Jump to content

Longest Running Thread EVER


Super Squirrel
 Share

Recommended Posts

Re: Longest Running Thread EVER

 

The dark matter article ... there's a lot of dark matter articles, but I think I heard about this a couple months back. I have to admit I am not that much of a dark matter enthusiast. I'm a radiation guy. I know that astrophysically that is so pre-1960s, but oh well.

*chuckle*

 

is "dark matter" electrons-protons-neutrons that is not enlightened? (serious queston). rephrase: Scientifically, we know what matter is, so in "dark matter" is there matter, or would the phrase "dark energy*" be a more apt term?

 

 

*as opposed to "thingymigig".

Link to comment
Share on other sites

Re: Longest Running Thread EVER

 

No, electrons, protons, & neutrons are not dark matter. Electrons and protons scatter light quite well. Leave a neutron alone for half an hour and it decays into an electron, a proton, and a neutrino. Neutrinos could be dark matter, because they do not interact via the electromagnetic force, only via the weak force and gravity. Neutrinos are, however, matter, because they do experience normal attractive gravity; we have enough ability to detect them and understand their influence on their surroundings to know that. Dark energy is something else. That is a purely speculative construct which doesn't necessarily have to have a normal (that is attractive) response to gravity, and in fact the forms of it that I've heard of being in vogue have repulsive gravity.

Link to comment
Share on other sites

Re: Longest Running Thread EVER

 

No' date=' electrons, protons, & neutrons are [u']not[/u] dark matter.
I think you misunderstood what I was trying to say.

 

We know what matter is: electrons, protons, & neutrons.

 

We don't know what dark matter is. however in the phrase or term dark matter contains the word/term matter, and we know what that is...

 

 

purely a speculative guess, but I think it might have something to do with light. Most great jumps in physics have revolved around the understanding of light. Perhaps light can enlighten dark matter? (pun intentional, but still serious question).

Link to comment
Share on other sites

Re: Longest Running Thread EVER

 

I think you misunderstood what I was trying to say.

 

We know what matter is: electrons, protons, & neutrons.

 

We don't know what dark matter is. however in the phrase or term dark matter contains the word/term matter, and we know what that is...

 

 

purely a speculative guess, but I think it might have something to do with light. Most great jumps in physics have revolved around the understanding of light. Perhaps light can enlighten dark matter? (pun intentional, but still serious question).

Neutrinos (not neutrons) could be the dark matter. They do not interact with the electromagnetic force, period. They do interact with regular matter in ways we can, to some extent, observe. Whether the inferred dark matter is all neutrinos is open to question, because we don't know everything about neutrino physics.

 

It warmed my heart when the measurements of the neutrinos from the Sun that came out in 1990s, allied with the solar structure results provided by the GONG project, categorically proved that the stellar physics guys had been right all along: we really do understand how the Sun works. Since Ray Davis's experiment started running in the mid-1960s, that experiment (which measures one particular subset of neutrinos) consistently found only about 40% of the neutrinos predicted by the solar models. There was a reflex reaction from some of the particle physics people that the problem had to be in the solar model: that is, the stellar physics people were incompetent, or there was some piece of physics that they were leaving out.

 

When other sets of neutrinos could be measured (which took tech developed in the late 1980s), the result was clear. There was nothing that could be done to the solar model that would solve the problem. Every adjustment to the solar model made some aspect of the predicted neutrino flux worse. At the same time, the solar oscillation studies came to a complimentary conclusion: the solar model got the structure of at least the majority of the sun amazingly correct.

 

The resolution was neutrino flavor mixing, that is, on their way out from the solar core, the neutrinos changed type from the one that the early experiments could detect to another one that the experiment could not. In short, it was the neutrinos themselves -- the particle physics, not the stellar physics -- that was causing the bad agreement between observations and model predictions. The particle physics folks are terrifically interested in this, of course; it represents "new physics", that is, stuff that was not predicted because it was so difficult to observe. There is certainly more "new physics" out there with regard to the weakly interacting particles, and for that reason, there's lots of speculation about dark matter including (perhaps as the dominant form of the dark matter) weakly interacting particles that have larger masses than the neutrinos have. At this time, these theories are not much better than speculation, because such particles have not been directly observed (in a way we understand, anyway).

Link to comment
Share on other sites

Re: Longest Running Thread EVER

 

I thought they were supposed to travel AT the speed of light. 'Course I could be wrong...

 

Doc

 

No, photons travel at the speed of light. How fast electrons travel depends on what they are traveling through. How fast they travel around the nucleus of an atom depends on how large the atom is, and which shell they are in. The innermost shell on a large atom like uranium has electrons traveling close to the speed of light. But not AT the speed of light. And the single electron in a hydrogen atom travels more than 100 times slower than that.

Link to comment
Share on other sites

Re: Longest Running Thread EVER

 

do electrons travel around the nucleus of the atom at 9/10ths the speed of light?

 

In general ... no.

 

The speed of an electron in a stable bound energy state isn't something you can determine. When it's in a stable energy state then its total energy content is defined and its angular momentum is defined, but its position and momentum are not.

 

You can do an average over all time for the speed in an energy state. In the low states of the hydrogen atom, the mean speed is 1/137 c. For hydrogen-like (that is, one electron) atoms with more than one proton, that mean speed scales as Z, the atomic number. So taken strictly at face value, if you could get a hydrogenic atom of element 123 or so, that electron would have a mean speed of about 0.9 c. Good luck with that.

 

There are a few states (Rydberg states) where the wavefunction approaches having a "planetary orbit"-like character; that is, the electron has its location probability peak in a "tube" of space on the "equatorial plane" with some fairly tight distribution in both radii. These are the n = large, l = n-1 quantum states.

Link to comment
Share on other sites

Re: Longest Running Thread EVER

 

Turns out we've got a few pieces of old "vaseline glass" -- glass colored with uranium oxide -- at home. My wife dug out a little handheld black light, put new batteries in it, and sure enough, the glass fluoresces that nifty bright green. I need to borrow a geiger counter to see how hot it is in terms of radioactivity ... I don't expect much at all.

Link to comment
Share on other sites

Re: Longest Running Thread EVER

 

Turns out we've got a few pieces of old "vaseline glass" -- glass colored with uranium oxide -- at home. My wife dug out a little handheld black light' date=' put new batteries in it, and sure enough, the glass fluoresces that nifty bright green. I need to borrow a geiger counter to see how hot it is in terms of radioactivity ... I don't expect much at all.[/quote']

 

Then price 'em and insure them!

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...