481

Just Chat! / Re: Mathematics is a decent science.

« on: 17/06/2021 13:04:00 »

Let's say Jane went shopping and picked up a thing that required her to evaluate an integral over a closed path on the complex plane.  Alternatively consider John, who was out walking in the sunshine when he had a need to generate an infinite sequence of numbers that are co-prime but not primes.    Where are these people going to get help with their serious problems?

Well, they could just sign up to a math forum.

482

Just Chat! / Re: Mathematics is a decent science.

« on: 17/06/2021 11:11:41 »

The principal language of science is mathematics. If this were a cricket forum, you wouldn't expect it to have a section on  English.

John and Jane do indeed have serious problems, but I don't know where to look for clinical guidance. Georg Cantor never really recovered.

483

Physics, Astronomy & Cosmology / Re: If a BH singularity defies our mathematics does it also defy our physics?

« on: 17/06/2021 09:16:33 »

We could mention that Einstein found the idea of BH rather intimidating. He went from questioning their existence to accepting, and as I seem to remember, doing it on several occasions, before finally accepting it.

484

Just Chat! / Re: Mathematics is a decent science.

« on: 17/06/2021 09:07:35 »

Probably because most of us aren't that advanced when it come to mathematics ES. But yes, I agree in that it could be one of TNS offerings. Although when mathematics is needed it usually will get used here too. If you use it though it should be a priority to be very clear about what your symbols indicate, and how to read it/you. For much the same reasons.

485

Just Chat! / Re: Mathematics is a decent science.

« on: 17/06/2021 00:32:25 »

Hi.

   Why do you (Nakedscientists) have a thousand sections for life sciences (that was just a rough count) and not one section for Mathematics?  Mathematics is everywhere but life sciences are only useful in a small number of real world situations.
   Let's say Jane went shopping and picked up a thing that required her to evaluate an integral over a closed path on the complex plane.  Alternatively consider John, who was out walking in the sunshine when he had a need to generate an infinite sequence of numbers that are co-prime but not primes.    Where are these people going to get help with their serious problems?

General maths is not a science, unlike economics or statistics which is a way of interpreting data through maths.

486

Physics, Astronomy & Cosmology / Re: Is everything in the universe in motion?

« on: 14/06/2021 21:12:23 »

OK, I know what you mean by geodesically complete now. I think that mathematically one can see CMB radiation in the direction of a black hole. The thing formed at some point, and a steady stream of CMB light was suddenly severed, but the trailing end of it is still coming at us, just like you never stop seeing a light dropped into a black hole. From a distance, yes, it is insanely redshifted, but it's there. Just food for thought. Not suggesting that means there's isotropy in any frame. If I look at the CMB in the direction of a distant black hole, I will very much notice the distortion there regardless of my motion. The CMB will not be isotropic.

However A FRW universe is NOT one with lumps in it,  it is one where there is a homogeneous cosmological fluid.

So the standard model is wrong because it disallows rocks? I would say it simply doesn't attempt to describe local details.

Halc was unduly concerned that a CMB frame allows for some universal ordering of all events throughout the universe.

That wasn't my concern at all. My observation was that no known coordinate system orders all events, covering both large scale (events outside our event horizon) and local variations (lumps as you put it). This seems to be a problem in need of solving by any metaphysical assertion of there being a preferred ordering of events. It is of no actual concern to me because I propose no such metaphysical premise.

Any co-ordinate system specifies events with co-ordinates and (as Halc implied) you can choose to look at the time co-ordinate as a number and order the events according to that number, if you wish.

Not any coordinate system. One one that defines a coordinate to both events being compared.

There's no reason why you should do this

Totally agree, but not everybody does. I'm currently conversing with someone who very much cannot even conceive of a universe where there isn't a co-ordinate system that is truthful to the exclusion of all others.

the existence of the CMB frame is interesting but it doesn't break special relativity.

