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Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: Today at 14:59:25 »

Some  people said that acceleration is relative

An accelerometer consists of a mass attached to one end of some kind of spring, the other end of which is attached to the object being accelerated. An observer within any accelerating object will see a deflection on his accelerometer. Acceleration is therefore absolute.

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General Science / Re: Does All Of Mathematics Come Down To Simple Arithmetic?

« on: Yesterday at 10:39:31 »

I have seen an undesirable side-effect of introducing computers to the classroom. In my kids' primary school I met a group of 10-year-olds who defined a circle as 360 straight lines.

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New Theories / Re: Universal Utopia? What's The Universal Terminal Goal?

« on: 08/10/2024 23:43:27 »

Should we care about the survival of our species?

Yes and no. Obviously every normal person cares about the survival of the next generation, but evolution pretty well guarantees that multicellular organisms evolve, so "species" is a time-specific label. A chicken is what eventually derived from  the dinosaurs that survived the cometary impact, and it has very little in common with a diplodocus. 

Should we get rid off "contaminating" DNA from other species? How much genetic changes are allowed for our future descendants/successors?

We are what we are - the concept of "contamination" is meaningless.

Assuming that homo sapiens spread from east Africa, and that migration was mostly one-way, it is likely that Ethiopians are the least "contaminated"  group, with caucasian and asiatic peoples having significantly more bits of other hominid DNA. The fact is that "species" is not a precisely defined term, and it is pretty clear that stirring the gene pool tends to suppress undesirable characterisics such as color blindness or hemophilia.   

Common sense and observation support Darwinian selection: beneficial genetic changes will dominate, and at some point the dominant product will be sufficiently different from its ancestors to merit classification as a new species.

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Just Chat! / Re: Is there a universal moral standard?

« on: 07/10/2024 16:05:22 »

Has it violated the Geneva Convention?

Only to the same extent that the Allies did in WWII, and probably to a lesser extent.

Problem is that the Convention followed WWII when civilian casualties ran into the tens of millions (far  more than combatant casualties), so protection of noncombatants plays a significant part in the post-1949 rules of war.

The bleeding hearts now complain about civilian casualties where the enemy's armed forces are embedded in or under civilian establishments, which makes it impossible to project a just retaliation or to eliminate a threat from ground-based missiles without incurring significant noncombatant casualties.

The IDF attempts to minimise civilian casualties by issuing warnings of forthcoming actions but the destruction of infrastructure, and consequent depletion of civilian resources, remains inevitable.

The Convention necessarily acknowledges the right of States to self defence and hot pursuit of those that attack it. So on the basis that some modern warfare does not take place in trenches on open farmland, much of the Convention is irrelevant  and it behoves civilians not to give succour to those who wish harm to another State. 

Sensible response from an ex-CinC of the Lebanese armed forces on TV last week, suggesting that the official army should not interfere in an Israeli ground operation against Hezbollah. If only the general population of countries infected by such filth could see beyond religion and think about civilisation instead. 

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Just Chat! / Re: Why do women have so many clothes?

« on: 28/09/2024 22:25:29 »

"Goeswiths".

The problem often starts from the bottom. One wet day, you discover that your strappy summer sandals really aren't suitable for standing in the rain, so you buy some cheerful red lace-ups. But you can't wear them with  a skirt and stockings so you buy some socks and a pair of jeans, but now you need a belt to hold up the jeans but that ensemble doesn't go with a cream handbag  so you buy a brown one for shopping and it looks ridiculous with a yellow cardigan so you need a blue sweater but that has a plunge neckline so you need a new bra and black is so nice but you can't possibly wear a sheer white blouse over it as you aren't a student any longer so a sensible red linen blouse sets off the sweater and as it's cold perhaps a chiffon scarf. All a bit dowdy now, so some big earrings to reflect the shoes but it's still raining so perhaps a leather jacket? Very biker-chic but you won't have time to change before going out to dinner so just add some heeled shoes so you can leave an impression on your friend's wooden floors, but they look ridiculous with socks and jeans so we need a skirt and tights. Keep the red blouse and ditch the blue sweater. Perfect, but not with a leather jacket, surely? So add a cream woollen coat. And a black handbag to match the shoes. And less flamboyant earrings.  Not sure about the scarf.......

