1

Plant Sciences, Zoology & Evolution / Re: Why is compost black?

« on: 04/01/2021 16:20:11 »

Thank you for a very cogent explanation! I'll pass it on to the grandchildren.

2

Physics, Astronomy & Cosmology / Re: Does spacetime bend only locally around objects?

« on: 20/08/2020 15:03:32 »

The influence of a gravitational field falls off as an inverse square law, so although it has a theoretical influence to infinity in practice it becomes very small (relative to its local intensity) very quickly. Having said that, a large black hole will influence the path of large stars at a considerable distance.
If you think about our sun at 150 million km it still influences the orbit of the earth and also our tides, and at 1.3 billion km it influences saturn.

By comparison, kicking a football is a negligible effect.
Whether our 4D is considered to be the surface of a hypersphere really depends on which particular theory you are looking at. Remember these are models and there are a lot of them 

3

General Science / Re: Who can find a more poorly behaved function?

« on: 26/06/2020 23:31:06 »

A nasty one to test student programs to find the roots of a function is:

y=e^-1/x2

This function has a root y=0 at x=0, but:
- It is a root of infinite degree, which means that root-finding functions will take forever to get there
- If/when the function finds the root, it blows up (unless you are using symbolic maths package of suitable sophistication).

4

Physics, Astronomy & Cosmology / Re: Do our thoughts have mass?

« on: 17/06/2020 23:06:14 »

Landauer's Principle calculates the minimum energy to change a bit of information. At room temperature, it's about 0.0175 eV.

We can assume that our thoughts result in changes to the state of neurones, which can be interpreted as a change in information. So there must be some minimum energy consumption due to our thoughts.

And, as Einstein showed, energy has an equivalent mass. So the energy consumed by your brain (around 12 Watts) must represent some tiny mass difference between what your brain consumes in the form of glucose and oxygen, and releases in the form of water and carbon dioxide...

See: https://en.wikipedia.org/wiki/Landauer%27s_principle

5

Cells, Microbes & Viruses / Re: Are 85 Covid-19 deaths ON AVERAGE a day per 60 milllion a reason to PANIC?

« on: 04/05/2020 22:01:12 »

There's a significant difference between rapid decisive action and panic. Indeed they are polar opposites. An immediate lockdown of all nonessential interaction would have prevented COVID spreading much beyond the initial dozen or so cases in the UK. And it wouldn't have been all that damaging: the economy picks up pretty well after Christmas and New Year when primary and secondary industries effectively close down for 5 - 10 days.

So the trick for future epidemics (and there will be more - nature is indifferent to the fate of humanity)  is to determine in advance what activities and industries are essential and how those workers will be segregated into nonoverlapping shifts and squads (the lights don't go out at Christmas), then how a short, sharp lockdown will be policed and essential supplies rationed and distributed. We have had blackout (once) and petrol rationing (a few times) imposed  in my lifetime, immediately and at the stroke of a pen. Taxes change overnight and everyone adapts. I've participated in plans, preparations and exercises  for a 7 day transition to nuclear war, with a reasonable chance that they would have succeeded in keeping the immediate survivors alive. You get a lot more warning of an epidemic, and if you impose early lockdown and quarantine, it can be contained and eliminated. But it takes long-term commitment and planning, which is anathema to modern government.   

This thread began 6 weeks ago with 85 deaths per day. Had we had sensible plans and decisive action, that could have been the peak, but faffing and fumbling about has led to daily totals of hundreds of deaths and thousands of severe infections, massive economic impact, disruption of health and social services, and a probable death toll exceeding 40,000 this year plus maybe a million rendered unemployable. All completely unnecessary, as demonstrated in Korea.

6p - proper planning prevents piss-poor performance!

6

Cells, Microbes & Viruses / Re: Are 85 Covid-19 deaths ON AVERAGE a day per 60 milllion a reason to PANIC?

« on: 04/05/2020 20:36:16 »

So it looks like the Nightingale beds may never need to be used if a vaccine becomes available quickly.

Roughly 40 years of research has yet to come up with an HIV vaccine.

7

Chemistry / Re: How can I find the point where a reaction goes to the opposite direction?

« on: 30/04/2020 14:52:29 »

Not if you have to push it both ways...

The point is that you don't.

Catalytic cycles with multiple elementary steps don't have to work equally well in both directions.