SR is a local theory, so the CMB is irrelevant to it. If SR is to be applied to the universe as a whole (as occurs if one approaches the zero-energy-density limit of the FLRW model), then one prediction that follows is a lack of CMB. Hence the demise of the Milne solution which proposed just that: SR for large scales and GR only for local variances.

I have no doubt that students of special relativity were taught that SR prevents us from identifying one inertial reference as being preferred over another

Only in Minkowskian spacetime, and the universe at large scales is apparently not Minkowskian. So all one needs to do is a non-local test.

487

Physics, Astronomy & Cosmology / Re: Is everything in the universe in motion?

« on: 12/06/2021 14:59:31 »

Hi Yor_on.   I hope you are well.

  Yes, the CMBR is observer dependant.  There will be a dipole in the frequencies of e-m radiation observed according to the motion of the observer.
    Easy reference:   https://astronomy.swin.edu.au/cosmos/c/Cosmic+Microwave+Background+Dipole.

   The CMB frame is an inertial frame where the dipole disappears.

Late editing   Obviously no one has actually travelled to another group of galaxies or moved a bank of microwave receivers at relativistic speeds to see how that affects the dipole.  The earlier discussion(s) refer to what our models suggest and the main empirical evidence we have for this is that the real observations from our part of the universe are consistent with it.

:) Np ES, it's a pleasure reading you. And if we consider 'relative motion' we can test it at different locations in space and time. Just by staying on earth, or in its vicinity.

488

Physics, Astronomy & Cosmology / Re: In deriving the Rocket Equation, why does this segment seem to be added twice?

« on: 12/06/2021 01:09:41 »

Hi @cmiles0509

You said:

In deriving the rocket equation, we go through this step:
mv = (m-Δm)(v+Δv)

   Which is not true and isn't mathematically correct.

The derivation you are looking at uses the principle of conservation of momentum.  This applies to the TOTAL (or sum of all) momentum in the entire system.   It does not apply to the rocket on it's own.

Before burning a unit of fuel,   the entire system was just the rocket with mass m and velocity v.   So the total momentum was just  mv.
After burning the unit of fuel, the system is more than just the rocket.  It is the rocket  PLUS  the expelled gas (fluid).  We tend to put both liquids and gases under the general name  "fluids".

We have:         Initial   Momentum     =         Final  Momentum
                              mv                       =      momentum of rocket   +  momentum of expelled gas

This effectively jumps straight to the second equation you stated:
mv =     (m-Δm)(v+Δv)     +          Δm(v-u)
on the right hand side, the bit in italics   is the momentum of the expelled fluid.  The first term (not in italics) is the momentum of the rocket (with the new mass of m-Δm    and new velocity  v+Δv ).

Does that make some sense?

Ahhhhhh, so that means that the equation (in its entirety) is referring to "All the momentum that is occurring between the fuel and the rocket"?

And, if I understand correctly, by "isn't true and is mathematically incorrect", you mean that the first part of the equation I put (which excluded exhaust velocity and all that) was incorrect (since it was incomplete)? Therefore the second section is, in fact, correct?

That's a little harder then, why does the equation account for the momentum of both fuel AND rocket, if the fuel's momentum doesn't really matter once it has been used to propel the spacecraft? I need to look into this further!!

489

Physics, Astronomy & Cosmology / Re: Is everything in the universe in motion?

« on: 10/06/2021 10:53:31 »

So the CBR (CMB) is observer dependent? Makes sense to me, if that is what you're suggesting ES.

490

Famous Scientists, Doctors and Inventors / Re: Who is the father of physics?

« on: 07/06/2021 11:38:13 »

sanu asked the Naked Scientists:
   
Who is the father of physics?
What do you think?

@sanu

IMHO This Question is a tad bit Illogical.
👎
It makes ZERO sense.
0
Rather, it promotes negative segregation, & also seeds possible futile debates.
🌵
It's Almost like entering a Synagogue, a Church & a Mosque & asking Who is the Real God!
🦧
Wish the Science Community at large Stops promoting & starts ignoring such ludicrous questions.
🙅

P.S. -

IMG_20210607_161225.jpg (186.78 kB . 701x1051 - viewed 11161 times)

491

Physics, Astronomy & Cosmology / Re: What would happen if every neutron on Earth disappeared?

