speed at which space can expand. In the first 1E-35 seconds (that is 0.00..(34 zeroes)..01 seconds after the big bang the universe expanded to a diameter of something like 1 meter carrying all matter with it. So it was expanding something like 3E26 (that is 3 followed by 26 zeroes) times faster than the speed of light! And that includes the matter that was just sitting there at rest in space. Although it is not moving relative to space (whatever that means), a piece of matter can be increasing its distance from another piece of matter at speeds much faster than the speed of light if the space is expanding rapidly enough.

An analogy may help (though analogies are never completely accurate). You have undoubtedly heard of the two dimensional model for the expansion of space where little bugs are sitting on the surface of a balloon as it is being blown up. The separation between the bugs can clearly increase even though the bugs are sitting still.

Best, Dick Plano, Professor of Physics emeritus, Rutgers University


To expand upon my previous comments, see the October 2005 issue of Scientific American. It has a column on higher dimensional space "Beauty of Branes" and an article titled: "Ripples in a Galactic Pond" just in case you think that there is not a lot to learn about the Universe around us.

Vince Calder


Tracy,

What you must first consider is the original size of the universe. An estimate of the speed is distance traveled divided by the time of the event. If the original size of the universe is tiny enough, the distance traveled can be kind of small, perhaps only 1,000 miles. Divide this by a fraction of a second. The speed does not need to be more than 186,000 miles per hour.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College



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