1

Physics, Astronomy & Cosmology / Re: Is uniqueness conserved?

« on: Today at 01:06:03 »

The confusion arises from the assertion of "specific coordinates". The relationship between any two events is a unique vector in spacetime, but that vector can be mapped onto any coordinate system you choose, including the possiblity of degeneracy if the extended vector passes through the origin of that system.

To give an example, suppose galaxy A explodes and emits a pulse of gamma radiation. After a thousand years, that pulse triggers the explosion of galaxy B which just happens to have moved into such a position that its gamma burst is indistinguishable  from that of A at the time they both reach Earth. Having no other information, our observer can only conclude that there has been at least one explosion, somewhere in the direction of B, whereas an observer on Pluto would know that there were at least two explosions 1000 light years apart.

Time to resurrect the abbreviated  version of the Patagonian Cows. Three blokes in a train see two cows in a field.

Politician: "The vast majority of Patagonian cows are black"

Statistician: "On a possibly insufficient sample, the Bayesian postulate is that half the cows in Patagonia are black"

Physicist: "I saw two bovine quadrupeds, at least one side of one of which was black."

2

Technology / Re: Why are the temperature readings abnormally high

« on: Yesterday at 20:54:21 »

Check your data by googling "METAR FARO". Look for the "allmetsat" website. This gives you the most recent (METAR)and "best forecast" (TAF) data for all the world's commercial airports.

Check also for "obvious" errors - US reports will be in Fahrenheit, satellite infrared data may be visible bare ground (standard met report is air at 1.5 m above ground in the shade), and just to make it interesting, local time in Portugal is an hour behind the rest of Europe!

Then check for other anomalies. You'd expect Faro to be cooler than, say, Seville during the day and warmer at night, for instance.

And remember that "the region around" a coastal airport is going to be quite a bit hotter than the airport during the day if there's no cloud. The BBC forecast may well be based on airport data.

3

New Theories / Re: Do you want to be more clever than Einstein?

« on: Yesterday at 18:30:53 »

Reading a bunch of irrelevant drivel does not make one clever. Understanding relativity might.

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That CAN'T be true! / Re: Am I one of the great scientists? Another trial

« on: Yesterday at 15:13:48 »

Yep, that pretty well defines philosophy.

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Physics, Astronomy & Cosmology / Re: Does this equation mean anything?

« on: Yesterday at 12:18:10 »

Reality is described by combining all possible spacetime histories

So the integrals must go from t = 0 to the present, and you have to add K, the starting condition at t = 0. That's the bit that humbles cosmologists and climatologists, because as far as we know the integrals may be a lot bigger (the Big Bang) or a lot smaller (Steady State) than K.

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Physics, Astronomy & Cosmology / Re: Can we cool a point with precision?

« on: Yesterday at 12:10:26 »

Utrasound combined "search and destroy" has been a research objective for many years. It is beset by several problems associated with sound transmission in biological tissue

absorption en route
inhomogeneous tissue en route
differential speed of transmission 
inhomogeneous surface coupling to the transducer....

all of which get more significant at higher frequencies. But you need high frequency (short wavelength) to obtain a small focal spot. The equations are in principle solvable in real time but in practice the "point" is very fuzzy and damage to the surrounding tissue is difficult to avoid.

It turns out in practice that healthy biological tissue repairs itself quite well from a needle insertion, so a neater way of destroying a target is to insert a thermode through a cannula (using x-ray or ultrasound guidance) and heat or cool the tip with a Peltier junction, laser, or cold helium. You can also inject a variety of therapeutic or cytotoxic agents such as ozone or acetic acid to stimulate or kill the target. 

7

Physics, Astronomy & Cosmology / Re: photon violates energy conservation?

« on: 20/07/2019 21:00:30 »

You have done work by moving the second atom. It doesn't have to be a photon. Imagine a bullet fired from a stationary gun, hitting a moving target. The impact energy depends on the relative velocity of the bullet and target.

