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The dumb questions thread

 
 
 
Kharakov said:
spikepipsqueak said:
I Can't find the dumb questions thread. Has no-one felt the need since we've been here?

Please merge, if I've just been slack.

There is a woman who repeats everything I say, with a delay of about half a second. She does it every time we meet, but she doesn't do it to anyone else.

I am a little pissed and the word "echolalia" keeps running through my head, but I don't think that is what this is.

Can anyone explain this phenomenon?
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You subconsciously remind her of her older brother, who she used to do this to while they were children. It's called "annoying your older sibling does stick your face that way syndrome", which is named after a similar behavior siblings engage in.

Or you could be losing it. Delusions of grandeur on a really small scale "this woman Tommy Two Times me and nobody else!"
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NobleSavage said:
Thanks for starting the thread spikepipsquek. I have no answer to your question. Can you give more details about the woman? The fact that she only does it to you is the strange part. Is there any evidence that there is something wrong with her? Are you sure she is not just making fun of you?


On, to my dumb question: With all our bad ass telescopes would be be able to detect a Dyson sphere if we were looking for one?
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http://home.fnal.gov/~carrigan/infrared_astronomy/Other_searches.htm

Or... watch this. Hey, is it cheating to google an answer, because it interferes with conversation?

[YOUTUBE]http://www.youtube.com/watch?feature=player_embedded&v=HwcLEwAshr4[/YOUTUBE]
 
I'm posting this in "The Dumb Questions thread" not the "Really Dumb Questions" thread because I think it is dumb, but not really dumb. :)

This is what I've picked up here and there: Stars are formed from gas and dust. Stars are made of hydrogen. Because of gravity there is nuclear fission. All the heaver elements are produced from stars. Do I have this right?

What is the "gas and dust"? After the big bang was it all hydrogen before stars?
 
Yes, mostly hydrogen and helium with trace amounts of lithium.

 Big_Bang_nucleosynthesis

To make heavier elements than that, we need pressure and time. In the early universe, pressure was abundant, but there wasn't enough time yet.
 
James Brown is correct. I would add that heavier elements are made in stars. That is up to iron. Heavier elements than iron are made when the star explodes. It sends atoms at very high speed into space which contain other atoms. These collide and produce heavier elements just like particle accelerators. These atoms then produce more stars and the process is repeated.
 
If you shot a cannonball into space at 10,000 mph would it ever hit anything or is the probability in favour of it continuing its journey unperturbed forever?

I need to stop drinking.
 
horseyhorsey said:
If you shot a cannonball into space at 10,000 mph would it ever hit anything or is the probability in favour of it continuing its journey unperturbed forever?

I need to stop drinking.
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If the cannonball is shot from the surface of the Earth at 10,000 MPH (with respect to the Earth), it will hit the Earth.

Escape velocity is approx. 25,000 MPH.
 
horseyhorsey said:
Damn, had a feeling that wouldn't be fast enough. So, let's say 'at escape velocity' then.
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Solar escape velocity is about 525km/s, so at a velocity lower than that (relative to the sun), an object will almost certainly hit the sun eventually - although as we see with comets, there is a very small chance of hitting Jupiter, a even smaller chance of hitting another planet, and a good chance of settling into a fairly stable orbit and hitting nothing for possibly thousands of millions of years.

Perhaps a better question is to ask how far an object with no rest-mass, such as a photon emitted from the Sun in a random direction, is likely to travel before it hits something.

The answer to that is 'a long way' - the chances that the photon will hit something within the lifespan of the universe is close to zero. A crude estimate of how much of the sky contains objects to be hit can be had by looking at how much of the night sky is black. Even taking account of the fact that looking at a patch of apparently empty sky in sufficient detail shows hundreds of galaxies at great distances, at every scale from the naked-eye view to the Hubble deep-field images, the night sky (or the sky viewed from outside the majority of the atmosphere) is mostly black; and most of the regular matter in the universe is in stars that are emitting light. So we can conclude that most randomly directed photons leaving the solar system will not hit a star; and non-stellar 'ordinary' matter (dust, black holes, planets etc.) amounts to close enough to zero* compared to stellar matter that excluding it from the estimate makes no significant difference.

'Dark matter' is another thing entirely; but as it appears not to interact with photons, it won't change the result either.

Given an infinite, non-expanding universe, the answer would be that the photon would always hit a star eventually; The fact that the night sky is not uniformly as bright as the surface of a star therefore shows that the universe cannot be static and eternal. see Olber's Paradox.



*Taking our Solar System as an example, the Sun contains around 99.8% of the total mass of the solar system; 0.2% of the mass is in planets, moons, dust, asteroids, comets, etc., and more than a third of that 0.2% is Jupiter.
 
Every small volume of "empty" space constantly has neutrinos and photons passing through it (relic radiation from the BB, stuff from distant stars, etc.). All of these particles have mass/energy that creates minute gravitational wells.

At what distance from a galaxy is the average number of photons and neutrinos traveling from the direction of the galaxy matched by the average number of photons and neutrinos coming from all other directions?