Yes they do.

Do you accept that, if you have an equilibrium (and the principle of microscopic reversibility says you always have), then the position of the equilibrium is the point where the backward and forward reactions have the same rate?

Do you accept that if the catalyst increased the rate in one direction more than the other, it would change the equilibrium constant?

8

Just Chat! / Re: Is There Credible Evidence That God Exists?

« on: 12/04/2020 12:32:35 »

No problem. Define God and list one experimentally verifiable quality or quantity that is uniquely possessed or demonstrated by it, to the extent that you can predict the outcome of that experiment and not ascribe it to any other cause. Otherwise, you preachin' to the choir, brother!

9

Plant Sciences, Zoology & Evolution / Re: If we can’t replicate life in a lab, how could it happen randomly?

« on: 17/02/2020 16:58:32 »

Why did life only generate once?

[ What evidence do you have for this assertion? Life as we know it probably evolved on Mars, the conditions elsewhere in the solar system seem favourable, and there are at least 40 000 000 000 000 000 000 000  potentially observable solar systems that we haven't begun to explore. Beware of the Kruger-Dunning syndrome. 

We don't see new life crawling around the tidal pools.

Possibly the best place for it to evolve, but (a) there's lots of competition in a tide pool and (b) there's something like 8 000 miles of coastline to explore in the UK alone. The chances of anyone finding a new bug and proving that it had no organic ancestors are pretty small - we haven't catalogued all  the "known" species yet.

Why does life have only one manner of replication? Is DNA the only answer?

I think the answer lies in the question. If you define life as being the effect of replicating DNA, there cannot be another.

10

The Environment / Re: How much does human heat contribute to global warming?

« on: 04/12/2019 23:41:31 »

An average adult male produces about 100-120 watts of body heat: http://large.stanford.edu/courses/2016/ph240/stevens1/
The current world population is about 7.7 billion. If you multiply the two, you'd get 770 - 924 gigawatts (although this is an over-estimate, since much of the population is made up of children). The total solar energy received by the Earth is around 173,000,000 gigawatts: http://news.mit.edu/2011/energy-scale-part3-1026 That would make the total body heat contribution from human bodies less than 0.00045% of the contribution from the Sun. So it's practically non-existent.

11

Physics, Astronomy & Cosmology / Re: What is this fifth fundamental force I have just read about?

« on: 25/11/2019 17:15:57 »

https://profmattstrassler.com/

This might be a good place to start.

12

Chemistry / Re: Help on how to prolong lava stage of thermite

« on: 15/11/2019 23:47:01 »

Because it is a metal, it is both excellent at emitting radiation,

Erm, actually, no. Shiny things are poor at radiating heat.

I have seen pictures of industrial plant where they store molten Iron in special insulated containers and transport it to a different part of the plant by rail.

The biggest factor in their favour is that they do it on a big scale.
That way, most of the metal is "far" from the surface and can't cool so quickly (you can look up the stuff on surface are to volume ratios to get the maths if you like)

That's entirely consistent with the first reply here.

Keeping "lava" molten for long periods will require either amazing insulation, or a lot of energy.

13

The Environment / Re: Why do clouds stay high up when they are heavier than air?

« on: 08/10/2019 17:47:50 »

Is a cloud gaseous water or condensed water?

yes


The boundary of the cloud is not a true edge: water is going in and out of the cloud all the time. But only within the region of the cloud is the aerosol stable. Any water outside of the cloud is either in the gaseous state, or is precipitations (solid or liquid).

A good example of this is the lenticular cloud that can form on the leeward side of a mountain.  The wind pushes humid air up the windward slope which condenses on the leeward side.  The cloud formed remains in position with respect to the mountain, but the moisture forming it is constantly being removed by the wind, as the same wind brings in new moisture.

14

Physics, Astronomy & Cosmology / Re: Are gravitational waves faster than light?

« on: 24/09/2019 18:19:46 »

I know not of the podcast in question, but an event like a supernova has the light being delayed by the shock wave needing to travel to the surface of something like a star going supernova.  The light is also not subsequently traveling in a vacuum.  Gravity waves on the other hand are unimpeded by any of this and get here first.  So do neutrinos, which don't even travel at light speed, but fast enough that light (given the initial delay) never manages to catch up.

