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Theoretical physics, anyone else like it?

Posted: Fri Oct 20, 2006 11:37 pm
by akimm
I just love to discuss physics, so if anyone else is game, i'd be willing to hold a discourse.

I know this is a PHP forum for the most part, but I figure general discussion is ok, if not delete this, I hold no grievance.

Posted: Sat Oct 21, 2006 11:41 am
by LiveFree
Well, Im not sure how much of a disucssion we can have here but I do have few bar bets:

1. You are radioactive
2. Space is not as frigid as wel all think it is
3. The sun does not grow in size when it rises/sets (from our prespective)

Posted: Sat Oct 21, 2006 2:30 pm
by feyd
I'm usually more interested in the concrete physics, but I can dabble in the theoretical.
  1. From my understanding, we, on a technical level, are radioactive, as is everything around us.
  2. Space has no temperature. The temperature of an object will vary depending on where it is in relation to radiation sources, but suffice it to say, it's very near absolute zero when there are no near radiation sources.
  3. Gravitational optics may play tricks on our eyes, but any further, and I'm not too sure.

Posted: Sat Oct 21, 2006 2:33 pm
by Christopher
feyd wrote: [*]Gravitational optics may play tricks on our eyes, but any further, and I'm not too sure.[/list]
I think atmospheric optics may play a part in this ... but the actual bodies obviously do not change size.

Posted: Sat Oct 21, 2006 2:38 pm
by John Cartwright
feyd wrote: Space has no temperature. The temperature of an object will vary depending on where it is in relation to radiation sources, but suffice it to say, it's very near absolute zero when there are no near radiation sources.
I'm a bit confused about your explanation. Temperature is an interval measurement, meaning 0 does not mean no temperature. So how can zero radiation mean zero temperature?

Posted: Sat Oct 21, 2006 2:41 pm
by feyd
Jcart wrote:I'm a bit confused about your explanation. Temperature is an interval measurement, meaning 0 does not mean no temperature. So how can zero radiation mean zero temperature?
Background radiation, where objects become largely undetectable to us in space has a temperature just a hair above absolute zero. Space itself doesn't have a temperature because there's nothing to heat.

Posted: Sat Oct 21, 2006 2:43 pm
by Chris Corbyn
Jcart wrote:
feyd wrote: Space has no temperature. The temperature of an object will vary depending on where it is in relation to radiation sources, but suffice it to say, it's very near absolute zero when there are no near radiation sources.
I'm a bit confused about your explanation. Temperature is an interval measurement, meaning 0 does not mean no temperature. So how can zero radiation mean zero temperature?
This is interesting. 0 depends upon your units. 0 kelvin is taken to be the minimum possible temperature at least from the materials we know of.

It's all related to entropy in a substance. If atoms continue to move then it will have a temperature above zero kelvin. If they don't move at all it's likely zero or very close to zero kelvin. For atoms to stop moving entirely they pretty much need to be touching each other and they really don't want to get that close. Absolute zero is what we call zero kelvin and is basically a fairly simple calculation based upon a nice linear correlation for temperature vs entropy if I remember correctly.

EDIT | So in theory, as per feyd's last post if space has no matter (dark matter anybody???) then it will have no temperature as their are no atoms to move and therefore no entropy.

Posted: Sat Oct 21, 2006 2:50 pm
by John Cartwright
Interesting :P

Posted: Sat Oct 21, 2006 3:12 pm
by Chris Corbyn
http://en.wikipedia.org/wiki/Absolute_zero

Read the bit about negative temperatures ;)

EDIT | I knew the law was on the tip of my tongue. It's the ideal gas law: http://www.iop.org/Our_Activities/Schoo ... _5412.html (see the graph)

Posted: Sat Oct 21, 2006 5:17 pm
by LiveFree
1. If you have ever ingested any part of a plant, you contain a small amount of Carbon 14 (used in carbon dating). Of all the amount of carbon that a plant takes in, a small part of that itake is of C14.

2. (Please note I may not have this 100% correct). Keep in mind, in physics, "cold" does not exist. It is a gramatical phrase used as a negative adjective for showing that something has less heat than a comparing object. What is heat? Heat is the energy created by the matter of an object moving around and colliding with one another. What is space? A vacumn, which has no matter. If there is no present matter, no heat can exist. So you ask, then why can the Space Shuttle sometimes get as cold as -100F? Its because the Space Shuttle has matter. It loses heat and gains heat (through radiation) like any other object.

3. It has nothing to do with the atmosphere. It is a simple fact of us comparing the rising sun to our surroudnings.

Im not a physics professor, but I believe what I have said above is firmly groudned in elementary physics.

EDIT: I just realized I just re-stated a lot of what d11 said.

Posted: Sat Oct 21, 2006 5:25 pm
by Chris Corbyn
You're right about the rising sun/moon thing. It's just our eyes playing tricks based on objects around the thing we're looking at. That's not to say things don't look different lower in the sky than they do higher. The atmosphere has an effect on the way we see colors. Why is the sky blue? Why does it look red when the sun starts to set? Why the sky on mars red? (I know these answers by the way) :)

Posted: Sat Oct 21, 2006 5:26 pm
by LiveFree
You're right about the rising sun/moon thing. It's just our eyes playing tricks based on objects around the thing we're looking at. That's not to say things don't look different lower in the sky than they do higher. The atmosphere has an effect on the way we see colors. Why is the sky blue? Why does it look red when the sun starts to set? Why the sky on mars red? (I know these answers by the way) Smile
And the nice volcanic gas that casues those blue moons ;) (seriously)

Posted: Sat Oct 21, 2006 5:27 pm
by Chris Corbyn
Ok then. This has some theories that are commonly used in seriosu physics work but they are just that; theories -- hypotheses that seem to fit.

Is light made up from matter or is it just a form of energy?
If light is made up from matter, are other forms of energy made from matter?

You might want to read about particle-wave theories and then think about the effects of black holes on light in close proximity.

Posted: Sat Oct 21, 2006 5:30 pm
by timvw
Why is the sun yellow (on earth) ? http://en.wikipedia.org/wiki/Rayleigh_scattering

Posted: Sat Oct 21, 2006 6:26 pm
by akimm
A few of your dabbled with the phrase absolute zero, but just remember, anything that is absolute zero has no mass(so it has been claimed) and considering the fact that without mass something doesn't exist

Why is the sun yellow (on earth)
because of temperature of the Star I believe, since it still has plenty of H left it burns at a very hot temperature..

Is light made up from matter or is it just a form of energy?
If light is made up from matter, are other forms of energy made from matter?
Form of energy I believe, made of packets of energy called photons, yes I believe its very plausible to say other forms of energy are made from matter.