« on: 04/06/2021 20:26:44 »

I'm still uncertain if there should be reason why the neutrons would be considered to be associated with the sun

Technically, the wave function of any given particle occupies all of space, including beyond the Andromeda galaxy. So it can be considered to be "associated" with everything. The probability distribution is infinitesimal at such an immense distance, however, and thus the probability of tunneling to such a distance is also beyond miniscule.

I'm pretty sure that the Earth spontaneously exploding from such a hypothetical mass neutron tunneling event would very much count as an observation if we happened to be here when it happened. So any requirement for it to be observed is fulfilled.

492

Question of the Week / Re: QotW - 21.03.02 - Difference between rechargeable and normal batteries?

« on: 03/06/2021 23:31:14 »

The lower internal impedance of rechargeables is particularly important for power tools as it allows higher stall current and torque than can be achieved with the same size primary cell. Used with a "joule thief" inverter, you can also turn more of the theoretical stored energy into useful energy at constant voltage. 

Most primary cells can be recharged a few times by adding a bit of AC ripple to the charging voltage. It's a black art that has largely been superseded by efficient rechargeables but various gadgets for maintaining primary batteries were popular in the 1970s because 4 x 1.5V cells was cheaper, lighter and had better energy density and less standby leakage than 5 x 1.2 V NiCads in a walkie-talkie. 

493

Plant Sciences, Zoology & Evolution / Re: How can I keep my grass short?

« on: 01/06/2021 00:19:06 »

Rabbits are less messy than cows and don't completely destroy the lawn, but I would recommend a radically different approach - mental mowing.

The Boss sees it as an unending chore, fighting back the inevitable green tsunami which was there before us and will not just outlive us but even use us as nutrient as it grows on our graves, so what is the bloody point.....

I on the other hand imagine that I am preparing Twickenham, Wembley, Wimbledon, St Andrews or Lord's (depending on the length of the cut). Who knows, with a bit of practice I might even be talent-spotted and get to do that final cut cheered on by an expectant crowd.... On a dry winter night I might creep out and make a runway for SoE to insert another agent - it's even more fun to mow in the dark!

If you don't enjoy sport or have a taste for guerrilla warfare, sprinkle the grass with gin, so it comes up "half cut".

494

Plant Sciences, Zoology & Evolution / Re: How can I keep my grass short?

« on: 31/05/2021 21:12:23 »

Getting a slow growing/dwarf breed definitely helps.
I have many kinds of grass, and I need to mow when the fast growing stuff gets long, or if the weeds outrun the grass.
I have moss taking over the shadier areas, but any abuse scrapes it away leaving bare dirt. It doesn't dig in with roots. Moss is soft and nice to walk on.

Another idea: Get a cow. Cows keeps the grass trim without killing it. Sheep/goats tend to eat right down to the roots so you need to herd them around to prevent them from killing off the grass in one area.

I've reduced my mowing area by letting certain 'weeds' grow. I have violets and clover all over, which never get really tall. I have wild daisies that have taken over big swaths, covering the lawn with over a 1000 labor-free flowers each season. They're just beginning to bloom now.

495

Plant Sciences, Zoology & Evolution / Re: How can I keep my grass short?

« on: 31/05/2021 20:25:09 »

Astroturf.

You can often buy it cheap when local stadiums remodel.

496

Plant Sciences, Zoology & Evolution / Re: How can I keep my grass short?

« on: 31/05/2021 18:32:22 »

The south side of my lawn started sprouting moss after the neighbour put up a six foot fence blocking most of the sunlight. After a few years it's now a thick carpet of moss with a few sparse wisps of grass poking through it.

497

Geek Speak / Re: Do we have enough safeguards for the advancement of science?

