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General Science / Re: Why are there 360 degrees in a circle?

« on: 10/08/2012 20:06:01 »

It's really pretty obvious.

The ancients understood that the circumference of a circle is three times its diameter (realize that they only had bits of string to make the measurements, so they were not that far off.) They were really more concerned with dividing up right angles (North versus West etc) so, understanding the importance of the three thing, they chopped the right angle into three bits, then chopped each of those into three bits. As they had ten fingers, they divided each of the smaller divisions into ten bits.

3x3x10=90

The rest is history.

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Just Chat! / Will my septic tank explode if I put dog poop down the toilet?

« on: 10/08/2012 04:14:06 »

Our puppy had an accident at our friend's house. I was going to flush the evidence down the toilet, but he insisted it went in the trash can (dustbin). Does he know something I don't know?

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Physics, Astronomy & Cosmology / Re: What is the Xeno motion paradox?

« on: 10/08/2012 03:08:58 »

Due to the reality that exists, isn't the paradox then as stated, just a mathemtical exercise, admittedly or obviously not taking into consideration any actuality or reality?
 

There are various versions of the paradox and there is no definitive Zeno version. That was lost to antiquity. As David is using it to claim that Calculus is somehow defective and that space is granular, I think it's important that he specifies his particular version of it.

However, the version I'm aware says something like "at an instant in time, an arrow.........." The counterargument is, because time flows, there are no "instants in time", and if you use instants of time you have just assumed that time is granular which will lead to the inevitable conclusion that space is also granular.

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Physics, Astronomy & Cosmology / Re: What is the Xeno motion paradox?

« on: 10/08/2012 00:13:13 »

David,

I think you better set down precisely the version of the paradox that you are referring to so that we can test the logic to see if it even is a paradox, and, unless you have certain mystical powers, it might be best if you stop claiming that you know what Zeno was thinking.

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Physics, Astronomy & Cosmology / Re: What is the Xeno motion paradox?

« on: 09/08/2012 06:15:20 »

Zeno was fully aware that you could increase the number of steps without limit and that the step size would decrease proportionally without limit, but he was also able to see that it did not resolve his paradox. You either have to stop at some point and accept that the universe is granular or you have to take it all the way to the point where an infinity is introduced, at which point the maths breaks down. Zeno's paradox tells us that the universe is granular.

Yes, and the time interval also decreases proportionally without limit. You will end up with an arbitrarily large number divided by the same arbitrarily large number, which, if I'm not mistaken, is equal to one. Doesn't strike me as strong evidence that the Universe is granular.

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Physics, Astronomy & Cosmology / Re: What is the Xeno motion paradox?

« on: 09/08/2012 05:29:48 »

which in the case of Zeno's arrow paradox we can,

I don't think we can. The logic in the version of the Paradox of the Arrow that I know is faulty, so it's not really a paradox at all. I would not be too surprised to learn that Zeno understood that and decided to pull a fast one on us.

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General Science / Re: Why do LED tail lights trail to me and not to the rest of my family?

« on: 09/08/2012 00:50:18 »

To control the brightness of an LED the most efficient way is to pulse it ...

Gosh! Is there an echo in here?

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General Science / Re: Why do LED tail lights trail to me and not to the rest of my family?

« on: 09/08/2012 00:10:28 »

Ah ha!
 
"The IC delivers a 200Hz drive signal to the LEDs, with duty cycle adjusted according to the voltage level at DIM"
 
http://www.maxim-ic.com/app-notes/index.mvp/id/4316
 
Some people can probably detect 200Hz with their peripheral vision.

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General Science / Re: Why do LED tail lights trail to me and not to the rest of my family?

« on: 08/08/2012 23:57:33 »

Of course, it could simply be the mechanism they are using to control the power. LEDs are diodes (doh!) and they have a low forward voltage (around a couple of volts) that only varies slightly with current, so they require some sort of current limiting device. The simplest way to do that is with a series resistor, but that's very inefficient if they are being driven from 12 volts.

They might be using some sort of switching regulator to drop the voltage and limit the current while operating in tail light mode. The cheapest way to control the power efficiently is simply to turn the LEDs off and on with a particular duty cycle. It may be that they need to up the frequency a bit.

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General Science / Re: Why do LED tail lights trail to me and not to the rest of my family?

« on: 08/08/2012 23:03:08 »

It does sound as if they are turning on and off. The clue is that you notice it with your peripheral vision which has a faster response than your central vision.

My hunch is that they are deliberately maximizing the apparent brightness by driving the leds with short duration, high current, pulses. The eye is more of a peak detector than an integrator, so, for a particular average power, the LEDs will appear brighter when pulsed than when driven with DC. You can't do the same trick with incandescent bulbs because they have a lot of thermal inertia. LEDs can turn off and on relatively quickly.

If that is what they are doing, it's a bit naughty. Some people are very sensitive to strobed light. In my case it can even trigger a migraine attack.

I have noticed that the LED lights on Cadillac SUVs are particularly annoying. I thought it was just because they turn on so quickly, but maybe I'm detecting the strobe without realizing it.

