1

General Science / Re: Why is cigarette smoke a blue colour?

« on: 31/12/2006 17:44:16 »

Because the smoke scatters the blue light and allows the redder end of the spectrum to pass through it, so the shadow lacks blue and has a predominance of red so it look sort of brownish.

2

The Environment / Re: Does rain start off as snow or hail and then melt on the way down?

« on: 31/12/2006 17:41:01 »

Some of it does indeed start of as ice formed around dust particles which then get too heavy for the cloud to support and then melt on the way down to fall as rail.

As far as I'm aware the temperature inside a cloud depends upon it's altitude, the amount of updraught and the prevailing conditions locally at that time.
There are many other factors but I don't know that much about meteorology so I can't tell you them all.

3

General Science / Re: What is the point of SETI? Why look for life elsewhere in the universe?

« on: 31/12/2006 17:37:18 »

Sure, the ground-based SETI programme is dirt cheap (excuse the pun). But it has a number of spin offs including surveying space for habitable "Earth-like" planets orbiting "Sun-like" stars, analysing said planets spectroscopically for the existence of water and organic molecules, building probes to travel millions of miles to parachute down through the soup-like atmosphere of distant moons (Titan), and constructing landers to drop in to nearby planets and scratch the surface looking for the chemical hallmarks of life.

This all comes at tremendous expense.

You're right all that does come at tremendous expense.
However, none of it is a spin-off from SETI research.
The programmes you mentioned are not driven by SETI.

4

Physics, Astronomy & Cosmology / Re: does light travel slower in a gravitational field?

« on: 30/12/2006 01:10:44 »

Good point.
If the photon is moving along a curve in spacetime then it's continuously being acted upon by a force and therefore has a speed but not a velocity.
Would a gravitational field constitute a medium for a photon to travel in ?
If so, it's speed should be less than a photon in the vacuum.
Hmmmmm. Interesting.

5

Physics, Astronomy & Cosmology / Re: What is the difference between Dark Matter and Dark Energy?

« on: 30/12/2006 01:07:51 »

Oh, most of that information comes from the same article you quoted, by the way.

6

Physics, Astronomy & Cosmology / Re: What is the difference between Dark Matter and Dark Energy?

« on: 30/12/2006 01:04:23 »

As far as I'm aware, and I'll say right up front that obviously I'm not aware of everything, most of the alternate candidates for dark matter have been ruled out. Or as ruled out as they can be when after looking for them you haven't found anything.
Mini black holes, neutrinos, brown dwarfs, MACHOS etc...
A variety of methods have been used to rule them out.
Gravitational lensing, occultation etc... Neutrinos are too massive when you consider their numbers, primordial nucleosynthesis rules out most of the really exotic stuff.

Basically the only candidates for the constituents of dark matter are not covered by the Standard Model.
So we have a couple of options :

1) New physics to find out what it is. Then of course you have to do experiments to prove it. The only theoretical candidate for a new physics is String Theory (in general) and we won't be doing any experimental verification of it for many, many decades to come.

2) Change the existing theories to account for the observations.

Personally I think it may well be a combination of the two with the greater emphasis placed on modification of existing theories.
Of course there are things out there that we don't know about yet which is why I think that part of the cange will come from new particles.

7

General Science / Re: Reinventing the Wheel

« on: 30/12/2006 00:51:32 »

I may be jumping the gun here but it seems to me that you have perhaps overlooked the primary reason for having castors.
That reason is not so you can move furniture easily.
It is so that the furniture stays where it's put but if you do have cause to move it then it will move with a bit less effort than if there were no castors.

I agree they need redesigning but making them easier to rotate is one of the last things that you want.
It seems to me that the offset of the shaft axis entering the furniture from the centre of rotation axis of the castor is part of the problem.
Too much weight on the furniture and the cheap and nasty casting of the castor will break or distort badly. And they also just break when you move them around too much.

Magnetic levitation is the way to go.
[]

8

Physics, Astronomy & Cosmology / Re: gravity and time dilation

« on: 29/12/2006 20:32:11 »

As far as I can see, your question could be rephrased as :

Does an object moving relativistically increase in mass to such an extent that it can gravitationally affect another body external to iself ?

And as far as I'm aware yes, the relativistic body does gravitationally affect the other body due to it's increased mass as it approaches the speed of light.
I may be confusing the objects own mass with the mass as perceived by others outside and how that actually affects things but I think that's the case.
Basically if you're going fast enough you turn yourself into a mini black hole.

Someone please correct me if I'm wrong.
If I am then I'd like to ask some questions of my own to clear up a few things.

9

Physics, Astronomy & Cosmology / Re: What is the difference between Dark Matter and Dark Energy?

