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General Science / Re: When do YOU die in a many worlds interpretation?

« on: 06/12/2019 23:14:43 »

You have a death sentence anyway. It's just that most people don't know when or how it will be enacted. There is no evidence of the existence of other you's - "many worlds" is just a mathematical tool for assessing probabilities.

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Physics, Astronomy & Cosmology / Re: What happens when both slits are observed by in the double slit experiment?

« on: 09/11/2019 07:37:47 »

QM theory says no amount of measuring of a system will allow you to predict it.

Be careful how you state this. The test of quantum mechanics is not merely that it explains obvious quantum phenomena like line spectra, but that it scales to classical mechanics for large assemblies. And it does.

The wave function of a billiard ball is negligible in comparison with its apparent diameter, so for all practical purposes (e.g. potting the black) it is adequately predictable. But its structure, mass and elasticity are all calculable from quantum mechanics.

Indeed the "measuring" test isn't fundamental to QM. The classical model of bouncing a photon off an electron sort of illustrates the problem of measurement influencing the measurand, but masks the inherent indeterminacy of Heisenberg's statement that Δp.Δx ≥ h.

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Physics, Astronomy & Cosmology / Re: What happens when both slits are observed by in the double slit experiment?

« on: 08/11/2019 19:10:08 »

When we fire bullets (particles) at a slit they will, as you said, go through one slit or the other and form the 2 slit shadow we expect.

No! There is a calculable probability that a bullet will, in effect,  "go through both slits". As Eddington said, "If a student of physics should fall through the floor and find himself in the room below, he would not be surprised but mildly elated at having observed an extremely rare phenomenon."

That's what I meant by quantum mechanics scaling up to continuum physics at a mesoscopic level. So far, it's only been demonstrated with large molecules like buckyballs, but the maths is sound.

You can work the model two ways: either map an enormous number of parallel universes onto one timeline to get "now", or wait a very long time in one universe for everything to happen. Problem is that once you get beyond 60 carbon atoms, the numbers become ridiculous.

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Physics, Astronomy & Cosmology / Re: What happens when both slits are observed by in the double slit experiment?

« on: 07/11/2019 13:25:35 »

You really need to abandon the particle/wave duality business to make progress in physics. Photons, atoms, indeed everything, behaves as it does because it is what it is, not what you choose to model it as.

Quantum mechanics gives us an excellent predictive model of the behaviour of very small things, but doesn't say what they "are". Continuum mechanics gives us an adequately predictive model of mesoscopic entities that allows us to build houses and fly to the planets. The important question to ask of quantum mechanics is "does it scale up to the observed behaviour of radio waves and billiard balls?", which it does. Likewise the test of relativity is "does it scale down to Newtonian mechanics if v<<c?", which it does.

The problem with poking a particulate photon through two slits is manifold.

1. Only half the energy can go through each slit, so the wavelength of the emerging "photons" will be twice as long - but it isn't!   

2. If we rotate the receiver, we will alter the time at which the two bits of photon reach it, so they can't interfere - but they do!

Equally, however, if we presume a wave passing through both slits, all the interference peaks will occur simultaneously, however weak the source (down to one photon at a time) - but they don't!

It gets even more exciting when we pass "solid" objects like electrons, atoms or buckyballs through a diffraction grating. There's no way they can disintegrate and recombine at the receptor (if we move the receptor further away, where does the recombination happen?  If we remove it altogether, have we created partial electrons wandering through space?) but they form the predicted pattern!

The answer: believe what you see, and choose the most appropriate model to predict what you might see next time, but don't be surprised if something else happens - it just means your model was incomplete.

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Cells, Microbes & Viruses / Re: Who is older?

« on: 25/10/2019 17:43:14 »

Legally, your birth date determines your age, because this is precisely known, and even determines the precedence of twins. Medically, your date of conception is what matters, at least for the first few weeks of life.

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Physics, Astronomy & Cosmology / Re: Was the Big Bang the beginning of the universe?

« on: 16/10/2019 08:18:51 »

"It has a topology, it has a shape, it's a physical object," philosopher Jim Holt said

Yet another instance of pretentious drivel from a philosopher. Why does anyone bother to invite such people to speak? If you define "nothing"  as an absence of physical objects, it cannot be one. And there is no other meaningful definition.

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Physics, Astronomy & Cosmology / Re: Is light an independent entity, or is it an effect of a larger mechanism ?

