1

Technology / Re: Does wi-fi harm the environment?

« on: 03/03/2023 23:09:04 »

'<X>G' is just the generation of the standard used to communicate. It's got nothing to do with increased danger. There's no reason to think that 5G is more harmful than 3G or 4G or that 6G would be more dangerous either.

2

Plant Sciences, Zoology & Evolution / Re: Is it possible to ride a kangaroo?

« on: 21/02/2023 21:34:52 »

I heard about a military helicopter simulator, where one of the conditions was that it would emulate the action of kangaroos, which can give away your position by fleeing from an invisible helicopter.
- In the acceptance tests for the simulator, a helicopter approached a mob of kangaroos, and they bounded away in a very realistic manner.
- Then one of the kangaroos stopped, turned around, and fired a rocket-propelled missile at the helicopter
- It turned out that in simulating the mob of kangaroos, the manufacturer had repurposed an existing model for a platoon of infantry - they changed the icon, lengthened the stride, and dialled up their anxiety. They forgot to disarm them.

On the upside, the pilots avoided kangaroos very well after that.

Task failed: successfully!

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Physics, Astronomy & Cosmology / Re: How important is it to recreate Earth's gravity on a manned spaceship?

« on: 19/02/2023 02:15:19 »

Because it's not real gravity.

4

Physics, Astronomy & Cosmology / Re: How important is it to recreate Earth's gravity on a manned spaceship?

« on: 18/02/2023 16:44:52 »

There's two propulsion technologies in use today. Rockets and ion/plasma drives. Rockets generally pull a few gs for about ten minutes or a few tenths of a g for an hour or so. Ion drives can pull milligees (due to the power/weight ratio of practical power supplies- carrying the weight of the power supplies limits the acceleration).

There's nothing, other than an infeasibly big rocket, that can generate 0.1g for months. That would be a tremendous advance if anyone worked out how to do it.

As an exercise, take a one tonne capsule and calculate the work done to do that from force x distance. You'll find it's ... large.

5

Physics, Astronomy & Cosmology / Re: How important is it to recreate Earth's gravity on a manned spaceship?

« on: 18/02/2023 02:30:46 »

However since Martian gravitation is only about 0.3g there is no need to replicate Earth's gravitational acceleration throughout the trip.

One interesting factoid: nobody knows what the minimum g-force is for human being's long term survival.

All long-term experience is either at 0g or 1g, it's unknown whether humans can survive at 0.3g.

It is left as an exercise to the reader to choose between powered deceleration at > 0.1g, say, during the last few months of the trip,

That's completely beyond current propulsion technology.

6

Technology / Re: Does wi-fi harm the environment?

« on: 17/02/2023 02:08:29 »

Wi-Fi operates at 0.1 watts. There's no known harm at such low levels. A cell phone transmits on the cell phone frequencies at up to several watts. There is some evidence of issues if you hold a cellphone to your head while making phone calls.

7

That CAN'T be true! / Re: Can I get infinite "green" heat from my barn?

« on: 16/02/2023 23:36:31 »

Interestingly, a semiconductor thermocouple pair can have up to 30% efficiency, and a heat pump COP can exceed 4.That looks like a net gain!

Nope. Show your working.

8

That CAN'T be true! / Re: Can I get infinite "green" heat from my barn?

« on: 15/02/2023 00:09:01 »

Theoretically, if the heat pump and thermopile were perfectly reversible processes you might well be able to get back all the energy you used to pump the heat that performed the round trip. But they're not perfectly reversible devices. And further, a lot of the heat you pumped in leaks out through the walls, ceiling and floor, and so cannot be used to generate electricity anyway. So there's inevitably a gap.

9

Plant Sciences, Zoology & Evolution / Re: Is eugenics possible?

« on: 14/02/2023 23:50:04 »

Mostly it's not feasible at all. For single gene heritable traits, you might be able to breed a particular feature out of humans pretty rapidly, but for polygenetic ones it can take hundreds of generations to remove them.

10

The Environment / Re: Is global warming man-made?

« on: 12/01/2023 21:45:32 »

Exxon scientists calculated the CO2 levels rise due to fossil fuel emissions and the resultant rise in global temperatures back in the 70s and 80s, and it's tracked very well what they expected:

https://www.theguardian.com/business/2023/jan/12/exxon-climate-change-global-warming-research

11

The Environment / Re: Is global warming man-made?

« on: 07/01/2023 04:19:01 »

That makes sense, because, in your head, CO2 is no longer a greenhouse gas, and doesn't cause production of water vapour, which is an even more potent greenhouse gas. Oh wait, that's just in your head.

No. The overwhelming scientific consensus is that the anthropogenic increase in CO2 is causing global warming.

12

Physics, Astronomy & Cosmology / Re: Why in the cold are people throwing hot water into the air?

« on: 06/01/2023 05:40:38 »

My understanding is that it only freezes well with boiling water:

13

The Environment / Re: Is global warming man-made?

« on: 05/01/2023 23:01:00 »

No, the physics haven't changed, the effect of CO2 on the Earths temperature is extremely large, small differences have large effects, and humans have been pumping CO2 into the atmosphere as fast as they can.

14

Geology, Palaeontology & Archaeology / Re: How to turn powdered rock into hard, solid rock?

« on: 28/12/2022 05:06:39 »

Yes, the general description for what you seem to want to make is: 'concrete'

You may have heard of it.

