NationStates Jolt Archive

Since almost every thread in this forum is either political or religious, let's talk about something else.

"And now, for something completely different!"

Anyone here interested in astrophysics or quantum physics? I find both quite interesting.

Astrophysics is pretty sweet until you get into Einsteinian gravity, then blood starts to leak from my ears and I spout jibberish. Quantum mechanics makes my brain hurt.

That's why I love it! It makes everyone else's brain hurt!

I believe that a very esteemed scientist once said, "Nobody understands quantum mechanics."

yes, i am interested. Explain gravity to me. I had someone do that before, but i got it for a second and then it leaked out. Maybe you can explain it better.

Peace Always,
Talf Yeknom of Yeknomia

gravity is like an imprint in time/space. The space around an object is bent toward it. LOL

I love astrophysics

Yeknomia, did they use the sheet-and-ball model? It's often used to explain gravity in laymen's terms... I.e., you hold out a sheet, stretched nearly taught. This represents the time-space continuum -i.e. "existence." Place a bowling ball in the center of the sheet. This bowling ball represents a mass, any mass -for example, a planet. Take a tennis ball, this represents a smaller mass(say, a spaceship).

If you rolled the tennis ball along the flat sheet(before you put the bowling ball there), it would roll in a straight line -because there is no gravity to interfere with its velocity. But, if you rolled the tennis ball along the sheet while the bowling ball was dragging the sheet down, the tennis ball would spiral downwards towards the bowling ball. This is (in an extremely simplified manner) how gravity works -it warps space, basically.

As to what is it? What causes it? That's pretty much anybody's guess at this point...

I find them interesting, yet thinking about it all too much hurts my brain. A lot.

Although sometimes I enjoy making my brain hurt...

Gravity is fun. The force of attraction between all matter. Of corse the force is greater with larger masses and when the distance between the masses is smaller. It can be summarized in the formula:

F = G(m1)(m2)/r^2

where G, the universal gravitational constant is 6.67*(10^-11) N*m^2/kg^2.
m1 is the mass of the first object in question, and m2 the second, both measured in kg. And finally, r, being the distance between the two objects, or if you prefer, radius, measured in meters.

Quantum mechanics makes my brain hurt.
Wavefunctions. Oy! I never really had a good grasp on wavefunctions.

--The Democratic States of Cogitation

physics was the only subject I passed in year 12. I remember doing an essay on dark matter, but I don't remember much about it.

Gravity is fun. The force of attraction between all matter. Of corse the force is greater with larger masses and when the distance between the masses is smaller. It can be summarized in the formula:

F = G(m1)(m2)/r^2

where G, the universal gravitational constant is 6.67*(10^-11) N*m^2/kg^2.
m1 is the mass of the first object in question, and m2 the second, both measured in kg. And finally, r, being the distance between the two objects, or if you prefer, radius, measured in meters.

I cant wait till they figure out quantum gravity...

damn

Yeknomia, did they use the sheet-and-ball model? It's often used to explain gravity in laymen's terms... I.e., you hold out a sheet, stretched nearly taught. This represents the time-space continuum -i.e. "existence." Place a bowling ball in the center of the sheet. This bowling ball represents a mass, any mass -for example, a planet. Take a tennis ball, this represents a smaller mass(say, a spaceship).

If you rolled the tennis ball along the flat sheet(before you put the bowling ball there), it would roll in a straight line -because there is no gravity to interfere with its velocity. But, if you rolled the tennis ball along the sheet while the bowling ball was dragging the sheet down, the tennis ball would spiral downwards towards the bowling ball. This is (in an extremely simplified manner) how gravity works -it warps space, basically.

As to what is it? What causes it? That's pretty much anybody's guess at this point...

Kindof a cyclical definition isn't it? I mean, you're using gravity acting on balls and a sheet as an analogy for gravity.

not that I don't describe it that way myself mind you...

Astrophysics kicks ass, as does QM and cosmology. And eveybody's favorite General relativity.

m= mo/sqrt(1-(v/c)^2). Go mass increase.

Well, I'm not sure how it's circular... The "gravity" in the analogy is represented by the curvature on the sheet(space-time continuum), caused by the bowling ball(planet's mass). Gravity and mass are directly related, yes, but they are discussed as two separate things AFAIK(in the interest of keeping the discussion accurate).

But no, it's not a very definitive analogy. Like I said, it's just laymen's terms.
EDIT: Never mind, I see what you meant. Yes, it's circular logic if you mix the theoretical gravity that you're illustrating with the actual gravity that's pulling down on the bowling ball. You could say the same for virtually any graphical representation, though.

