Ask a physicist anything. (3)

[pgp_protector]

Google sky... I have it on my mobile and I geek out everytime I use it.

Yea,but I need to do it offline (and on a Microprocessor )

(Also has Google Sky & loving it on my GalaxyS )

 

[Nabobalis]

Well sure, that's the nuance of the question I wanted to incite heated and vitriol debate on just what constitutes the boundary of an atom. That said, what did you use for the atomic radii?

I use what ever the question asks of me . Never used it otherwise than exams and shell models and the like.

 

[Wiccan_Child]

I use what ever the question asks of me . Never used it otherwise than exams and shell models and the like.

No no, in your answer, you said:

"Atomic radius 156 pm
Covalent radius 196±7 pm
Van der Waals radius 186 pm"

What did you use for the first value? Where did 156pm come from?

 

[dewaddict84]

Here's a question: If time slows down as you approach the speed of light, and light travels AT light speed, does that mean that light experiences no time between being generated and hitting whatever it hits?

Or am I getting something wrong?

 

[Wiccan_Child]

Here's a question: If time slows down as you approach the speed of light, and light travels AT light speed, does that mean that light experiences no time between being generated and hitting whatever it hits?

Or am I getting something wrong?

Pretty much. Light sees the universe as being static and 2D. But most physicists agree that Quantum Mechanics trumps General Relativity in cases where they disagree, so GR is, ultimately, wrong. I personally think that what like 'sees' is one of the things that GR gets wrong; it's broadly right, but, like classical mechanics, it gets small details wrong.

 

[Chesterton]

Pretty much. Light sees the universe as being static and 2D.

Why 2D?

 

[Wiccan_Child]

Why 2D?

Because when you look at a moving object, it's shorter than when it's stationary. As it approaches lightspeed, it looks shorter and shorter. When it's at lightspeed, it has no length. Thus, it goes from having length in three dimensions to only having length in two dimensions. Since the photon would see the entire universe moving along at lightspeed, it sees the entire universe as being 2D.

But like I said, this is probably just a niggle that GR gets wrong.

 

[Chesterton]

Because when you look at a moving object, it's shorter than when it's stationary. As it approaches lightspeed, it looks shorter and shorter. When it's at lightspeed, it has no length. Thus, it goes from having length in three dimensions to only having length in two dimensions. Since the photon would see the entire universe moving along at lightspeed, it sees the entire universe as being 2D.

But like I said, this is probably just a niggle that GR gets wrong.

Does a moving object approaching lightspeed only contract relative to the direction it's moving? Or would it get less tall and less wide, as well as less long?

 

[Wiccan_Child]

Does a moving object approaching lightspeed only contract relative to the direction it's moving? Or would it get less tall and less wide, as well as less long?

Only in the direction it's moving. A spaceship moving forward would have its fore and stern sections come closer together, while a spaceship moving sideways would have its port and starboard sections come closer together. In general, an objection contracts along is direction of movement, like you said.

 

[Chesterton]

Only in the direction it's moving. A spaceship moving forward would have its fore and stern sections come closer together, while a spaceship moving sideways would have its port and starboard sections come closer together. In general, an objection contracts along is direction of movement, like you said.

What explains that? The port and starboard sides of a spaceship moving forward at lightspeed would be moving at the same speed as the fore and stern sections. So why wouldn't light perceive the universe as a point of no dimension, rather than perceiving two dimensions?

 

[Wiccan_Child]

What explains that? The port and starboard sides of a spaceship moving forward at lightspeed would be moving at the same speed as the fore and stern sections. So why wouldn't light perceive the universe as a point of no dimension, rather than perceiving two dimensions?

For the same reason that compressing an accordion only compresses it along one axis - even though the entire thing, port, starboard, fore, stern, is moving. It compresses laterally, along one axis. It doesn't compress left-to-right, because it's not moving left-to-right. It compresses front-to-back, because it's moving forward.

 

[catzrfluffy]

What does the Sun orbit?

(I may have asked this before. )

 

[Cabal]

What does the Sun orbit?

(I may have asked this before. )

The common centre of mass of the solar system.

 

[catzrfluffy]

Cheers.

So it isn't slowly orbiting another star?

 

[Cabal]

Cheers.

So it isn't slowly orbiting another star?

Eh, our solar system is whirling around in one arm of our galaxy, but I don't believe we're in a binary system. I don't see why there couldn't be some very weak, long-range interaction with another body, gravity is an infinitely-ranged force, and there's a lot of matter in the universe, but I don't think there's compelling evidence for any. What I could find on it seemed to bear the hallmarks of crackpottery.

 

[alexacker]

What does the Sun orbit?

I think the supermassive black hole in the centre of our galaxy

 

[pgp_protector]

I think the supermassive black hole in the centre of our galaxy

and what does our galaxy orbit?

 

[Nabobalis]

and what does our galaxy orbit?

It isn't I think. It will crash head first into andromeda galaxy some day. But It could be the c.o.m of the local cluster?

 

[Wiccan_Child]

It isn't I think. It will crash head first into andromeda galaxy some day. But It could be the c.o.m of the local cluster?

I think the whole Local Cluster is moving towards a region of space called the Great Attractor. This is pulling things from my deep memory, mind, so I could be quite wrong

 

[Nabobalis]

I think the whole Local Cluster is moving towards a region of space called the Great Attractor. This is pulling things from my deep memory, mind, so I could be quite wrong

Well a quick wiki search makes no mention of that.

I might do a search of the literature if the flu doesn't get the best of me.