In other words, at some average distance from a galaxy (the thick greenish circle), the number of photons and neutrinos emitted from the galaxy (green arrows) will be of approximately the same intensity as the amount of photons and neutrinos (purple arrows) coming from ALL other directions:
m81m82_gendler_big.jpg
 
bilby said:
horseyhorsey said:
Damn, had a feeling that wouldn't be fast enough. So, let's say 'at escape velocity' then.
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Solar escape velocity is about 525km/s, so at a velocity lower than that (relative to the sun), an object will almost certainly hit the sun eventually - although as we see with comets, there is a very small chance of hitting Jupiter, a even smaller chance of hitting another planet, and a good chance of settling into a fairly stable orbit and hitting nothing for possibly thousands of millions of years.
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Assuming hh meant an object launched into space from Earth, that's nowhere near. You'd have to be practically at the surface of the sun to have that high an escape velocity. The rule of thumb for escape velocity is that any object in orbit is half way to the end of the universe. So, back of the envelope, the length of Earth's orbit is 150 million km times 2 pi, or about 1 billion km. Divide by 31 million seconds in a year, and that says the earth is going around the sun at 31 km/s. It has half of the required escape energy, and energy is 1/2 m v2, so you multiply the orbital speed by the square root of 2 (about 1.4), which gives 43 km/s as the solar escape velocity.

Given an infinite, non-expanding universe, the answer would be that the photon would always hit a star eventually; The fact that the night sky is not uniformly as bright as the surface of a star therefore shows that the universe cannot be static and eternal. see Olber's Paradox.
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That doesn't follow. Stars are grouped into galaxies. Galaxies are grouped into clusters. Clusters are grouped into superclusters. If that sort of hierarchical grouping goes on, on ever larger scales, forever, then you could have a static eternal infinite universe with a dark sky, because the farther a photon goes the less likely it is to hit anything.
 
Bomb#20 said:
Given an infinite, non-expanding universe, the answer would be that the photon would always hit a star eventually; The fact that the night sky is not uniformly as bright as the surface of a star therefore shows that the universe cannot be static and eternal. see Olber's Paradox.
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That doesn't follow. Stars are grouped into galaxies. Galaxies are grouped into clusters. Clusters are grouped into superclusters. If that sort of hierarchical grouping goes on, on ever larger scales, forever, then you could have a static eternal infinite universe with a dark sky, because the farther a photon goes the less likely it is to hit anything.
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Imagine space divided into concentric layers, like an onion. Layer 2 is (on average) twice as far away as layer one, layer 3 is three times as far, etc.

So a star in layer 2 will give 1/4 as much light as a star in layer 1. But, there is four times the volume in layer 2, so (assuming random distribution) we can expect four times as many stars.

Layer 3 has 1/9th as much light per star, but nine times as many stars.

Each layer, then, should provide the same amount of light to the earth. If there are infinite layers, then there will be infinite light. The whole sky will be white.

The only way your mega-structures could keep that from happening is if they somehow lined up the stars so that they were behind each other, with the nearer ones shielding us from the light of those farther away.
 
bilby said:
Perhaps a better question is to ask how far an object with no rest-mass, such as a photon emitted from the Sun in a random direction, is likely to travel before it hits something.
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This is highly dependent on that photon's wavelength.
 
Wiploc said:
Bomb#20 said:
That doesn't follow. Stars are grouped into galaxies. Galaxies are grouped into clusters. Clusters are grouped into superclusters. If that sort of hierarchical grouping goes on, on ever larger scales, forever, then you could have a static eternal infinite universe with a dark sky, because the farther a photon goes the less likely it is to hit anything.
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Imagine space divided into concentric layers, like an onion. Layer 2 is (on average) twice as far away as layer one, layer 3 is three times as far, etc.

So a star in layer 2 will give 1/4 as much light as a star in layer 1. But, there is four times the volume in layer 2, so (assuming random distribution) we can expect four times as many stars.
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You're not just assuming random distribution; you're assuming random distribution with equal probability in equal volumes of space. An infinitely deep hierarchy of clustering means the probability of a star per cubic light-year goes down and down the farther you go from any given star. There aren't four times as many stars in the onion layer twice as far away.
 
2 new, and 1 old dumb question.

new 1) Wouldn't a black hole singularity be a torus (mmmmhhh, forbidden donut) instead of a dimensionless point because of angular momentum conservation?


I would think that it wouldn't be flat, like a Kerr metric singularity because there would be a slight bit of angular momentum around the ring (over the donut through the donuthole).



old 2) I still want to know where the radiation/particle pressure from a galaxy matches that of intergalactic space (post #133 above).


Ha! I remember the other question I wanted to ask:

new 3) Does vibration effect superconductivity?
 
Kharakov said:
2 new, and 1 old dumb question.

new 1) Wouldn't a black hole singularity be a torus (mmmmhhh, forbidden donut) instead of a dimensionless point because of angular momentum conservation?


I would think that it wouldn't be flat, like a Kerr metric singularity because there would be a slight bit of angular momentum around the ring (over the donut through the donuthole).

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Not according to what I've read. It's counterintuitive, but there's no rule against a point particle having angular momentum. Electrons manage it, as far as we can tell.

old 2) I still want to know where the radiation/particle pressure from a galaxy matches that of intergalactic space (post #133 above).
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And now that we've established intuition is unreliable ...

...can't do the calculation; but intuitively, since radiation falls off according to an inverse square law, the high-order term in the radiation pressure from the rest of the universe will be whatever comes from the nearest big source. So if you head out of the Milky Way toward Andromeda, you can expect to reach the point where half your light comes from the Milky Way and half from everything else just a little before the point where Andromeda is just as bright as the Milky Way, i.e. when you're almost half way there. Of course in other directions it will be a lot further since there's no nearby Andromeda in most directions. To get an average you'd have to get a 3-D map showing all the galaxies out to fifty million light years or so, construct a 3-D Voronoi diagram, and measure the volume of the local cell.

Ha! I remember the other question I wanted to ask:

new 3) Does vibration effect superconductivity?
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Haven't a clue.
 
The questions in here aren't sufficiently dumb. Here's how it's done:

If the universe initially expanded quite evenly, is there some vague central point we could be focussing on to learn more about the big bang? Do we have any idea where that relative point is now, given how long the light from objects in its vicinity takes to reach us?
 
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