I love einsteinian spatial concepts. Sometimes the math is heavy. Sometimes it is remarkably easy. I like the formula for time dialation and Lorenz/Fitzgerald contraction. "Elegant Universe" by Brian Greene is great book at illustrating this plus he uses everyday comparisons to make his point. Better than "Brief History of Time" by far. Also tackles quantum physics quite well too.

Astrophysics kicks ass, as does QM and cosmology. And eveybody's favorite General relativity.

m= mo/sqrt(1-(v/c)^2). Go mass increase.

That's the Lorentz transformation isn't it?

Never mind, I see what you meant. Yes, it's circular logic if you mix the theoretical gravity that you're illustrating with the actual gravity that's pulling down on the bowling ball. You could say the same for virtually any graphical representation, though.

for example?

p.s. I wasn't suggesting it wasn't a good way of illustrating it, I sure as heck can't think of a better one.

Gravity is fun. The force of attraction between all matter. Of corse the force is greater with larger masses and when the distance between the masses is smaller. It can be summarized in the formula:

F = G(m1)(m2)/r^2

where G, the universal gravitational constant is 6.67*(10^-11) N*m^2/kg^2.
m1 is the mass of the first object in question, and m2 the second, both measured in kg. And finally, r, being the distance between the two objects, or if you prefer, radius, measured in meters.

Newtonian approximation, good at very sublight speeds only.

For example: to paint a landscape, you need to transfer a three-dimensional image onto a (virtually) two-dimensional medium. To accomplish this representation, you have to apply layers of paint -so the representation of the three dimensional scenic image actually relies on three dimensional physics, although you are applying them in a (supposedly) two-dimensional way. IOW: You represent the 3D image by painting it in a 2D format. To appopriately paint the image, though, you need to use 3D methods(since we literally can't inhabit only one or two dimensions).

We just start nuclear physics in class today very very interesting all about how the sun makes all the different elements. already done some astro physics enjoyable but i found it pretty difficult.

I enjoy astrophysics and quantum physics and hopefully get to do more in school this year, I might manage to understand quantum physics properly :D .

I have on memorable moment in my Physics lecture... mind you it may be because it was the only time I ever payed attention, but that's another story kids.


Inertial reference frames... or as my lecturer like to call them... "Belly-button co-ordinates"


Incidentally, I got roped into being the secretary of the Physics club at my uni... oh dear... oh dearie dear...

Speaking of hamsters, if anyone goes to Adelaide Uni, join SPACED!! We have stuff! Good god, we have stuff!

I just failed to see the reason as to why my monkey is still alive

I did a third of my BSc in physics; I avoided all astrophysics like the plague (I only had to do a third of the course, so chose what areas I wanted) so can't really comment on how interesting it is.

Quantum mechanics is really interesting, until you start to do any of the useful stuff, then it just gets so hard it's silly.

I did fairly well in Quantum, but now that I've graduated I've never had to use any of it, I just do nuclear now.

I just failed to see the reason as to why my monkey is still alive


Was he wearing pants? Coz that'll do it...

I believe that a very esteemed scientist once said, "Nobody understands quantum mechanics."
Richard P Feynman.

I'm more into topology myself. I guess this means that I'll spend my life chipping teeth as I try to eat coffee mugs, or scalding my fingers trying to pour coffee into donuts. ;)
http://www.shef.ac.uk/nps/Wurble.html

Newtonian approximation, good at very sublight speeds only.
Good in weak gravitational fields only.

for example?

p.s. I wasn't suggesting it wasn't a good way of illustrating it, I sure as heck can't think of a better one.
In flat space the shortest distance between any 2 points is a straight line. Now think of a sphere. As anyone who's ever been in a plane knows the shortest line between any two points is a curve (a section of a "great circle" which is any circle that splits the sphere exactly in half like the equator or a line of longitude on the Earth).

Similarly, space-time is curved (really this is a 4d curvature but you can think in 3d to get the intuition right, nobody can think in 4d) and the path of any object will be along a "geodesic", which is whatever is the equivalent of a straight line or great circle in that geometry.

Imagine a light wave. If I emit a pulse from a point it moves outward at speed of light in a circle (like dropping a stone in a pond). In 3d space it is a circle moving outwards. In 4d space time it is a cone. (see http://www.theory.caltech.edu/people/patricia/causb.html x is the distance and ct is the time multiplied by the speed of light). Note in 4d nothing ever moves. Everything is stationary since time is just another coordinate on an axis). In curved space time it will not be a cone either, it will be a misshapen cone with curved edges.