« on: 14/10/2019 10:32:25 »

The analogy breaks down (as do all classical analogies of quantum phenomena, eventually) if you alter the state of your glove, say by turning it inside out. According to QM, and indeed demonstrably, the other glove alters its state too, and in a shorter time than it would take for a photon to travel between them.

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Physics, Astronomy & Cosmology / Re: Is it possible for the laws of physics to change in time?

« on: 27/09/2019 10:13:21 »

With regard to it being no big deal, my question was also related to potential societal implications, and for 'thinking' in general.

Society as we know it, and rational thought, will probably not last the next thousand years. I think it unlikely that the last remaining rational being will have noticed any change in the laws of physics before the mob beat him to death for apostacy.

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Physics, Astronomy & Cosmology / Re: Is it possible for the laws of physics to change in time?

« on: 26/09/2019 18:01:18 »

The laws of physics are mathematical approximations to our observations. There is no reason why they should remain constant, and indeed if the Big Bang really happened, they probably didn't. The implication of discovered inadequacies or inconsistencies in our description of things  would be that we would have to find a better one.

We have already replaced Newtonian mechanics with relativity and continuum models with quantum mechanics. And now we can see bits of the universe like black holes and dark energy for which we have no adequate model. No big deal.

Whether the universe behaves consistently over time is actually a meaningless question - consistency is in  the timescale of the beholder.

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General Science / Re: Proving or disproving theories: how does science work?

« on: 24/09/2019 16:39:21 »

That's interesting.  I think that I am correct in saying that rules which apply here on earth e.g. gravity, are assumed (right word?) to be true not just in this galaxy but are thought to hold for the entire universe.  Could you put me right on that?

I've used it before, but here's an illustrative tale. Three blokes on a train in Patagonia, look out of the window and see a black cow and a white cow.

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

Statistician: "On a random but not sufficient sample, one could hypothesise that half the cows in Patagonia are black"

Physicist: "I can see two bovine quadrupeds. At least one side of one of them is black."

At present we have no reason to think that Newtonian gravity and Einsteinian relativity are not universal. However some observed behaviors require further explanation in terms of phenomena or entities not yet observed. See, for instance, "dark energy" and "dark matter". And although there is evidence consistent with a Big Bang, the laws describing that singularity are unclear.

You might care to think about my idea of "negaticles" - fundamental particles with charge, spin, etc., but with negative mass. They would have the property of repelling ordinary matter but aggregating to each other. We would be able to observe the repulsion as an expansion of the observable universe, but could we observe any other effect of their presence?

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Technology / Re: Is this a stunning breakthrough in petrol engine thermal efficiency?

« on: 24/09/2019 00:50:36 »

If you start with a full 12.5 kWh battery (standard fit for a BMW3) and 1 liter of gas, you would expect to cover about 2.5 times the distance on battery power alone (over 90% efficient) as on the gasoline, say 40 miles total. At 4.5 liter/gallon you could argue (incorrectly, but we are talking "advertising maths", not the real stuff) that this is equivalent to almost 180 mpg. 

Actual road test figures yield around 65 mpg with a brand new battery, because if you started with a full battery and one liter of gas you would only cover 40 miles before the machine stopped. You would then have to recharge the battery with engine power, which is way less than 50% efficient at converting gasoline to electricity and is just a waste of time - you might as well use the engine to drive the wheels directly.

Looking at actual figures for hybrid taxis (I use a lot of taxis) they get around 60 mpg because they recharge the battery from the mains whenever possible and generally only do short runs. Gasoline mileage on a long run without mains recharging rarely exceeds 50 mpg for a Prius, no better than a 2 liter diesel. The energetic value of a "self-charging hybrid" is in regenerative braking and short-term acceleration, hence the attraction for taxis and city driving. In a sustained cruise you are just lugging the extra weight of a dead battery. 

Fact is that you can't get something for nothing, but the tax on electricity is a lot lower than on gasoline.

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Science Experiments / Re: Writing a strong Research Paper

« on: 16/09/2019 14:50:09 »

Here's how to write a perfect science paper

Say what you did
Say what you saw
Say what you thought about it
Say how you tested your hypothesis, or suggest how others might do so.

Pages of "desk research" and prior references may explain why you did it, but that's frankly irrelevant. At best, it means that you spent a lot of time not doing an experiment. That may impress your peers, teachers and dinner guests, but not a third party reader.

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That CAN'T be true! / Re: Does mobile phone tower radiation pose health problems?

