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Geology, Palaeontology & Archaeology / Re: What causes Earth's magnetic field?

« on: 23/09/2018 11:22:06 »

There is a metallic flow but that won't produce a magnetic field, either.

The energy source is the heat released by the liquid outer core slowly solidifying, causing the solid inner core to slowly expand over time. This heat release causes convection currents in the liquid outer core.

The magnetic field itself is produced by electrical currents in the liquid nickel/iron, produced by magnetohydrodynamic effects.

In laboratory experiments, two additional factors are needed to kick-start the dynamo:
- Differential rotation of Earth's solid inner core and the mantle
- a "seed" magnetic field (that may have come from the solar magnetic field?)

These effects have been reproduced in the lab using a model with liquid sodium instead of liquid iron. One of the more recent experiments is described here:

the temperature is well over the Curie temperature so the iron and nickel are non-magnetic.

Sodium is not ferromagnetic, and yet the effects are reproducible in the laboratory because the metallic flow and electrical currents are similar (just faster).

The Sun also displays a magnetic field -  the Sun is composed mostly of a plasma of Hydrogen and Helium; these elements aren't ferromagnetic either.

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Physics, Astronomy & Cosmology / Re: Is it possible to slow light down?

« on: 21/11/2016 10:17:30 »

I heard it described nicely one - light slows down when going through some substances, but it's like a person walking through a busy room. The person walks at exactly the same speed, but goes from person to person, meaning it takes him longer to get through the room than if there was no-one there. Similarly, light doesn't get slower, but takes longer to get through some things.

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Physiology & Medicine / Re: How much protection do they eyelids provide?

« on: 10/10/2016 21:21:47 »

You can lie in direct sunlight with your eyes closed perfectly safely. You see a warm red color, which is due to the red blood cells in the capillaries of your eyelids.

But your iris also has a considerable SPF.
- In the dark it opens wide, and in bright sunlight it closes down small. This gives an order-of-magnitude variation in light intensity
- If you are looking in the sky somewhere near the Sun, your iris blocks a considerable amount of light from striking the retina (don't look straight at the Sun!)
- Slightly more if you are brown-eyed compared to blue-eyed

The cornea and lens of your eye block parts of the infra-red spectrum.

Be aware that UV damage to the eyes is cumulative, and increases the chance of cataracts.

The lens of the eye blocks UV light - it is said that people receiving glass lenses in early cataract surgery were able to see in UV light, as glass is less effective at blocking UV light. But I suspect that the UV light now reaching the retina would damage the retina.

In bright sunlight, wear sunglasses which have been tested to block UV light.

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General Science / Re: For relativity, does the mass of a moving object increase in all directions?

« on: 03/09/2016 22:38:28 »

What does this "does the mass of a moving object increase in all directions?" actually mean?

I have a mass of about 70Kg. It's not in any direction; it just is. Mass is not a vector quantity.

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Physics, Astronomy & Cosmology / Re: Gravity curves spacetime but that's because it stretches spacetime

« on: 15/07/2016 16:37:54 »

That Einstein used dubious metaphysics is not an argument for adopting dubious metaphysics.

And where,  pray tell, in this forum did I make such an argument? All I said is that there are physicists, including Einstein, who though of it that way. And it's far from being dubious in any way, shape of form whatsoever. And this isn't dubious anyway. Just because that's your opinion it doesn't mean that it reflects anybody else's opinion. Far from it in fact.

In any case what Einstein thought on points like this should never be dismissed or ignored. It was those kinds of thoughts which helped lead him to his general theory of relativity. Why do you think Einstein is quoted so often such as in articles which try to convince physicists to stop teaching relativistic mass. In nearly all of those articles they quote his statement against velocity dependent mass. However, little did they know he wasn't speaking of relativistic mass in general.

Next time (or at least until the ignore list function is working again) please make an effort for present a cogent argument of your beliefs rather than merely stating assertions such as "dubious metaphysics". Merely making assertions by stating your opinion helps nobody.

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Question of the Week / Re: QotW - 15.12.06 - Would polar bears thrive in Antarctica?

« on: 10/12/2015 03:09:52 »

Penguins have been relocated north ...

http://www.thefreelibrary.com/Humboldt+Penguins+%28Spheniscus+humboldti%29+in+the+Northern+Hemisphere.-a0165779778

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Physics, Astronomy & Cosmology / Re: Has Time Rate Underground Compared to at the Surface Been Measured?

« on: 18/07/2015 04:49:26 »

Has an experiment been done to verify that time runs faster below ground than at the surface?

There have been many tests of gravitational redshift that have been done above ground, and in satellites. Some of the equipment is small enough to be used down a mineshaft, but I can't see a description of these experiments being done.

I think the result will be the opposite of what you expect.

Time runs slower the further you go down a gravitational well (as measured by a distant observer). So the centre of the Earth is the farthest down the Earth's gravitational well as you can go, and I expect that time will run slowest there.