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Physics, Astronomy & Cosmology / Re: Are all photons mediated in the same way through the quantum vacuum

« on: 20/07/2019 13:36:47 »

how a photon is propagated in QED

There's the rub. It is analagous to how a mouse runs in a cartoon - not how a mouse runs in real life. QED, like all physics, is an attempt to create a mathematical model of what actually happens.

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General Science / Re: Wouldn't Earth moving through space be a big problem for time travel?

« on: 20/07/2019 09:25:48 »

If everything is moving in x,y,z as t varies, then you will also move in x,y,z with t, so whilst the stars and planets will appear to whizz about as you move forward or backward in time, your position as the origin of all you observe, will not change (though the chair will rust and crumble as it gets old, or revert to iron ore and a live horse as it gets young).

The real problem, however, is to prevent yourself becoming dust or reverting to an ovum.

10

Technology / Re: Were the moon landings faked?

« on: 20/07/2019 07:48:36 »

Or, having decided that the private sector must carry the nonexistent risk of building and running hospitals,

That's not any competent government; it's a Tory one.
They did that to undermine  public sector work.
Everyone knows that.

I am enternally grateful to a Tory government for its obsession with reducing the size of the civil service. They gave me 35 years' pension for 25 years' work, and  a cash bribe, all for the sake of a few votes (as if anyone really cared anyway). And a year later they recruited two blokes to do my work. 

But myopic idiocy comes in all colors. It was a Labour government that built the R101 and scrapped TSR2. And both parties shared the Brabazon fiasco.

11

Technology / Re: How do continuous glucose monitors access blood?

« on: 20/07/2019 07:32:49 »

Any sensor requires a fixed wetted surface area (electrochemical) or path length (optical) - not easy to achieve at the pointy end. A "tip and sleeve" electrochemical sensor can work for a while but they are all subject to the problems of erosion, contamination, or simple phase lag (the sample you have in  your optical tube is not representative of the present blood glucose level) if sampling is by osmosis or diffusion.

It is a very annoying problem. The physics and chemistry of glucose measurement are well established in vitro, but in vivo engineering is orders of magnitude more complicated. I've been aware of patents and projects appearing over the last 40 years, with no really satisfactory product reaching the market.

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Technology / Re: Were the moon landings faked?

« on: 19/07/2019 23:28:47 »

Government work got us to the Moon.

and once the political goal had been achieved, cancelled the program.

Governments seem on the one hand unable to control costs (e.g. HS2) and on the other, to award contracts to the lowest bidder regardless of his ability to deliver (Seaborne), then compensate those who were not invited to bid (Eurotunnel) with the third hand, without establishing the need for any of the projects it the first place.  Or, having developed an excellent and functional product (TSR2), scrap it, destroy all the jigs and documents, and contract to buy a machine (F111)  that had never flown, at a price that climbed faster than the plane itself. Or, having decided that the private sector must carry the nonexistent risk of building and running hospitals, shell out uncontrolled service fees or pay huge deposits to companies that go bust as soon as their directors have bought their yachts.

Not that it matters. It's your money they are spending, and you have to pay your taxes whether you like it or not.

Alan Shepherd was asked what he thought about during a countdown. His reply: "Ten million moving parts, each made by the lowest bidder."  Pilots are expendable, accountants are essential.

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Physics, Astronomy & Cosmology / Re: Does this equation mean anything?

« on: 19/07/2019 23:19:10 »

Thanks for that! I'd disagree with the explanation as Schrodinger's Ψ isn't "reality"!

 |Ψ²| is the probability of an event, IIRC, and I'm not entirely sure why the integral necessarily invokes an exponent, other than for aesthetic reasons.

But wiser heads abound, I'm sure.

14

Technology / Re: How do continuous glucose monitors access blood?

« on: 19/07/2019 23:13:50 »

Not particularly well, it seems. I've reviewed several research projects using CGM sensors and in each case the recommendation from the researchers or the manufacturers has been for frequent recalibration - as often as twice a day - against a standard fingerprick sample.

