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Physics, Astronomy & Cosmology / How accurate are dating methods?

« on: 17/06/2011 17:39:48 »

I once read about rocks that were dated to 3.2 billion years by five different methods with perfect agreement, allowing for the small uncertainties in each.

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Physics, Astronomy & Cosmology / Re: What would we see at the edge of the universe?

« on: 05/06/2011 14:22:38 »

The universe does not have an edge, it is infinite, and it is essentially the same everywhere.

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Physics, Astronomy & Cosmology / Why does hot water sound different to cold water?

« on: 02/06/2011 10:38:51 »

Mine sounds exactly the same! The difference in density is negligible, so it would not affect the sound, and in any case, the frequency of a wave is not affected by the density of the medium, only the speed and wavelength are affected.

I suspect that the real answer is simply due to the hot and cold water being at different pressures and flow rates, because the sound is produced by the water hitting the sink. Try adjusting to the same rates and see if there is any difference.

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Physics, Astronomy & Cosmology / Why is light from the early Universe still around today?

« on: 01/06/2011 19:40:00 »

However, if it happened 520m years after the big bang and given that we assume that every point in space and time was in the same place at the Big Bang,....

Your error is in thinking that the universe began as a point, which is a common mistake - it was actually infinite at the BB. The light originated 13 billion light-years away, which is why it took 13 billion years to get here!

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Physics, Astronomy & Cosmology / How do they measure very low levels of things?

« on: 13/04/2011 10:48:47 »

I don't know the complete answer, but radiation monitors are well above the ground and measure radiation in the air, which I presume would normally be far less than at ground level.

http://www.kgw.com/news/local/Residents--118446824.html

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Physics, Astronomy & Cosmology / Where are we in the Universe?

« on: 11/04/2011 20:37:46 »

I have to say though I have never really felt comfortable that the Universe can be potentially expanding faster then the speed of light and yet at the same time is infinite!

I also have trouble with the idea that we can be standing still in our frame, a distant galaxy is also standing still in its own frame, yet the space in between is expanding! How can nothingness expand?

 In this sort of situation you simply have to accept what Science tells us, and not try to understand it in everyday terms, because our intuition is inadequate. Some people never learn that lesson.

 There are many similar examples in Relativity and Quantum Mechanics, and even Newtonian Physics sometimes violates our intuition (eg gyroscopes).

Is it really necessary that for the Big Bang theory to work there had to be nothing before?

No it isn't, and I have never understood why people equate the BB with the origin of the Universe.

To quote Scientific American on Looop Quantum Gravity:
    "Einstein’s general theory of relativity says that the universe began with the big bang singularity, a moment when all the matter we see was concentrated at a single point of infinite density. But the theory does not capture the fine, quantum structure of spacetime, which limits how tightly matter can be concentrated and how strong gravity can become. To figure out what really happened, physicists need a quantum theory of gravity.
    According to one candidate for such a theory, loop quantum gravity, space is subdivided into “atoms” of volume and has a finite capacity to store matter and energy, thereby preventing true singularities from existing.
    If so, time may have extended before the bang. The prebang universe may have undergone a catastrophic implosion that reached a point of maximum density and then reversed. In short, a big crunch may have led to a big bounce and then to the big bang."

http://www.scientificamerican.com/article.cfm?id=big-bang-or-big-bounce

I find this idea seductive because it allows the Universe to be infinitely old, just as it extends to infinity in the other direction of time, and also in space, which seems more elegant to me.

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Physics, Astronomy & Cosmology / Where are we in the Universe?

« on: 11/04/2011 16:17:33 »

To state that it happened everywhere at once would be like saying the Universe is infinite which it is not.

The universe does seem to be infinite, and always has been. To say that it is finite is to say that it has a boundary, which makes no sense, or else some weird geometry, which is not supported by observation.

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Physics, Astronomy & Cosmology / What is the simplest explanation of gyroscopic precession?

« on: 08/04/2011 17:08:38 »

Think in terms of angular momentum vectors.

The initial spin is a vector pointing along the spin axis. If you push down on the top of the gyroscope this imparts a small angular momentum vector horizontally, and at right angles to the axis. Adding these two vectors gives a new vector displaced sideways from the original vector, with the same inclination to the ground.

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Physics, Astronomy & Cosmology / Which way does gravity attract on objects with irregular shapes and densities?

« on: 06/04/2011 20:50:17 »

in the more general case, the object attracts things towards its centre of gravity whatever shape it is.

That is not true. Suppose we have a dumbell shape, ie two equal spheres connected by a light rod. The COG is the mid point of the rod, but an object near one of the spheres will be attracted towards it, not towards the COG. In general there is no easy solution.