And tomorrow is an office day. Grey suit, white blouse, no problem, but not with red shoes and a cream coat, surely?

Invited to a formal dinner with an erstwhile Boss, I watched her work through a dozen agonising permutations and then discovered that my dinner jacket had miraculously shrunk over the past several decades. Walked into the gents' outfitters and said "dinner jacket". Salesman looked at me and said "Rack on the right, try 46 regular. Blue or white shirt?"  Job done in 10 minutes, served as uniform in a dance band, will probably wear it in my coffin.

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Technology / Re: Nuclear generation produces green energy?

« on: 27/09/2024 16:36:57 »

To collect it as carbonate would involve huge quantities of a basic substance

..... such as calcium oxide, made by heating calcium carbonate  to drive off the carbon dioxide.....or sodium hydroxide, made by electrolysis, using electricity made by, er, burning carbon......

Green plants are the only sensible sinks for CO2, which they turn into food and building materials.

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New Theories / Re: what is temperature?

« on: 11/09/2024 18:43:01 »

Try

https://electronics.howstuffworks.com/led.htm

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Question of the Week / Re: QotW - 24.09.06 - What is the shutter speed of the eye?

« on: 01/09/2024 22:57:24 »

This means they can collect a lot more photons, under the same conditions.

Er, sort of. What matters is the brightness of the image, and for a given object this is principally determined by the ratio of aperture to focal length of the lens. This is conventionally specified as an inverse ratio f/n and for most cameras the largest aperture is around f/2, fairly close to the fully dilated human eye at f/3. Telephoto lenses bigger than f/4 are a bit unwieldy.

I heard that the human eye requires two photons to strike the same cone cell within a short period to register a flash of light.

Interesting. The same applies to photographic film. You need two visible photons to strike a single grain in a short time for a latent image to form. Under very low intensities, this causes "reciprocity failure" where the apparent sensitivity of the emulsion decreases with decreasing image brightness.  Astronomers used to "pre-fog" their plates to increase sensitivity - something of a black art probably lost nowadays thanks to  CCD imagers.  It also explains why fine grain photographic emulsions are less sensitive (typically ASA 50 - 64) than coarse-grain (ASA 1000) materials.

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Question of the Week / Re: QotW - 24.09.06 - What is the shutter speed of the eye?

« on: 30/08/2024 13:17:31 »

Given that single photons produce visible Cherenkov phosphenes, the minimum detectable event is probably of the order of 10^-18 seconds.

This is quite different from the subsequent processing time required to distinguish between events. Raster-scan television screens and mechano-optical cine projectors produce an image of continuous motion if the sampling frequency exceeds about 16 frames/second, and even when individual cine frames are clearly blurred (say taken at 40 mS intervals)  the projected "moving image" can appear as sharp as a still photograph.

LED lights driven at < 10 Hz may appear to flicker but at > 20 Hz the light output appears continuous.

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New Theories / Re: How do we acquire language?

« on: 28/08/2024 18:31:05 »

Never mind the other bullshit, but Sultans of Swing has to be the best rock number ever. Closely followed by Love Shack.

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Just Chat! / Re: Is there a universal moral standard?

« on: 20/08/2024 11:14:14 »

What's immoral about a mosquito procreating? Or a parasite colonising a new host? People procreate, and some even want to colonise other planets. What's the difference?

Fact is that different species have conflicting goals, so no possibility of a universal moral standard.

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New Theories / Re: What's the unit of Torque?

« on: 19/08/2024 18:32:30 »

You are just adding to your own confusion and helping nobody. Force x moment arm = torque. What's the problem?

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New Theories / Re: What's the unit of Torque?

« on: 18/08/2024 12:26:26 »

If you put down Gemini and pick up an elementary physics textbook, it will tell you that I = Σmr², as every schookid knows.
Why do you waste your time consulting a long-winded mechanical idiot?

