March 15, 2010

Big Bang for beginners-2: The nature of energy

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)

For previous posts in this series, see here.

In order to understand the Big Bang theory, we also need to have an understanding of the nature of energy in addition to that of matter that was discussed yesterday. The word 'energy' has a technical meaning in science but has also entered into the vernacular and thus has been used to mean many things. In everyday language, it usually signifies the source of the ability to do things, such as move objects or break them up or put them together. So gasoline provides the energy to run cars, coal the energy to heat things, and so on.

Energy takes many forms. Some of it comes from the motion of objects that have mass. For example, the energy associated with the motion of a speeding car can be used to break through a fence. Wind energy comes from the motion of air and can be used to power wind turbines. Water waves in the form of tsunamis can carry vast amounts of energy that can wreak widespread destruction. Some energy is stored as chemical energy in certain kinds of matter such as gasoline and coal that are released under certain conditions. Nuclear energy is what is stored in atomic nuclei. All these forms of energy are associated with things that have mass.

But there is a form of energy that is not associated with any mass. Electromagnetic energy refers to energy that is not associated with a tangible object that has mass but still has the ability to do things. In everyday language, we do not use the term electromagnetic but instead refer to this kind of energy according to the source that produces it. Sunlight is one such case. It has no mass but it has energy (what we call solar energy) and can heat objects, as anyone who has been warmed by the Sun can testify. A microwave oven produces a similar massless energy that we use to cook food. X-ray machines also produce massless energy that we can use to see through some things. Radio waves are another form of massless energy.

All these different forms of massless electromagnetic energy differ only in how much energy is carried by a single unit of that energy. The name given to this single unit is the 'photon'. The energy that can be carried by a photon varies continuously and the popular names we assign, such as microwave, radio, visible light, X-rays, refer to ranges of photon energy that are based on somewhat arbitrary boundaries. So a photon in a radio wave has less energy than a photon produced by a microwave oven, which has on average less energy than a photon of sunlight, which in turn has less average energy than a photon produced by an X-ray machine.

The energy of each photon is tiny but any energy source that has an observable effect in everyday life, such as sunlight and microwave ovens, contains enormous numbers of them.

So to summarize in terms of increasing energy of photons:

radio waves→microwaves→sunlight→X-rays→ …

In scientific research, we often use photons to break matter up into its smaller constituents because photons can be aimed extremely precisely at small targets. In yesterday's post I described a hierarchy of constituents of matter in order of decreasing size.


I also said that it takes larger and larger amounts of energy to break up the smaller constituents. If we use photons for this purpose, then we can split a molecule into atoms using a low-energy photon, while we would require a higher energy photon to split up an atom into nuclei and electrons, and yet higher energy photon to break up a nucleus into protons and neutrons. We have not as yet produced in laboratories or accelerators photons that have high enough energy to break up protons and neutrons into free quarks and gluons, assuming that this can be done at all.

As far as we know, there is no upper limit to the energy that a photon can have, just as we do not know if there is a lower limit to the size of the basic constituents of matter. In both cases, our knowledge is limited by our present technology to produce the required energies in the laboratory. There are photons with extremely high energy (many orders of magnitude larger than anything we can produce in the laboratory) that come to us from outer space in what are called cosmic rays but we cannot corral them to use them in controlled experiments.

With these preliminaries out of the way, we can begin to explain the Big Bang theory.

POST SCRIPT: Art films

Monty Python made an art form of parodying BBC-style interviews and in this clip That Mitchell and Webb Look pay homage to them and take on pretentious films and their directors.


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