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.
- What is a singularity? (Beginner)
- Do most astronomers believe in God based on the available scientific evidence? (Beginner)
- Why is looking out into space the same as looking back in time? (Beginner)
- How can I nominate myself for a Nobel Prize in Physics? (Beginner)
- Is the speed of light constant? (Beginner)
- How can we understand the meaning of large numbers like "a million million?" (Beginner)
- What is a dimension? (Intermediate)
- Can you use an infinite line of reflectors to send light to the edge of the Universe? (Intermediate)
- How fast do particles travel in space? (Intermediate)
- Can you fire a gun on the Moon? (Intermediate)
- Is there such a thing as hyperspace? (Intermediate)
- How does melting a material reset its radioactive clock? (Intermediate)
- Could a different theory of gravity explain the dark matter mystery? (Intermediate)
- Would the biggest airplanes cause tsunamis if they crashed? (Intermediate)
- Has there been an experiment that measured speed faster than the speed of light in vacuum? (Advanced)
- What is the difference between the "Doppler" redshift and the "gravitational" or "cosmological" redshift? (Advanced)
- Why can't a plane fly slowly and let the Earth pass underneath? (Beginner)
- Does the Coriolis force determine which way my toilet drains? Does it affect black holes? (Beginner)
- How does the Moon stay "suspended" in the air? (Intermediate)
- What makes a satellite geosyncronise itself with Earth's orbit? (Intermediate)
- Is the gravitational force exerted by the Earth on the Moon equal to the centripetal force acting on the Moon? (Intermediate)
- Where does the kinetic energy of infalling bodies come from? (Intermediate)
- Since Earth is spinning, why do we land in the same place when we jump or fall? (Intermediate)
- What happens to a bullet fired on the Moon? (Intermediate)
- How close do you have to come to the Earth to be influenced by its gravity? (Advanced)
- Do electrons age? (Beginner)
- What causes a particle to decay? (Intermediate)
- What is a graviton? (Intermediate)
- Does quantum entanglement imply faster than light communication? (Intermediate)
- What is the SU(3) quark model? (Intermediate)
- What is the photoelectric effect? Why can't multiple low-frequency photons free an electron? (Intermediate)
- How are photons created and destroyed? (Advanced)
- Can superheavy elements (such as Z=116 or 118) be formed in a supernova? Can we observe them? (Advanced)
The Ask an Astronomer team's favorite links about General Physics:
- Physlink.com: 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.
How to ask a question?
If you have a question about another area of astronomy, find the topic you're interested in from the archive on the side bar or search using the below search form. If you still can't find what you are looking for, submit your question here.