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New Theories / Re: What's the unit of Torque?

« on: 15/08/2024 21:36:43 »

I think you need to first understand what the meaning of a concept as it's currently understood by most of its users.

Not on a science forum. There are formal and precise definitions of important words like torque, power, energy, velocity, speed, exponential....which are not currently understood by most of the people who (mis)use the words.

I think the correspondents in this forum are well acquainted with Newton's laws, even if the people who feature in some videos aren't.

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New Theories / Re: What's the unit of Torque?

« on: 13/08/2024 18:17:14 »

[Quote ]from: Bored chemist on 11/08/2024 23:44:06
The units of both are mass length squared per time squared.

this is so wrong.  It seems to presume that energy and torque are the same thing, and then applying a relativistic notion of mass-energy equivalence to torque.

No, it's purely classical.

Work = energy = force x distance, MLT^-2 x L
Torque = force x distance MLT^-2 x L

Which is why you can measure torque with a spring.

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New Theories / Re: What's the unit of Torque?

« on: 11/08/2024 16:52:55 »

I think one would have to do an integration of the torque over the full winding cycle as the torque will not be constant.

As the tightening torque increases with each turn of the key, I think the final torque equals the stored energy, same as when you stretch a bolt by tightening it. The difference is the much smaller hysteresis and energy loss of a spring.

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Just Chat! / Re: Is there any greater ******** than Elon Musk?

« on: 07/08/2024 23:00:24 »

Elon should be barred from twitter

But he owns it, idiots subscribe to it, and journalists rely on it as a substitute for news.

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New Theories / Re: what is temperature?

« on: 07/08/2024 16:30:26 »

Whatever else you do in life, please do not attempt to learn or teach physics from Gemini. Utter crap.

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Technology / Re: Nuclear generation produces green energy?

« on: 06/08/2024 15:58:11 »

The statutory occupational dose limit is 20 millisievert per year, 20 times the "public" limit. When designing any publicly-accessible facility you need to adopt a dose constraint of about 0.3 mSv/year or less.

Submarine crews and shore maintenance personnel are monitored and rotated to keep their dose "as low as reasonably practicable" given the inevitable exposure associated with their employment, but the reactor shielding for any vehicle is necessarily a compromise between weight and safety, which is why there are no nuclear-powered aircraft. To bring the reactor into a permanent civilian facility you would need to build a whole lot more shielding, which demands concrete and steel, which consume a lot of fossil fuel. On patrol, of course, sea water is a very effective and zero-cost radiation shield when the reactor is running at full steam, so you only need to shield the forward bulkhead (assuming the reactor is at the stern) against maximum flux. You can't run the part-shielded reactor at full chat in a crowded harbor, but you'd need to if it is intended to supply the electricity grid.

Civil aircrew generally receive about 4 mSv/yr but there is some debate over whether this is an employment dose since (a) the source is entirely natural and  uncontrollable and (b) it's still within the range of natural background doses to which some populations are exposed (up to 8 mSv/yr in parts of Cornwall, and a lot more in some other countries)  with no evidence of harm. So we have monitoring programs and advisory crew rotation but so far, no lawsuits.

Nuclear submarines generally work at about 200 MW, which won't make much impact compared with Drax (biomass) or any of the coal, nuclear  or gas stations opened in the last 50 years, which run at 2000 - 4000 MW. You could probably run a big hospital from a submarine.

And rerturning to acsin's plan, why build a submarine anyway? A land-based nuke would be a lot cheaper, though still uneconomic.

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Just Chat! / Re: Where do I get my confidence to challenge established theories?

« on: 04/08/2024 18:07:54 »

Non-mainstream ideas are less likely to get public funding.

One of the great flaws of public funding, alas. Your brilliant hypothesis and amazingly simple experiment will be judged by lesser minds who prefer to sit on committees rather than get their hands dirty.

The way to get research funding is to find a private company with a problem whose solution will make money.