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Sudbury Neutrino Observatory
Catching neutrinos from the Sun. The Sudbury Neutrino Observatory (SNO) is hardly your average physics experiment: buried in a 2000 meter deep mine in Ontario and filled with 1000 tons of heavy water, its purpose is to catch neutrinos, spritely particles which form in the center of the Sun and usually fly through the Earth without being captured. Recent results from this experiment have solved a long-standing discrepancy; we now know that the number of neutrinos observed from the Sun is equal to the predictions of theoretical nuclear physics and that neutrinos can oscillate between three different "flavors" during the course of their trip.

General Physics

Although our website is about astronomy, we receive many questions that are related, in whole or in part, to the science of physics.

This isn't a surprise, because astronomy and physics are intimately tied together. Physics is the study of the laws that govern the universe, and to the best of our knowledge, those laws are the same here and now as they were long ago and far away.

In order to explain what we see in the night sky, therefore, we appeal to theories originally developed to explain physical phenomena on the Earth. In addition, the extreme environments encountered in astrophysical situations provide a "laboratory" to test these theories under conditions that we could never hope to recreate ourselves.

Physics and Astronomy

Isaac Newton provided one of the first examples of the link between physics and astronomy in the 17th century, when he reasoned that the force of gravity which pulls objects to the Earth is the same force which keeps the Earth and other planets in orbit around the sun.

Later on, in the 19th century, astronomers who were studying stellar spectra (the light from stars split up into its component colors) began to notice that the patterns they saw matched those that occurred when light was shined through different gases in laboratories here on Earth. This discovery allowed astronomers to determine the chemical composition of stellar atmospheres, and in fact, their work later came back to help physicists; the element helium was discovered in spectra from the Sun nearly 30 years before it was found on the Earth.

In recent years, rapid developments in physics and astronomy have kept pace with each other. The twin goliaths of 20th century theoretical physics - general relativity and quantum mechanics - helped explain an enormous number of developments in astronomy, from black holes to cosmology to the various processes by which light is emitted and absorbed in stars, galaxies and the spaces in between. Nuclear physics, meanwhile, predicts and is tested by reactions that take place in the centers of stars, those like the Sun and those undergoing violent events like supernovae.

Despite the above success, there is still much work to be done in physics, especially in the areas that relate to astronomy. General relativity (which deals with massive objects) and quantum mechanics (which deals with small objects) are known to contradict each other, which means we don't currently understand the laws that govern some of the most interesting aspects of our universe - the centers of black holes or the first fraction of a second after the Big Bang.

Physicists continue to seek their holy grail - a unified theory which explains everything in the universe in one fell swoop. One possibile way to reconcile general relativity and quantum mechanics lies in string theory, a theoretical model of the universe still being developed that would involve many more dimensions of space-time than the currently accepted number of four.

Will string theory eventually succeed, or will something else come along to take its place? We don't yet know. But the quest of physicists to understand the universe will continue, and the implications of our increased understanding - on philosophy, religion and society as a whole - will continue to grow.

The Ask an Astronomer team's favorite links about General Physics:

  • a web reference for all types of Physics, including a section in which you can ask the experts. If you think you are an expert you can even try answering the questions yourself!
  • Physics Virtual Bookshelf: Documents on various physics topics written by staff members at the University of Toronto.
  • The official String Theory website: everything you ever wanted to know about String Theory.
  • Cern Public Site: CERN is the European Centre for Nuclear Research - the world's largest Particle Physics centre.

Previously asked questions about General Physics:

How to ask a question:

If you have a question about General Physics which isn't answered above, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.

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