epepke
Philosopher
- Joined
- Oct 22, 2003
- Messages
- 9,264
Ian said:
Atoms are pretty automatic once you have leptons and quarks. Once you have those, molecules are pretty automatic, too.
However, why exactly are the leptons and quarks the way they are? Why does the proton have about 200 times the mass of an electron? Nobody really knows.
Dr. Fendetestas
Scholar
- Joined
- Jul 20, 2005
- Messages
- 65
BronzeDog said:
A single photon can turn into a pair if its energy (given by E = h · v) is at least the sum of the masses of the electron - positron pair. But that's not the only condition. Pair creation cannot take place in empty space, because momentum would not be conserved. Consider the threshold case where there is just enough energy to create the particles, but not to give them kinetic energy. The momentum would be zero after and non zero before. There must be something (a nucleus) to absorb momentum (the nucleus is so massive compared to the electron that we can consider it only absorbs momentum, not energy). If there are two photons, we wouldn't need a nucleus, provided they have enough energy.
Here's a more thourough explanation.
Edited to add link
Dr. Fendetestas
Scholar
- Joined
- Jul 20, 2005
- Messages
- 65
JamesM said:
What about the spectrum, for example? I'm not sure I know what you mean.
That's a good point.Dr. Fendetestas said:
My argument is as follows: an element is a chemical concept - it's defined as something that can't be further reduced by chemical methods. You don't do chemistry on individual atoms, you have to have sufficient number of them for the chemical properties to become apparent. Look at superatoms as an example - if the number of atoms congregating are sufficiently small, then their behaviour is very different from their usual properties.
An single iron atom doesn't engage in metallic bonding, it's not grey, it doesn't have a melting point or a boiling point, it doesn't conduct. None of the physicochemical properties of elements exists in an individual atom.
But atomic spectra is a good counter example - I hadn't considered a spectrum to be a "property" of an element.
Dr. Fendetestas
Scholar
- Joined
- Jul 20, 2005
- Messages
- 65
Yes, that's what I thought. And it's a perfectly valid point. But we must keep in mind that the spectrum is a very important characteristic. We know the composition of stars, their distance and speed studying them, for example. And it only depends on the atomic structure. However, you are right in saying that things like temperature, boiling point, etc. need more than one atom to make sense.JamesM said:
Mojo
Mostly harmless
Re: Re: Why Do Atoms Exist?
Please tell me that this question was some sort of joke. Please.
Atoms exist. Molecules also exist, and are combinations of atoms joined together.Kumar said:
Please tell me that this question was some sort of joke. Please.
Re: Re: Re: Why Do Atoms Exist?
..............................................
I doubt it's a joke. Isn't the fact of the matter that human beings have got to where they are today by asking why, of everything? What is it that you hear little kids ask a grown -up to the point of obnoxiousness?: "Why?". And then what happens when you give them an answer?: "Why?"
You mean to seriouosly tell me that YOU aren't interested in the 'why's'?
Mojo said:Atoms exist. Molecules also exist, and are combinations of atoms joined together.
Please tell me that this question was some sort of joke. Please.
..............................................
I doubt it's a joke. Isn't the fact of the matter that human beings have got to where they are today by asking why, of everything? What is it that you hear little kids ask a grown -up to the point of obnoxiousness?: "Why?". And then what happens when you give them an answer?: "Why?"
You mean to seriouosly tell me that YOU aren't interested in the 'why's'?
Re: Re: Re: Re: Re: Why Do Atoms Exist?
And, unfortunately, I do not think Kumar was joking. This is why I merely LURK on his threads anymore. I simply do not think he can speak intelligently on the subjects in which he expounds. Whether it is due to lack of intelligence or lack of education is your own call to make, but I think it is the latter, mainly.
Donks said:
And, unfortunately, I do not think Kumar was joking. This is why I merely LURK on his threads anymore. I simply do not think he can speak intelligently on the subjects in which he expounds. Whether it is due to lack of intelligence or lack of education is your own call to make, but I think it is the latter, mainly.
Re: Why Atoms Exist
Actually, technically they didn't come together in the big bang. For hundreds of thousands of years, the universe was only energy, too hot to condense into any form of matter, let alone bound atoms.
It's not that conditions "inside the big bang" led to the formation of atoms and molecules, it's that the physical constants of our universe have certain consequences:
- energy, when it gets cold enough, condenses into particles (and antiparticles: one semi-mystery is why the universe isn't equal parts matter and anti-matter).
- particles, when they get cold enough, bind together into atoms. Atoms are a stabler, lower energy state than free particles.
Ian said:
Actually, technically they didn't come together in the big bang. For hundreds of thousands of years, the universe was only energy, too hot to condense into any form of matter, let alone bound atoms.
It's not that conditions "inside the big bang" led to the formation of atoms and molecules, it's that the physical constants of our universe have certain consequences:
- energy, when it gets cold enough, condenses into particles (and antiparticles: one semi-mystery is why the universe isn't equal parts matter and anti-matter).
- particles, when they get cold enough, bind together into atoms. Atoms are a stabler, lower energy state than free particles.
