Ask a physicist anything. (3)

[dewaddict84]

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,

Well cut it out! Your deep memory is pulling us right into this Andromeda character and we're going to crash!

and pft, don't you think that's a little vain? I mean, sure, you're young, but you really think you're that attractive?

 

[catzrfluffy]

...And the Universe is solved!!!

 

[Wiccan_Child]

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.

The Great Attractor is real, and although Wiki doesn't state it outright, other sources confirm that we are indeed moving towards it. It's located near Leo and Virgo, so that part of the sky might as well be the 'front' - though it's located in the zone of avoidance (the band of sky dominated by the milky way), so the galaxy is moving towards the Great Attractor side-on. Essentially a big Frisbee moving at 700 mph...

 

[Wiccan_Child]

Well cut it out! Your deep memory is pulling us right into this Andromeda character and we're going to crash!

and pft, don't you think that's a little vain? I mean, sure, you're young, but you really think you're that attractive?

The only attractive people are young people! Everyone circulates around me baby

 

[KIYX]

the Great Attractor

That was my nickname in high school.

HAH.

I wish.

 

[KIYX]

Hmm, here's something I've always wondered, given that there was a "big bang" why aren't all the galaxies moving away from that center point? Why are some of them colliding?

 

[Chesterton]

Hmm, here's something I've always wondered, given that there was a "big bang" why aren't all the galaxies moving away from that center point? Why are some of them colliding?

Because gravity is a weak force. It will cause close things, like two close galaxies, to attract each other if they are already close, but it's not strong enough over great distances to attract distant things. Kind of like magnetism. If you hold a refrigerator magnet an inch away from the fridge, they will attract each other. If you hold the magnet six feet away from the fridge, you get no attraction (or at least no attraction strong enough to be detectible by human mechanisms).

Is that right, Mr. Physicist?

 

[Wiccan_Child]

Hmm, here's something I've always wondered, given that there was a "big bang" why aren't all the galaxies moving away from that center point? Why are some of them colliding?

Because there was no 'centre point'. The Big Bang refers to an expansion of space. It's not that all matter and energy exploded out of a point somewhere in space - rather, space itself has been expanding for about 13.5 billion years. Space contains matter and energy and all that jazz, and the expanding universe affects that. For example, early on, the universe was tiny, so everything was squished, making it very hot and dense. Nowadays, the average temperature is about 2.6°C above absolute zero.

Anyway, Chesterton's right, gravity is pretty weak; while things are, by and large, moving outward (every galaxy sees every other galaxy moving away from it), there are exceptions: gravity can be strong enough to overcome the expansion of space. This is evident with the Andromeda galaxy, but also when I drop an apple. Both are ostensibly the same thing.

 

[Gracchus]

I have been reading Hawking's new book, and a question occurred to me. In the experiment which photons (or buckyballs) show diffraction patterns by apparently passing through both slits in the screen, what happens if the slits are not parallel? What happens if you vary the distance between them? In fact what happens if one slit is rotated with respect to the other? What happens if there are more than two slits?

If a photon passes through two or more black holes into a single universe on the other side... Naw, just stick with the first questions for now.

 

[Cabal]

I have been reading Hawking's new book, and a question occurred to me. In the experiment which photons (or buckyballs) show diffraction patterns by apparently passing through both slits in the screen, what happens if the slits are not parallel? What happens if you vary the distance between them?

The distance between slits in a diffraction experiment will affect where the interference maxima are.

(order number*wavelength = slit separation*order angle)

Double-slit experiment - Wikipedia, the free encyclopedia

In fact what happens if one slit is rotated with respect to the other?

Well, the length of the slit is much bigger than the wavelength of the substance being diffracted, so that won't really affect things until you really start rotating it. As to what happens in a double-slit experiment when the slits are different size, I have no idea, but I should try and calculate it if possible...

What happens if there are more than two slits?

I know I've done the maths for this....will get back to you.

If a photon passes through two or more black holes into a single universe on the other side... Naw, just stick with the first questions for now.

My copy of Grand Design needs to hurry the heck up. Is it a good read?

 

[Nabobalis]

The Great Attractor is real, and although Wiki doesn't state it outright, other sources confirm that we are indeed moving towards it. It's located near Leo and Virgo, so that part of the sky might as well be the 'front' - though it's located in the zone of avoidance (the band of sky dominated by the milky way), so the galaxy is moving towards the Great Attractor side-on. Essentially a big Frisbee moving at 700 mph...

I wonder if that's Zeus. I got to admit, Greek gods are amazing. Why can't that have been the major religion?

That is a really interesting read tho. I really need to screw this obsession with particle physics and become an astronomer.

 

[Chesterton]

What is the softest substance known to man?

 

[Cabal]

What is the softest substance known to man?

Define "soft".

Gases are pretty soft, although I suspect that's the idea

 

[Chesterton]

Define "soft".

That's your job.

 

[Cabal]

That's your job.

OK

First thing that came to mind was the Mohs mineral hardness scale - talc is the softest mineral.

If I'm being pedantic, the weakest-interacting substance I can think off is matter that only undergoes the appropriately-named weak interaction, so neutrinos would be a good case.

Weakest atomic interaction would be some kind of degenerate bosonic state like a Bose-Einstein condensate.

 

[Wiccan_Child]

What is the softest substance known to man?

Dark matter.

 

[Assyrian]

Dark matter.

I thought when the were searching for dark matter they found it really hard?

 

[Gracchus]

What is the softest substance known to man?

The brain of a creationist?

 

[Nabobalis]

I thought when the were searching for dark matter they found it really hard?

That is what she said.

 

[Wiccan_Child]

I thought when the were searching for dark matter they found it really hard?

I'd be surprised if they discovered it was particularly hard - thus far, we only know it exists because of its mass, and that doesn't tell us much about its hardness. I said Dark Matter was the softest known to man because normal matter completely ignores it - even light can shine right through it. Might be stretching the definition of 'hard' though

That is what she said.