15

The Environment / Re: Why are the suns rays hot some days and not others?

« on: 20/09/2019 10:12:22 »

If you consider the elevation of the sun, rays have a lot more atmosphere to pass through in winter, hence greater absorption of IR.
Also, if you consider the energy/m² in a plane perpendicular to the rays then consider the angle of ground relative to the rays you will see that the energy is spread out over a greater area in winter reducing the heating, and hence air temperature, next to the ground.
Obviously, if you are standing then you are closer to the ray perpendicular, in which case the distance through atmosphere has greater effect.

16

Chemistry / Re: What is the most dangerous group of elements?

« on: 19/09/2019 20:18:03 »

FFS!
What is it about SF6 that makes otherwise reasonable people- even scientists- forget basic science.

This is a pretty dense gas - how well would it mix into the stratosphere?

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/properties2.html

"Gases have three characteristic properties: (1) they are easy to compress, (2) they expand to fill their containers, and (3) they occupy far more space than the liquids or solids from which they form."

17

Physics, Astronomy & Cosmology / Re: Is there an equivalent of absolute zero when it comes to heat?

« on: 19/09/2019 14:35:52 »

Is the concept of an absolute, approachable but unattainable 0 any less ridiculous?

That’s more interesting than it looks, at first glance.  HUP tells us why we can’t reach 0K; is there a similar principle/law that tells us why we can’t reach infinity?  What about HUP?  I suspect, not, but I’m no expert.

"Infinite" is not a number…..

I think this might have something to do with it. 

18

Chemistry / Re: Why doesn't water burn?

« on: 19/09/2019 00:25:25 »

'Burning' is actually a redox process.
The hydrogen and oxygen in water are fairly stable redox wise, but only in comparison to other natural compounds.
Thanks to this, the oceans aren't literally on fire.
However, strong oxidizers do, in effect, 'burn' water.
A dramatic example is chlorine trifluoride: ClF₃, CAS 7790-91-2.
Upon contact with water (or almost anything else), violent reaction occurs.

TL;DR:
Anything can burn with the right incentive.

Note: I wanted to embed a good youtube vid showcasing the stuff, but can't link currently. Look up Chlorine Trifluoride - it's fun!

19

Physics, Astronomy & Cosmology / Re: Could LIGO "see" alien warp technology?

« on: 01/09/2019 23:56:45 »

Oops! Overlap with Colin2B...
It's a bit hard to say, given that we know of no practical way to make such a warp drive.
- Some estimates have put the amount of mass/energy to create an Alcubierre drive at greater than the mas/energy of the universe
- That would certainly have an impact on the Earth if someone built one here.....

But if there were some practical way of creating such a drive
- And that it did radiate gravitational waves
          - Just like a supersonic plane radiates shock waves
          - This would be a continual power drain on the drive
          - I imagine designers would try to minimize wasted energy
- And the gravitational waves had a component in the right frequency range (about 50Hz to 1kHz for LIGO)
- Then it might be possible to detect it

I imagine that gravitational waves from a passing spaceship:
- Would be stronger, the closer the ship was
- Would be a single or double "blip" (like a supersonic shockwave), not the multiple cycles of oscillation that is currently being dredged out of the noise by the algorithms examining LIGO/VIRGO data.
- As a blip, it would have relatively little energy in the 50Hz-1kHz range
- But I imagine that different algorithms could search for coincident blips in the LIGO/VIRGO data

Future large gravitational wave detectors like eLISA (1 million km arms) would be even less sensitive to short "blips":
- A detector is most sensitive to frequencies whose arm length is about half a wavelength.
- Wavelengths much shorter than the arm length will have multiple cycles in the measurement arm (almost cancelling each other out)
- Wavelengths much longer than the arm length will have only a small part of a cycle in the measurement arm (dropping below the low-frequency response of the detector)

But if aliens had a warp drive, where are they? (Fermi's Paradox)

20

Chemistry / Re: What to catalyses do?

« on: 30/08/2019 10:26:23 »

Do you know what a jig is?  Have you ever had to assemble a collection of the same objects, over and over?

It gets boring and time consuming to assemble the same thing over and over.   SO...we build a jig.

We will place all the components in the jig......then with one operation.......one lever pull or a crank.....and the object is assembled.

The assembly device is called a jig.

A catalyst is a chemical jig.  It "fits" the components.