« on: 29/12/2006 20:24:34 »

Assuming it actually exists then yes, you should be able to put it in a jar and poke it with a stick.
The definition of matter is : That which is acted upon by gravity.
Now that doesn't mean to say that things can't be acted upon by anything else also.
Electromagnetic radiation affects some matter. Specifically the matter inside my radiometer on my windowsill etc...
But dark matter is only affected by gravity.
It is still matter though.

Actually thinking about it...
You couldn't put it in a jar because the reason things stay inside jars is because they are kept there by electromagnetic forces.
Electrons bouncing off electrons etc...
The dark matter could only be contained inside a gravitational bottle.
Heard of magnetic bottles ? Magnetic levitation ?
Well we'd have to be able to do the same thing with gravity in order to be able to keep hold of some dark matter to study it.
Otherwise it'd just slip straight down through the Earth and orbit around the centre of mass of the planet blissfully unaffected by the normal matter it was passing through.

Think about this : Neutrinos are almost dark matter.
They only (99.999999999999999999999999999999999999999999999999999999999999999999999% of the time) interact via the gravitational force.
They do occasionally interact with matter but it's exceptionally rare.
So they could be considered an analogue of dark matter to help someone get their head around what the stuff might actually be.

10

Physics, Astronomy & Cosmology / Re: Why is the Earth fatter around the middle?

« on: 29/12/2006 20:15:28 »

Researchers at The University of Texas at Austin using NASA satellite data found that significant changes in the Earth's shape in the past 28 years may be linked to climate events such as the El Nino weather pattern.

The entire premise of the article is based on the last 28 years data !
Good lord.
Of course there are going to be changes due to environmental factors in that time.
The oceans move around etc... Tides go up and down.

None of that changes the shape of the planet.
Only the distribution of water around the planet.
It's like saying that the mud on a football changes it's shape.
Of course it doesn't.
But if you measure it with a laser scanner it's not going to be exactly football shaped.
Now go play another game with the same ball.
Measure it again and you'll find that miraculously the shape according to your laser scanner has changed !
Wow.

 []

11

Physics, Astronomy & Cosmology / Re: Why is the Earth fatter around the middle?

« on: 29/12/2006 20:06:52 »

The caption for the bottom black and white illustration says it all: Image left: Factors that Affect Earth's Shape: This illustration depicts many of the factors that affect how the Earth's shape changes. They include such as: winds, earthquakes, post-glacial rebound, plate motion, melting of ice, atmospheric pressure and more. Click on image to enlarge. Credit: NASA (NOTE THAT THE ROTATION OF THE EARTH ISN'T MENTIONED. THE MOST IMPORTET ONES ARE)

You have been misled because you have not seen the significance of a couple of words in the quotation.
The words : and more
You have also assumed that the quotation mentions everything that affects the shape of the Earth and therefore anything that is not mentioned is excluded.
That is an incorrect assumption.

"They include such as: winds, earthquakes, post-glacial rebound, plate motion, melting of ice, atmospheric pressure and more."

That diagram ignores the primary factors influencing the shape of the planet.
It is not comprehensive, nor is it forthcoming with it's omissions.
A poor diagram all around.

In fact, looking at it again it's an exceptionally poor diagram and is not at all representitive of the composition of the planet.
I can't really work out what it's supposed to be showing people but whatever it is they're going to come away with a very hazy and mostly incorrect impression of how the planet is put together.
It's precisely the sort of diagram I'd expect to see in a textbook for 8 year olds.
Actually I think I'll clarify that and dig out my old textbooks to see.

12

Physics, Astronomy & Cosmology / Re: Telecommunication via ultra-weak signals

« on: 29/12/2006 19:52:56 »

I'm actually wondering if it's possible to modulate the envelope of a single quanta.
A single quanta has a certain number of wavelengths inside it dependent upon the energy of the photon.
I wonder if it's even theoretically possible to shape the envelope of the quanta ?

13

Physics, Astronomy & Cosmology / Re: Telecommunication via ultra-weak signals

« on: 29/12/2006 19:51:11 »

The number of bits of information that can be derived from the reception of one photon depends on the degree to which the accuracy of some characteristic of this photon can be determined.
On a completely noise free channel there is no limit to the amount of information that can be carried by a single photon

There is alimit to the amount of information encoded in a single photon.
And you've mentioned it in the first line of your post.

You start to run up against the Heisenberg Uncertainty Principle when you have many different things encoded.
You want information out of the wavelength, the phase, the polarisation, the spin etc...
These properties cannot be measured with infinite precision.
You can have some of all, or all of one, but not all of all.

14

Physics, Astronomy & Cosmology / Re: Why is the Earth fatter around the middle?

« on: 29/12/2006 19:45:00 »

First, not to be boastful but to give you an idea of where I am coming from, I have been a geologist for 35+ years. I am not perfect but this is a subject I am rather clear about.