From diabetes.co,.uk

Continuous glucose monitoring isn't blood glucose monitoring as the sensors with a CGM machine are placed into your body but not into the bloodstream.
The sensors measure the glucose in your interstitial fluid - the fluid in and around your body’s cells.
The relationship between glucose concentrations in interstitial fluid (ISF) and blood has generated great interest due to the possibility of gaining up to 288 glucose level readings a day without having to do finger pricks.

It's a difficult problem. Electrochemical sensors generally require a flowing liquid to remove reaction or electrolysis product from the electrodes, and static body fluids are remarkably corrosive to electronic gubbins.

15

Physics, Astronomy & Cosmology / Re: Does this equation mean anything?

« on: 18/07/2019 22:54:10 »

There's some rubric at the foot of the poster as shown on the P I website, but I can't read it. If you have the actual poster, I'd be interested to know what it says! However if you want to sum up everything that happens in the universe then ΔS > 0, which is sufficiently depressing for any teenager.

16

Technology / Re: Were the moon landings faked?

« on: 18/07/2019 20:34:33 »

The giveaway is that the photos of the other side of the moon don't look like the real thing we can see from this side. Shoddy graphics or interesting selenology? I know which conclusion a government committee would support, on grounds of cost.

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Physics, Astronomy & Cosmology / Re: Does this equation mean anything?

« on: 18/07/2019 20:30:43 »

The square root of the probability of something happening is the integral of a whole bunch of other stuff, some of which apparently depends on the answer itself.

I think a picture of a cat under the Sword of Damocles suspended by a question mark pretty well sums up what Schrodinger had in mind.

18

Technology / Re: Were the moon landings faked?

« on: 18/07/2019 18:04:00 »

Of course they were faked. But why? And why didn't the Russians fake them first? That's the real conspiracy, folks.

19

Technology / Re: How reliable is the Kibble Balance?

« on: 17/07/2019 19:32:44 »

And if my tide tables are to  be believed...

...Then they can be used to supply the correction needed.

Alas no, they are crude predictions, good enough for entering a harbor or transiting a narrow passage, but don't claim to tabulate g to parts per billion on land.

So to use the Kibble balance you have to measure g each side of your mass determination

Which is fairly easy.

What would you use instead (to define the Kg)?

A Kibble balance.

"Pre-nuclear" lead and steel are priceless if you are in the business of measuring fallout.

I have some old lead for screening stuff.
It also helps to get it from a mine where the background uranium levels are low.

Sadly, manmade contaminants like plutonium and iodine get into the refining process and screw up the best forensic gamma spectrometry. I'm currently watching "Chernobyl" - somewhat oversimplified but it shows the importance of precise analysis. We used pre-nuclear shielding to measure the acquired activity of UK civilians immediately after the event, with some very interestng results.

20

Technology / Re: How reliable is the Kibble Balance?

« on: 17/07/2019 14:11:41 »

Except for the last sentence of that reference. Comparing a synchronome pendulum with an atomic clock

 

His data revealed the clock was so sensitive it was detecting the slight changes in gravity due to tidal distortions in the solid Earth caused by the gravity of the Sun and Moon.

And if my tide tables are to  be believed, that's a twice-a-day sinusoid with monthly and quarterly variations of amplitude. So to use the Kibble balance you have to measure g each side of your mass determination, and before you know it, you have a lab full of vacuum pumps, rubidium clocks, lasers and GKW, plus your ultrastable electrical supply, cryogen handling kit...and then somebody stores surplus lead blocks* in the basement (see discussion of Cavendish, elsewhere on this site).

 
*no joke! "Pre-nuclear" lead and steel are priceless if you are in the business of measuring fallout. Within my undistinguished career, one overzealous administrator sold 150 tons of prenuclear lead for scrap without asking why we kept "a roomful of junk" and a manufacturer petitioned Parliament for permission to salvage a 1918 18-inch naval gun barrel from a war grave.