There's two main types: mortar based and polymer concrete

Almost any plastic will work for polymer concrete, if you really want you can use a thermoplastic and then you can rework it if you screw anything up.

Thermoset plastic with rock in it is used for concrete worktops, they frequently use acrylic, but epoxy or vinyl or polyester should work fine too. It's easy to test, just get some plastic and start mixing. You don't need or want a whole lot of plastic to stick powder together, it just fills in the gaps between the powder particles.

It helps to have different particle sizes. The small particles fill in the gaps between the big particles, and the glue sticks the whole lot together. You generally want to use as little binder as possible, the binder is expensive and the aggregate is typically cheap.

15

General Science / Re: How much water vapour in human breath

« on: 23/12/2022 10:52:23 »

The pilots breath faster when under stress, but I think a bigger effect would be that pilot sweat more, and I think that's where most of the moisture comes from.

16

General Science / Re: What underlies a detailed autobiographical memory?

« on: 21/12/2022 17:32:27 »

Actress Marilu Henner has essentially perfect autobiographic recall, she's one of a handful of people worldwide that has that.

From her description it sounds to me like she's doing mnemonic techniques. She remembers a visual, spatial calendar which she imagines has pictures for each day, and has linked the detailed memories of individual days to those pictures.

I suspect that most people could do this with the right training. Mnemonics are very powerful.

17

General Science / Re: Simple finite number of steps to shuffle a rubis cube with random large integer?

« on: 20/12/2022 15:47:16 »

Is the OP on this thread a bot or only the 'reply' by ChatGPT?

18

Technology / Re: Are solar panels worthwhile?

« on: 20/12/2022 05:13:57 »

Emphasis is mine:

Average output of a solar unit in the UK is 10% of its rated power, so that's 25600 kg of CO2 to produce 1 kW for 20 years (performance falls off towards the end of life) - 175000 kWh, say 0.156 kg CO2 per kWh. That's about 2.5 times the energy per unit CO2 that you'd get by burning coal, or 1.5 times what you'd get from diesel fuel, so it's marginally economic as long as you don't need to store the electricity, in which case the climate would probably be better off with coal.

If you need to replace all your internal combustion and gas heating systems in order to use solar electricity, and build electrical  storage systems, the carbon break even period looks more like 200 years.

I'm missing something? Well, the original claim of this entire thread was that it took 2560 kg of CO2 to make 1 kW of solar panels:

https://www.linkedin.com/pulse/rapid-fall-solars-embodied-carbon-chris-worboys

But this is an out of date claim going back to 2015. The figure in 2020 was 76% lower 615 kg CO2e/kWp:

https://www.linkedin.com/pulse/rapid-fall-solars-embodied-carbon-chris-worboys

So actually when you put these two posts together:

100%-76% = 24%

24% of 0.156g/kWh is 37g/kWh.

Compare that with coal which is usually more like 800g/kWh or even natural gas in CCGT power plants which is more like 350g/kWh.

37g/kWh is around the number I've seen quoted elsewhere, and the carbon intensity of solar panel's production is still going down.

Solar panels are RIDICULOUSLY low carbon.

19

Technology / Re: Are solar panels worthwhile?

« on: 19/12/2022 23:19:52 »

Yes, they can be worthwhile if you want to set up a society in the forests without any human intervention, then it is one of the only few choices.

Yeah, that's not what I've found. We've just put down a deposit for an on-grid solar panel/battery system here, and we don't live in a forest. The panels will provide about half the electricity over the entire year, and the battery will help store significant amounts of cheap off-peak rate electricity for use during the day as well as buffering usage and production during the day and night. The long term cost for the solar is about 8p per kWh, and hopefully should have a 30 year plus life, with under 15% degradation. Based on careful modelling I expect the system to pay down the cost in about ten years (an APR of about 10%, which under the current economic climate is really good), but the exact rate depends on the tariff costs, but the curve is quite flat. The financial optimum seems to be around where the average generation by the panels is used entirely within the household over summer, which largely prevents importing from the grid, and where the battery is big enough to fill out the production in the 'shoulder months' of Spring and Autumn with stored off-peak electricity.

Off-peak electricity is lower carbon because it's baseload and wind and nuclear are a higher percentage on average, and solar generation during the day is low carbon too, contrary to the misinformation that has been posted here.

The cheapest off-peak right now are the 'EV tariffs' which give you just 4 or 5 hours to charge the house battery at super low tariffs of 5-12p/kWh. Economy 7 can also be used but isn't quite as good. During the winter, the battery doesn't have enough capacity for the whole day, so expensive 'peak rate' electricity is imported, which is even more expensive than normal, but the ratios are such that it's still somewhat cheaper than conventional tariffs over winter, and the rest of the year, the costs are ridiculously low.

Basically, the core idea is to run the household on off-peak and solar power as much as possible, because it's simply far cheaper to do so. In winter, using wind power is the way to go, but fitting wind turbines to homes is probably a bad idea, but the grid is increasingly wind powered, so importing electricity in winter is likely to be a good strategy going forward.

20

General Science / Re: How does heating from air conditioners vs radiators compare?

« on: 10/12/2022 16:05:26 »

The point is, they should be running the night rate flat out, even if it means going well above 18C. The heat will leak away slightly faster at a higher temperature, but the cost of heating is a third of the day rate. Depending on the insulation they should set the night rate thermostat to 25C or higher, and even run fan heaters on the cheap rate to get the temperature up. Any electricity used on the day rate means they messed up.