It is all about perseverance

"It's not that I'm so smart. It's just that I stay with problems longer."

Albert Einstein, quoted by Lee Smolin (The trouble with physics, p. 309).

What is a good scientist?

"Good scientists expect that their students will exceed them. Although the academic system gives a successful scientist many reasons to believe in his or her own authority, any good scientist knows that the minute you succumb to believing that you know more than your best students, you cease to be a scientist."

Lee Smolin, "The trouble with physics" (p. 304).

May I always remember this!

Force-carrying particles

I always have had a hard time understanding the concept of force-carrying particles : the idea I had understood was that you can describe the interaction between two particles either by the action of the forces created by the fields associated with each particle, or by new particles that each original particle exchanged with the other, therefore transferring momentum from one particle to the other, hence altering their trajectories. I could make sense of this as long as the interaction was repulsive, as such a momentum transfer would push the particles away from each other. But how could particles get attracted to each other with such a process? This does not make sense to me.

Then, I read the following passage in Lee Smolin book "The trouble with physics" (p. 85): "[...]each gravitational wave could be seen quantum mechanically, as a particle called the graviton - analogous to the photon, which is the quantum of the electromagnetic field."

I thought I had finally understood the concept of force-carrying particle : according to general relativity, the gravitational force is nothing but the deformation of space-time by the presence of mass, which causes objects to move otherwise than in uniform rectilinear motion, hence making us invoke a force, gravity, to explain their motion according to Newton's Second Law. Now, assume that a mass is suddenly placed somewhere in space-time. Its deformation of space-time will propagate at a finite speed, that of light, making its effect felt at greater and greater distances. These are gravitational waves. In analogy with electro-magnetic waves, which are quantized in photons, gravitational waves are quantized in gravitons, which are therefore the particles "carrying" the gravitational force, i.e., making its effects felt at distance.

This at last made sense to me. But then I watched the DVD version of Brian Greene's book "The elegant universe", in which there is an animation showing two persons throwing small balls at each other, and getting attracted toward each other as they throw the balls harder and harder. So we are back to this idea of momentum exchange, and this does not make sense to me for explaining attractive forces such as gravity!

Is there a theoretical physicist around who could help me understand this better?

What kind of scientist are you?

"As I reflect on the scientific careers of the people I have known these last thirty years, it seems to me more and more that these career decisions hinge on character. Some people will happily jump on the next big thing, give it all they've got, and in this way make important contributions to fast-moving fields. Others just don't have the temperament to do this. Some people need to think through everything very carefully, and this takes time, as they get easily confused. It's not hard to feel superior to such people, until you remember that Einstein was one of them. In my experience, the truly shocking new ideas and innovations tend to come from such people. Still others — and I belong to this third group — just have to go their own way, and will flee fields for no better reason than that it offends them that some people are joining in because it feels good to be on the winning side. So I no longer get bothered when I disagree with what other people are doing, because I see that temperament pretty much determines what kind of science they will do. Luckily for science, the contributions of the whole range of types are needed. Those who do good science, I've come to think, do so because they choose problems that are suited to them."

Lee Smolin, "The trouble with physics" (p. 95).

I think I belong to the second group of scientists who need to think through everything very carefully and get easily confused, although don't expect shocking new ideas and innovations to come out of me! What about you, dear reader?

How do you know whether you have really understood something?

"The physicist Ernest Rutherford once said, in essence, that if you can't explain a result in simple, nontechnical terms, then you don't really understand it. He wasn't saying that this means your result is wrong; rather, he was saying that it means you do not fully understand its origin, meaning, or implications."

Brian Greene, "The elegant universe" (p. 203).

This rejoins this famous French quotation:

"Ce que l'on conçoit bien s'énonce clairement,
Et les mots pour le dire arrivent aisément."

Nicolas Boileau, "L'Art poétique".