« on: 15/09/2019 09:21:32 »

Years back, I took part in a civil defence exercise  modelling the day after World War 3. Lots of cunning coded messages exchanged through CB radio. Of course anyone who had a functioning radio and was fit and safe enough to use it, probably had other assets, so the moment you broke radio silence you became a target for predators. We quickly learned that the secret of survival is not to broadcast your survival. It is reasonable to assume that other civilisations have reached the same conclusion, and we know that governments monitor our personal phone calls and politicians pay geeks to monitor anything you broadcast on antisocial media, so the threat posed by your smartphone to your life and liberty is a lot more immediate than cancer. 

In short, don't expect to hear from any alien life form.

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Physiology & Medicine / Re: which scans are best NMRI or PET

« on: 12/09/2019 23:45:00 »

Calculating "committed dose" is actually a lot easier for short life nuclides than long ones, since we don't have to worry about precise retention and excretion coefficients. It's quite a process of measuring the administered activity, estimating the decay throughout the imaging process, adding up all the detected activities, and assigning organ sensitivities to the bits where the labelled stuff ends up. Fortunately it's all been done many times so for a routine procedure the required total activity is calculated according to body weight and the committed dose is estimated from standard tables.

NHS hourly costs include a lot more than consultant fees. Assuming he is an in-house consultant he will have a secretary, a nurse, a lab technician, a registrar and maybe a couple of students directly in tow, plus all the secretarial, housekeeping and administrative overheads, rent, heating, lighting, amortisation of the capital kit……. £500 per consultant-hour is indeed pretty much what it costs to run an outpatient session in a teaching hospital. For comparison, it's a hell of a lot cheaper than keeping a fighter plane in the sky, and the pilot will be lucky to get more than £50 per hour.

Best wishes for a definitive diagnosis and successful treatment! 

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Technology / Re: How can renewable energy farms provide 24-hour power?

« on: 02/09/2019 19:03:12 »

Experience, though it was some time ago. The essence of a supercap is a very thin dielectric layer

C = ε_mε₀A/d

where ε_m is the relative dielectric constant of the dielectric material m and ε₀, of the vacuum. A is the area of the plates and d is the thickness of the dielectric. Modern dielectrics can have very high values of ε but the manufacturing process is always a compromise between practical values of A and d. Mechanical fracture or chemical failure at a point in the dielectric produces a local short circuit through which the capacitor discharges, with catastrophic results.

Things may have improved - I hope so!

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Physics, Astronomy & Cosmology / Re: If earth rotates why don't hanging items swing?

« on: 19/08/2019 23:38:33 »

Look at a Foucault pendulum. It uses the conservation of angular momentum to demonstrate the rotation of the earth.

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Physics, Astronomy & Cosmology / Re: Matchstick physics and central european myths

« on: 09/08/2019 23:35:30 »

Two possible explanations

1. Matches are made of dry wood, which floats. Some are waxed, so they never sink.

2. Nobody had cursed you.

If you let the match burn completely, you may end up with a carbon residue that might eventually sink, especially if you add a bit of soap to the water. Or you could use  vodka or petrol, in which case more of the matches will sink. 

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Physics, Astronomy & Cosmology / Re: Do we go round in circles?

« on: 07/08/2019 14:56:34 »

differentiating between a sequence, which converges towards a terminal value that it can never reach, one that converges towards no identifiable limit and one that converges towards an endless decimal fraction, does seem to be making little more than a conceptual distinction, however valuable the concepts might be in mathematics.

It's enormously important!

In the first case I can write down a rational number (in this case 1) that is just a bit larger or in this case smaller than  any term in the sequence. So if you reported your position every hour as 1.1, 1.01, 1.001...miles from my house, I would know exactly where to look for you.

In the second case, I would know you are horribly lost and not recoverable because you are moving away from me at about 1 mph.

In the third case, although I couldn't write down a rational number that tells me where you would end up, I know it would be less than 2.7183 miles away.

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That CAN'T be true! / Re: Does mobile phone tower radiation pose health problems?

« on: 05/08/2019 21:22:15 »

What would be the point of radiating downward?

The greater exposure to radiation comes from mobile handsets, not the repeater towers.

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Just Chat! / Re: What impact will BREXIT have on Science & Society?

« on: 04/08/2019 11:54:08 »

Was it a majority of pensioners that voted for Brexit, many of whom are now dead a year later?

Not many dead. About 5% per annum.

I voted for Brexit because I'm fed up with paying a membership fee to a club whose primary function is to bankrupt my country. I look forward to a time when I can once again recruit staff on the basis of ability, not nationality.