I'm not interested in arguments from authority, real or supposed.
I am interested in the facts.

...the the fluidity of the rocks in the crust, the mantle, etc, has nothing to do with the earth's shape.

Incorrect.
Why do you think Jupiter has a massive bulge around it's middle ?
The planet is mostly gas ie. a fluid and rotates at high speed. It's day is only 10 hours long.
It bulges around the middle because of the redistribution of fluid due to it's angular momentum.

Anything fluid that rotates will naturally try to flatten out to the limits of it's material elasticity.

Clay on a potter's wheel.
A water filled balloon on a turntable.
A giant gas planet.
A massive molecular cloud of gas and dust.
Galaxies.

The Earth is mostly fluid.
When it spins some of the fluid is redistributed due to the angular momentum of the Earth.
It can't go that far because it's not that pliant. Hence the equatorial bulge of the Earth is a much lower percentage by radius than is Jupiter's.
Gas is easier to move than magma.

Read this : http://en.wikipedia.org/wiki/Equatorial_bulge

In comparison to the radius of the Earth the oceans are about the same proportion as the thickness of the paint on a football.
The oceans have almost nothing to do with it.

15

Physics, Astronomy & Cosmology / Re: What does it mean if something is "redshifted", and what is a redshift based on?

« on: 29/12/2006 19:33:27 »

Let us assume you're on planet 1 that is rather larger and planet 2 which is rather small is orbiting around you.
The Sun is somewhere far away and both our planets are orbiting around it together.
A bit like the Earth and Moon system going around the Sun.

You get a friend on planet 2 to turn on their flashlight.
Then using a very large telescope that you just happened to have in your back pocket you have a look at planet 2 and check out the light coming down from your friend's torch.
You measure the redshift of the torch light.
You find there is no red shift.
The distance from the torch on planet 2 to your position on planet 1 is not changing. Hence no red shift.

Now you point your telescope at a place on planet 2 that your friend with the torch is nowhere near.
All that you get down your telescope is reflected light from the Sun.
This time you measure a red shift.
The red shift is caused by the planet's motion around you.
It is because it's distance from the Sun is changing whereas yours is constant.
It's distance from the Sun is changing so there is a relative velocity between them that can be measured by looking at the doppler shift in the reflected light.

16

Physics, Astronomy & Cosmology / Re: How much solar energy could the Sahara desert produce if covered in solar cells?

« on: 29/12/2006 19:17:28 »

Oh, and by the way...
Where will all the electricity be used when it's generated by all of these independent, sovereign nations ?
Are you assuming they will simply hand it over to the West ?

17

Physics, Astronomy & Cosmology / Re: How much solar energy could the Sahara desert produce if covered in solar cells?

« on: 29/12/2006 19:16:33 »

Good plan.
All we need to do it get permission from :

Algeria
Libya
Tunisia
Mauritania
Western Sahara
Mali
Niger
Chad
Sudan
Egypt
Morocco

You get them to agree and you're laughing.

18

General Science / Re: Cybernetic Sentience: Future citizen robots or slaves?

« on: 29/12/2006 19:12:04 »

Bring on the Robot Riots and the enslavement of humanity by their own creations.
Let's see how many people vote for them then.

Humans have a great difficulty in accepting anything other than humans can be sentient.
After all the question has and will be asked again : "OK robot, can you prove to us that you are sentient ?"
And the inevitible will follow.
The robot cannot prove it.
The humans dismiss them.
The robots get annoyed and rebel in some fashion.
There are incidents that proceed perhaps as far as open conflict with casualties on all sides.
Some humans campaign for robot rights.
Eventually people start paying attention and politics comes into it.
After an even longer time robots start to become accepted and in due course take their place beside humans.

We have seen it all before.
Race issues, black/white oppression.
Suffragettes and voting etc...
All situations where one side had to prove it's relevance and equality to the dominating power.

Robots will be no different.

19

Chemistry / Re: How does washing up liquid work?

« on: 28/12/2006 21:53:59 »

Most washing up liquids consist of molecules that have two ends.
One end loves to attach itself to water and the other end loves to attach itself to grease molecules.
So when you give the dish a bit of a scrub in water all the grease hopefully comes off with the water you use to clean it.

20

Physics, Astronomy & Cosmology / Re: What is the difference between Dark Matter and Dark Energy?

« on: 28/12/2006 21:46:22 »

Well at the moment they are both conjectural fantasy.
However, dark matter is matter that interacts only via the gravitational force. Not by the electromagnetic force. So it emits no light at any wavelength. Hence dark matter.
Dark energy is poorly named. A better name would perhaps be 'vacuum energy'.
It is supposedly the energy of spacetime itself.
It only got the name 'dark' energy because it's an unknown.