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Physics, Astronomy & Cosmology / Re: Can the speed of light vary?

« on: 06/08/2012 22:33:55 »

The speed of light in a vacuum is derived from the permittivity and permeability of free space. It is reasonable to assume......

It's also reasonable to assume that it would not make the slightest difference.

The point is that the speed of light is not used as the definition of time as was tangentially proposed.

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General Science / Re: Is there a "potential energy" radio?

« on: 06/08/2012 21:28:58 »

It's perfectly possible to receive an FM signal on an AM radio. You just detune it slightly. The official name for this is "slope detection"

Yes, but I doubt if the detected signal will drive earphones without some some amplification. Anybody still got a crystal set?

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Physics, Astronomy & Cosmology / Re: Can the speed of light vary?

« on: 06/08/2012 05:03:13 »

My only point is that an atomic clock is just that - it's actually an oscillator that is locked to the atomic transitions of stimulated atoms, and the current definition of time is based on that technique. The adjustment process maximizes photon production, and that's the only connection there is with light, and it has nothing to do with the speed of light. I think there is a lot of confusion on this subject because most of the atomic clock descriptions I've seen don't do a very good job of explaining how they actually work!

There may be some interesting connection between c and atomic activity of course, but if there is, that's a different thing entirely.

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Physics, Astronomy & Cosmology / Re: Can the speed of light vary?

« on: 06/08/2012 01:05:33 »

But the atomic clock tunes the frequency of a microwave source to maximize the number of photons produced, so it's really only recovering the natural frequency of the atomic transitions. If c varied, why would it have any effect on the frequency of the atomic transitions?

BTW - I think we beat this to death at least once before

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Physics, Astronomy & Cosmology / Re: Can the speed of light vary?

« on: 05/08/2012 23:26:23 »

The SI definition of the second also depends on the electromagnetic force, being measured by the frequency of a transition in caesium 133. http://en.wikipedia.org/wiki/Caesium_standard

If something changed the velocity of light (electromagnetic radiation) in a vacuum, then it may potentially also modify this definition of time.

Are you sure about that? Caesium clocks don't care about the velocity of light.

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Physics, Astronomy & Cosmology / Re: Can the speed of light vary?

« on: 05/08/2012 18:59:07 »

However, the meter is based on the speed of light in vacuum.

Well yes. If time was also a function of c, you'd be pretty much up the creek.

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Physics, Astronomy & Cosmology / Re: Can the speed of light vary?

« on: 05/08/2012 18:13:44 »

In fact, this is so stable that it is now used as the definition of time

That seems to be a common misconception. The definition of time is not based on the speed of light. It's based on atomic activity.

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Physics, Astronomy & Cosmology / Re: Why Qm wants to act atoms exact the opposite all the time?

« on: 02/08/2012 06:22:46 »

All seems pretty straightforward to me

Obviously, the entanglement has created a sort of super-particle. Even when you split it apart, it is still a super-particle.

This is a good way to think of it, Geezer.  In classical mechanics, we can always think of 2 particles as 2 separate particles that, if they interact, do so by forces.  In QM, entangled particles are actually 1 quantum state.  You can't separate them into 2 particles interacting via some force--somehow they are one "superparticle." 

I suppose why I'm saying you can remove the "magic" is that if you start from QM and accept that things like entanglement are part of nature, what becomes interesting is how these effects vanish as you go to large-scale (classical) objects.  A lot of confusion comes from starting with classical mechanics and trying to make sense of entanglement in terms of classical ideas--especially since it has no counterpart there.

I'm probably missing something here, but isn't this a very powerful argument to support the existence of other dimensions - as in String Theory? Are the famous double-slit photon experiments another indication?

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Physiology & Medicine / Re: Is dry walling bad for your health?

« on: 01/08/2012 18:32:37 »

There were a lot of problems in the US recently caused by inferior imported drywall that contained a lot of power station fly-ash. This led to a lot of corrosion of electrical fittings and plumbing. In some cases the houses had to be completely gutted and rebuilt. I imagine this could cause some health issues too, but whether this has anything to do with your situation I do not know.

If I remember correctly, the houses in the US that had the problem were mainly in areas with high humidity. A lot of people noticed a "rotten egg" smell, which suggests the presence of poisonous hydrogen sulphide gas.

EDIT:

I found this link http://en.wikipedia.org/wiki/Chinese_drywall

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Physics, Astronomy & Cosmology / Re: Is the trampoline analogy for the bending of spacetime inaccurate?

« on: 01/08/2012 03:53:53 »

Neither diagram is very accurate.  Space-time is 4 dimensional, and those pictures are 2D and 3D, not 4D!  I guess the 3D one is one dimension "closer," though that doesn't make it accurate.

Not sure I would discount it that much. The Earth orbits the Sun in a plane that is pretty much two dimensional (three including time), so the rubber sheet analogy works fairly well. My brother had to have rubber sheet too, but this might not be the best place to discuss that.