Newtonian approximation, good at very sublight speeds only.

Yes, I know it's an approximation. I'm sorry if any top scientits used G as I defiened it to determine the gravitaional force between various large masses, such as the planets. If you did, you answer may be inaccurate.

Yes, I know it's an approximation. I'm sorry if any top scientits used G as I defiened it to determine the gravitaional force between various large masses, such as the planets. If you did, you answer may be inaccurate.

Was your G off? that wasn't my point...

Yes, I know it's an approximation. I'm sorry if any top scientits used G as I defiened it to determine the gravitaional force between various large masses, such as the planets. If you did, you answer may be inaccurate.

He is not talking about a constant to be an approximation, but he is talking about the theory itself being an approximation. He mentioned sublight speeds because when objects start moving at a speed 'comparable' with the speed of light, you have to use einstein's formula's.

yo all. I am hoping to study string theory/quantum sometime. Anyone here got a degree in strings?
Toasters can understand the universe too :)

Was your G off? that wasn't my point...

Is that formula just not the most accurate? I haven't taken AP Physics yet.
Ok, now I understand. Makes sense that it wouldn't work near the speed of light. My mistake.

Uhh, physics.

Well...I can calculate energy and stuff like that...

I stopped it in year 11...but I did like it.

The speed of light isn't the issue, that's special relativity. In GR it is the strength of the field that is important (you need GR for high speeds OR heavy objects.) You can't describe a black hole with Newtonian gravity even if it is stationary.

If black holes exist...

Does somebody know wheter the Gravitational Constant (G), as in the formula stated before in this thread, is now known to be NOT constant?
Just like the Light Speed (c) is now known to be not constant...
The 2 constants of the universe collapse: ain't it great... :p

If black holes exist...

Does somebody know wheter the Gravitational Constant (G), as in the formula stated before in this thread, is now known to be NOT constant?
Just like the Light Speed (c) is now known to be not constant...
The 2 constants of the universe collapse: ain't it great... :p

The speed of light is constant, if it is in a vacuum. It is slower when traveling through denser matter, such as water. In a vacuum it is 3*10^8 m/s.

Nope, It used to be faster than it is right now
The difference is small, but it is still there.
It has something to do with the space-time-density decreasing

Just like the universe in the beginning expanding faster than our current light speed, so particles would not have any effect on each other, but they did because the space-time-density was huge)

I got a B1 in Leaving Cert Physics. That's between 80% and 85%. :)

It wasn't very advanced stuff. We studied light, sound, heat capacity, Newtonian mechanics, a lot of electricity, electromagnetic radiation and particle physics.

Nope, It used to be faster than it is right now
The difference is small, but it is still there.
It has something to do with the space-time-density decreasing

I think I've heard something like that before. Must be because of the way the universe is expanding.

Nope, It used to be faster than it is right now
The difference is small, but it is still there.
It has something to do with the space-time-density decreasing
I'd heard that proposal before, but could swear it had been shot down, the same as "tired light" to explain high redshits.

Can you point me to a (reputable) source for the "speed of light in a vacuum is not a constant" thing?

I'd heard that proposal before, but could swear it had been shot down, the same as "tired light" to explain high redshits.

Can you point me to a (reputable) source for the "speed of light in a vacuum is not a constant" thing?
My physics teacher

EDIT: The space-time-density is being avoided by most physics profs because it's close to quantum physics (or is QP, I don't know) and no one really knows a lot about that for sure. It's all theory...

Erm. No insult to your teacher, but I was really hoping for a cite from a published paper or something similar. Given how easy it is to get mixed up / misunderstand / mis-communicate things in such a complicated field, just 2nd-hand word like that isn't going to convince me.

Do you suppose your teacher might be willing to provide a cite to the source?

The theory that the speed of light has changed is wildly speculative and is not widely believed, to put it mildly. This is different from the phenomenon of inflation which I assume others were referring to where the universe is supposed to have undergone extraordinarily rapid expansion for a period after the big bang and is regarded as a very plausible and respectable theory amongst cosmologists. As for "space-time density" I'm not even sure what you're talking about.

We also come to the fact of quantum tunneling where particles tunnel through space and reappear thereby in principle going faster than light.

If black holes exist...

Does somebody know wheter the Gravitational Constant (G), as in the formula stated before in this thread, is now known to be NOT constant?


It was hypothesised for a long time, but I believe it has now been disproven.
The fact is that GR has little or no evidence so there are many possabilities, it only has been assumed to be right because the calculations work.