Q. "I don't know much about the Big Bang Theory, but it's my understanding that the universe started by some large explosion. What kind of chemicals would have been involved, and how did these chemicals originate in the first place?"  

A. Nobody knows the source of the energy for the explosion, but it was far too large to be chemical or nuclear. Best guess: The origin was in gravitational energy – energy of motion stolen from the energy of gravitational attraction. But it may have been something else – a great repulsion of space itself, with the expansion caused by an early form of dark energy.

So the real answer is: We don't know the source of the energy. In fact, most physicists even think that it is misleading to think of the Big Bang as an explosion of matter. According to the current relativity theory, it was (and still is) space itself that expands – and as space gets large, the distance between galaxies naturally gets larger. The size of galaxies, stars, and atoms does not expand, or we wouldn't notice the change in size of space.

Physicists speculate that the real meaning of the Big Bang was that it was the creation of space itself. Prior to the Bang, no space existed – and no matter within space either. But then again, maybe time also started with the Big Bang – so there was no "prior." These ideas are fun to think about; physicists love to do that; and – if you are worried that you don't understand them – I assure you that neither does anyone else, not really.

Richard Muller is a UC Berkeley professor of physics, a senior scientist at Lawrence Berkeley National Laboratory and the author of Physics for Future Presidents (Norton 2008). The book is based on the lectures for his popular class of the same name, which can be seen on YouTube.

Q. If I found mold on a piece of food, is it safe to break, or cut off the moldy piece and eat the rest?

A. The answer to this question depends upon the food. For bread the short answer is: Throw it away. The mold that you see on the surface of the bread is only a small part of what is there, much of the growth will be invisible. The bread is unlikely to taste very good, and molds can cause allergic reactions and sometimes respiratory problems. Moldy bread is avoidable. Bread freezes very well and thaws rapidly. Store your bread in the freezer, keep out what you can use in a couple of days, and you will never have a problem with molds.

For more information on handling molds you find on other foods, the USDA has an excellent online reference:
www.fsis.usda.gov/pdf/molds_on_food.pdf

Linda Harris is associate director of the Western Institute for Food Safety and Security at UC Davis and a cooperative extension specialist in microbial food safety.

Previous Ask it! questions:

Q. What is the biological or chemical explanation for that feeling I get when I hear a favorite song or see a moving performance, and I get tingles, or goose bumps, on the back of my neck and arms? 

Q. With so many birds in the world, and in our urban environment, you would think we would see dead birds all over the place. But we don't. So, where do birds go to die?

Q: Weight loss is based on expending more energy than consumed, and for every 3,000 calorie deficit you lose one pound. Assuming both an obese person and someone slightly overweight eat proportionate calories and exercise at equal levels, why does the obese person lose a lot more weight in the same amount of time than the slightly overweight person?

Q. Iowa and New Hampshire aren't exactly representative of the nation as a whole and yet they have so much influence on the presidential nominating process. Why are these states first every time?

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