« on: 30/05/2021 19:33:55 »

P.S. -

94ce4fdbab376a73b5fecb812f7da5e0.jpg (79.42 kB . 564x789 - viewed 17921 times)

498

Just Chat! / Re: What is the Fastest Accelerating Species on planet Earth?

« on: 27/05/2021 20:49:35 »

Hi Zero,  I hope all is well.
Do we have to wait for the poll to close?

!!!Greetings!!! @Eternal Student
😊
🙏
Hello there, & Welcome to the TNS Forum.
🙋

Yes I'm doing just Fine, Thank You for asking.
Hope you are keeping well & in good company too.
🤞

(When you type in any registered users name, say for example ' Halc ' they would read it when they visit the ' OP '.
But say if it was something of Grave Importance or an Emergency situation...
Then simply attach the ' @ ' sign before their name..
@Halc
(Like 👆 this)

Then a special email notification would be sent to the User stating...
" So n so mentioned your nickname in so n so OP ".
(I did that with your Nickname... @Eternal Student & perhaps you've been Notified thru email. )
Simple!
👍

Now coming onto your Query.
I had eventually chosen an Option to " Show Poll Current Results as soon as User Votes "... Hence, perhaps the Poll does in a way self reveal as time passes & more Users vote, then Percentages change.
👍

But You know what, this place is stuffed with Smart, Intelligent & Wise folks...
😏
Hence the moment i Create a Poll...some SmartyPants instantly crawls in & blows it up!
😑
At times I'm forced to Wonder, where the Heck in the World are all the dumb folks hiding at.
🤷
& What's more...at times... I'm even challenged bout my Own Correct Option Answer.
☹️
Seriously, this place is pretty hard to survive in.
😔

But Hey!
👻
I'm still Alive n kickin!



P.S. - You are a NewBee, still pretty sure You read all those looong & booooring Terms & Conditions & Rules & Regulations, Right?

But how'd You cope up with that specific rule which states :-
 " Users need to be Naked while Reading or Writing anything in the Forum " ?
🤔
Honestly, that was a deal breaker for Mee...but somehow I've got used to it now.
Perhaps You would too.
👍


First Edit - This is how i selected Your Quote & then replied to it.

I went on your Comment & Clicked on the Blue ' Actions ' Tab.


Screenshot_2021-05-28-01-26-52-887_com.android.chrome.jpg (196.59 kB . 1080x2156 - viewed 17031 times)

Choose the very last option ' Quote (Selected) '.

I've Noticed You personally Thanking Users, which is s Really Good thing.
👍
But if you like you could also just simply go to their Comment & click the Blue ' Actions ' tab & choose the very first option...
' Say Thanks '.
(I'm gonna do it with your Comment/Post)
👍

Second Edit - Once you Thank a User's Comment/Post...this is what appears at the Bottom.


Screenshot_2021-05-28-01-36-34-205_com.android.chrome.jpg (230.19 kB . 1080x2156 - viewed 17101 times)

' The following Users thanked this post : Zer0 (my nickname)
👍

Third Edit - Seems you're easy fit with the LaTeX & already aware of how to create an OP n how to comment n everything.

But if You wish to Create your Own Funn Poll...just enter any sub-section...like the one this Poll is in
 ' Just Chat ' & simply click on the Bar Statistics Option.


IMG_20210528_012515.jpg (242.7 kB . 1080x2156 - viewed 17097 times)

Once you do, the Poll methodology is pretty easy to Understand n self explanatory.
👍
Just Please make sure to add the
 " ? " Sign at the end of each of your OP.

Fourth Edit - Wondering how I'm
 ' Editing '  my own post, after I've already posted it?

Say if i make a comment, but forget to add a minor detail, or say after i post it n read it(maybe at times the
 ' Preview ' option might Not work) then i could still ' Modify ' my own post to make Corrections or add missing details.