Incidentally, the result for the inside of a sphere also applies to a prolate spheroid (and presumably an oblate spheroid) if the inside surface is similar to the outside surface - see page 19 of:

www.itp.uzh.ch/~justin/AstrophysicalDynamics/Lectures/lecturenotes.pdf

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Physics, Astronomy & Cosmology / Can we see rays falling on the Moon from the poles?

« on: 05/04/2011 17:21:10 »

I presume you refer to the moon's poles! The moon's axis of rotation is tilted by about 1.5 degrees to the plane of the Earth/moon's orbit round the sun, so at some times of year the sun would be that far above horizontal at the poles, and you would be able to see the Sun if you are not in a depression.

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Physics, Astronomy & Cosmology / Why do neutrinos have to have mass to oscillate and how is energy conserved?

« on: 03/04/2011 09:58:37 »

If a particle travels at the speed of light then from its point of view no time elapses as it travels from the Sun to Earth, so it cannot change from one kind to another. So if it does change then it must be travelling slower than light, and since its relativistic mass is non-zero its rest mass must also be non-zero.

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Physics, Astronomy & Cosmology / Could it be a good idea to form a new periodic table?

« on: 31/03/2011 16:03:53 »

Interesting fact from Wiki: "Neutronium is a proposed name for a substance composed purely out of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 (before the discovery of the neutron itself)"

http://en.wikipedia.org/wiki/Neutronium

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Physics, Astronomy & Cosmology / Does physics allow for a proton star

« on: 28/03/2011 10:56:54 »

The repulsive electric charge of a proton star would overcome gravity, and the nuclear forces are very short-range, so it would be impossible for the star to stay together.

There is also the problem of removing the electrons in the first place!

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Physics, Astronomy & Cosmology / Is there any correlation of lunar proximity and quake activity?

« on: 26/03/2011 16:11:54 »

You might expect that there would be a correlation with the distance of the Moon, and also with the phase of the moon, because the sun also has a tidal effect which reinforces the moon's when they are aligned. However, when you look at the data, if there is any correlation it is very small.

The Japanese quake was a week before full moon, and half way between perigee and apogee, so the moon cannot be blamed.

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Physics, Astronomy & Cosmology / Why do we only see one face of the moon?

« on: 26/03/2011 14:10:46 »

I have tried using two spheres, bearing in mind that the Moon rotates clockwise and the Earth anti-clockwise, but am still unable to grasp the concept.

That is not true - the Earth's spin, the Moon's spin, and the Moon's orbit around the Earth are all anti-clockwise when seen from above the North pole. That is why you are confused.

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Physics, Astronomy & Cosmology / Why was the moon closer to the Earth recently?

« on: 25/03/2011 09:39:43 »

The orbit of the moon is not a simple ellipse because of the Sun's gravity.

When the Moon is new it is closer to the Sun than the Earth, so the Sun pulls it more strongly than it pulls the Earth. This difference means that the Moon's orbit is extremely complicated. A further complication is the Earth's equatorial bulge. The result is that the direction of perigee moves around the Earth, and the distance at perigee also varies - between 1960 and 2040 the perigee varies from 356445km to 370354km.

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Physics, Astronomy & Cosmology / what is the outcome of Colliding black Holes ?

« on: 23/03/2011 20:09:00 »

Antimatter is affected by gravity in exactly the same way as ordinary matter, so they can collapse into black holes, in theory. The only problem is that there are no antimatter stars.

A BH is described entirely by its mass, spin and electric charge, so a BH formed from collapsing anti-matter would be indistinguishable from a normal matter BH.

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Physics, Astronomy & Cosmology / What is life? And is there life on other planets?

« on: 18/03/2011 08:51:41 »

The definition of life is really just a matter of semantics, and various ways of defining life have been proposed:

http://en.wikipedia.org/wiki/Life#Biology

Take your pick!

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Physics, Astronomy & Cosmology / Re: Was there an original association between the Sun and alpha Centauri?

« on: 12/03/2011 09:35:32 »

Stars which formed from the same nebula as the Sun can be identified by their motion, which will be at the same speed and direction as the Sun. Such stars are known (although I don't know any examples). but Alpha Centauri is not one of them - it has a substantial velocity relative to the Sun, so it would not have been nearby when the Sun formed.

Stars formed from the same nebula have a large range of sizes (eg Alpha centaur A,B and C), and solar-mass stars are fairly common, so any similarity is just a coincidence.

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Physics, Astronomy & Cosmology / Why don't terrestrial planets have rings like Saturn?

« on: 24/02/2011 16:37:57 »

If Earth had rings: