Wednesday, June 22, 2011

Quote of the Day

First Quote of the Day:
"The notion of particles as objects in space, taken of from classical physics, is thereby eliminated…." —Aage Bohr, son of Niels Bohr and also a Nobel Prize winning physicist, and Ole Ulfbeck denying the existence of atomic scale particles, i.e. saying atoms don't exist.

Obviously, he is not saying that atoms don't exist as a mathematical construct or as a different notion, but that they don't exist as classical particles. He is saying that an alpha particle does not travel through space to register on a geiger counter the same way a ball travels through space to arrive in your mitt or the way a particle of dust travels to your coffee table.

Second Quote of the Day:
"A particle is simply a physical system that has no continuous degrees of freedom except for its total momentum." —Steven Weinberg, also a Nobel laureate in physics.

He goes on to explain, "For instance, we can give a complete description of an electron by specifying its momentum, as well as its spin around any given axis, a quantity that in quantum mechanics is discrete rather than continuous. On the other hand, a system consisting of a free electron and a free proton is not a particle, because to describe it one has to specify the momenta of both the electron and the proton— not just their sum. But a bound state of an electron and a proton, such as a hydrogen atom in its state of lowest energy, is a particle. Everyone would agree that a hydrogen atom is not an elementary particle, but it is not always so easy to make this distinction, or even to say what it means."

Obviously these two physicists disagree, but I think their disagreement is with the definition of a particle.


Big Myk said...

Everything we call real is made of things that cannot be regarded as real. Niels Bohr

Big Myk said...

Perhaps more to the point: We must be clear that when it comes to atoms, language can be used only as in poetry. Niels Bohr

James R said...

Those are much better quotes. I never realized how poetic Niels Bohr was.

Big Myk said...

Let me add two more: one is something you and I have been trying to say for years but never so succinctly and eloquently: "Physics is to be regarded not so much as the study of something a priori given, but rather as the development of methods of ordering and surveying human experience."

And the second is a classic in itself: "No, no, you're not thinking; you're just being logical."

Finally, if you think Bohr might be one of the more profound thinkers of the modern age, you are in good company. John Wheeler, the physicist who coined the term Black Hole, had this to say about his time working with Bohr: "You can talk about people like Buddha, Jesus, Moses, Confucius, but the thing that convinced me that such people existed were the conversations with Bohr."

James R said...

I once read a very articulate article from a physicist who wrote about how, as a graduate student, the big draw of physics was that you were on the cutting edge of discovering the secrets of the universe. What other profession would you choose?

As a wise, experienced physicist (and here is where I wish I had his words as they may have been even better than Bohr's) he said something like, you realize you do not so much discover the secrets of the universe as much as explain them.