Screenshot_2021-05-28-01-47-28-848_com.android.chrome.jpg (207.11 kB . 1080x2156 - viewed 17093 times)

Third option is ' Modify '
& Incase i wanna dump my whole post thinking it's invalid, then Fourth option ' Remove '.
👍

Fifth edit - Yes I'm inserting Screenshots into my post.

Whenever you're typing into your post, right at the bottom you'd see...


Screenshot_2021-05-28-01-53-57-071_com.android.chrome.jpg (339.42 kB . 1080x2156 - viewed 17079 times)

+ ' Attachment and other options '

Click on the ' + ' (plus) sign & you'd get further options...


Screenshot_2021-05-28-01-54-30-764_com.android.chrome.jpg (363.73 kB . 1080x2156 - viewed 17080 times)

I first click on ' Choose File ' & then select the appropriate image from my screenshots & after that i return to the Post n click within it to mark the Spot where I'd like to have the image shown(your cursor position would be the spot) & then again i scroll down to 'Attachment Options & finally click on
 ' Insert Attachment '.
👍


& Once again, on behalf of All of US, Welcome!
Hope You have a Wonderful Time in here, nJoY!
🖖
(Mods out here are extremely helpful, do Not hesitate to ask for Help...& Remember, You are Alot Smarter than You Think.)




Sixth Damned Edit - See, i forgot to mention i login thru an Android device(cell/mobil) hence my screenshots would differ from the Desktop Version...but won't be that different or difficult to Understand.
Okay Cheers Now!
🍼

499

Physics, Astronomy & Cosmology / Re: Would altering the moon's weight change its orbit?

« on: 26/05/2021 14:58:04 »

The tidal distortion (bulges on both sides of the earth nearest and furthest away from the moon) is what's important for the recession of the moon.   The oblate-ness of the earth due to it's rotation is a more permanent bulge around the equator, which is interesting but nothing to do with why the moon is receding?

I wouldn't go so far as to say 'nothing to do'. They're both effects of Earth's spin.  The spin causes the oblate shape. The angular momentum of Earth's spin is what is being transferred to the lunar orbit. Some energy as well, but most of that energy is lost as heat.

Returning to the main topic,  the tidal effects from the moon would seem to generally increase if the moon did come closer to the earth (with the moon having much the same mass).

Yes. The moon was much closer in the past, and the day was perhaps 10 hours long like it is on Jupiter. The tides (assuming oceans of the same volume as today) would be much higher.

Which would then tend to oppose progress toward the earth and encourage recession.  Unless the mining operations on the moon are astonishingly rapid, this may help to prevent the moon spiraling into the earth.

That all depends on what forces are put on what's left of the moon. If you keep the system closed (no mass is allowed to leave the system), then mining the moon would probably send it into higher orbit. It isn't going to crash into Earth.
On the other hand, eventually the moon will reach a maximum altitude and cease this recession. At that point it will begin to spiral in very slowly as energy is drained away by solar tides. The day will eventually become very short again and the moon will impact Earth, all without any mining help. Of course, before this happens, the sun will turn into a red giant and probably (not definitely) swallow both, so the above is assuming the sun is immortal. It also assumes the moon will not break up, which in fact it will. Earth will get a nice set of rings to make Saturn jealous.

However, maybe most of the energy lost would be noticed in the reduction of earth's rate of rotation.

Left alone, the day will eventually max out around 1500 hours before it begins to shorten again. The moon will appear quite small (no total eclipses anymore) and permanently in one spot in the sky for the half of Earth that can see it.

500

Physics, Astronomy & Cosmology / Re: Can we communicate with civilisation in anti matter solar systems

« on: 25/05/2021 13:53:54 »

Hi.
I've got to agree with evan_au.
But I'd be interested in knowing where you (yairdoza) got the original information -

Recently I read that there might be up to 14 solar systems in our galaxy that are made out of anti-matter.

  Any chance of finding out where you read that?  Does it start with   Wik  and end with  edia ?

I read it in New Scientist from 1st May 2021 page 16