How old are you, Mr. Proton? posted on 2009-03-22
First, a short lesson:
By now most people know what a proton is. Protons and neutrons make up the nucleus of an atom, hence they are called nucleons. The proton is the positively charged nucleon. The neutron has no charge (when I say charge I mean electric charge).
Are nucleons and electrons the smallest constituents of an atom? Certainly not. Some of the more scientifically enthusiastic among us may have heard of quarks. A proton is made up of two up quarks and a down quark, held together by gluons. Atoms are held together by a process of photon exchange between the nucleons and electrons (electric force). Nucleons are held together by a process of gluon exchange (nuclear force).
Now for the conundrum:
If nucleons are made up quarks, then they probably undergo decay when unstable. A neutron left wandering around by itself will decay before too long. Let's say the average lifespan of a free neutron is about 12 minutes. Without the friendly home of a nucleus to live in, the neutron disappears and is replaced by a proton, an electron and an antineutrino.
If neutrons decay, then surely protons will as well. We suspect that a proton will decay into a positrion and a pion. Why do I say "suspect"? Because we don't see it happen. Free protons seem to be very stable little guys. When I say very stable, I mean very, very stable indeed. In fact, recent estimates for the lifetime of the proton put it at 10^32 years, or perhaps higher.
Let's think about that number for a moment. The universe itself, based on cosmology, appears to be maybe 14 billion years old. 14 billion is only 1.4*10^10. The proton, then, seems to last longer than the universe is old...much, much longer!
What does that mean? If the proton lifetime was only, say, 10 billion (10^10) years. On average, one proton out of every 10 billion would decay each year. Your body has maybe 10^30 protons in it. That would mean each year, 10^20 protons would decay. This would be a very small portion of your body. Remember it's only one out of every 10 billion. However, the decay would wreak havok in the same way that radiation causes cancer. You'd be very dead.
So, if protons didn't live stupendously long, we would all be dead. Why do they live so long? I don't know. I don't think anybody understand proton decay. What I do know is that I'm glad they stick around.
By now most people know what a proton is. Protons and neutrons make up the nucleus of an atom, hence they are called nucleons. The proton is the positively charged nucleon. The neutron has no charge (when I say charge I mean electric charge).
Are nucleons and electrons the smallest constituents of an atom? Certainly not. Some of the more scientifically enthusiastic among us may have heard of quarks. A proton is made up of two up quarks and a down quark, held together by gluons. Atoms are held together by a process of photon exchange between the nucleons and electrons (electric force). Nucleons are held together by a process of gluon exchange (nuclear force).
Now for the conundrum:
If nucleons are made up quarks, then they probably undergo decay when unstable. A neutron left wandering around by itself will decay before too long. Let's say the average lifespan of a free neutron is about 12 minutes. Without the friendly home of a nucleus to live in, the neutron disappears and is replaced by a proton, an electron and an antineutrino.
If neutrons decay, then surely protons will as well. We suspect that a proton will decay into a positrion and a pion. Why do I say "suspect"? Because we don't see it happen. Free protons seem to be very stable little guys. When I say very stable, I mean very, very stable indeed. In fact, recent estimates for the lifetime of the proton put it at 10^32 years, or perhaps higher.
Let's think about that number for a moment. The universe itself, based on cosmology, appears to be maybe 14 billion years old. 14 billion is only 1.4*10^10. The proton, then, seems to last longer than the universe is old...much, much longer!
What does that mean? If the proton lifetime was only, say, 10 billion (10^10) years. On average, one proton out of every 10 billion would decay each year. Your body has maybe 10^30 protons in it. That would mean each year, 10^20 protons would decay. This would be a very small portion of your body. Remember it's only one out of every 10 billion. However, the decay would wreak havok in the same way that radiation causes cancer. You'd be very dead.
So, if protons didn't live stupendously long, we would all be dead. Why do they live so long? I don't know. I don't think anybody understand proton decay. What I do know is that I'm glad they stick around.
The Great Tragedy of Science posted on 2009-03-20
"The great tragedy of science - the slaying of a beautiful hypothesis by an ugly fact." - Thomas Henry Huxley
The average layperson would be surprised, I believe, at the current state of hep-th, high-energy physics theory. One might envision physicists arguing about the nature of the universe and its properties, a vision which seems natural enough but for interesting reasons is largely obsolete.
The very concept of a universe has been expanded to a megaverse of which our universe along with its laws of physics represents only a minute portion. The so-called laws of physics are not static, but range widely over a vast number of possible configurations, each configuration giving rise to a unique local universe.
A theorist, then, limits himself not merely to the study of our local laws, but gains insight from studying the laws found in different parts of the megaverse. I am speaking largely of the progress which has been made by using supersymmetry to simplify the terribly complicated mathematics of string theory, giving rise to so-called superstring theories.
Our local universe is not supersymmetric. We appear to have a non-zero vacuum energy. This "ugly fact" may seem to squash the elegant, useful and beautiful simplifications of superstring theory. Nonetheless, great understanding has been gained by exploring the realm of possibilities illuminated by the supersymmetric assumption.
Physicists, therefore, have not merely left the realm of experimentation, but have left the realm as we know it entirely, going forth as explorers into the unknown. Surprise!
The average layperson would be surprised, I believe, at the current state of hep-th, high-energy physics theory. One might envision physicists arguing about the nature of the universe and its properties, a vision which seems natural enough but for interesting reasons is largely obsolete.
The very concept of a universe has been expanded to a megaverse of which our universe along with its laws of physics represents only a minute portion. The so-called laws of physics are not static, but range widely over a vast number of possible configurations, each configuration giving rise to a unique local universe.
A theorist, then, limits himself not merely to the study of our local laws, but gains insight from studying the laws found in different parts of the megaverse. I am speaking largely of the progress which has been made by using supersymmetry to simplify the terribly complicated mathematics of string theory, giving rise to so-called superstring theories.
Our local universe is not supersymmetric. We appear to have a non-zero vacuum energy. This "ugly fact" may seem to squash the elegant, useful and beautiful simplifications of superstring theory. Nonetheless, great understanding has been gained by exploring the realm of possibilities illuminated by the supersymmetric assumption.
Physicists, therefore, have not merely left the realm of experimentation, but have left the realm as we know it entirely, going forth as explorers into the unknown. Surprise!