1

Just Chat! / Re: Theories to start a new world.

« on: Today at 02:23:32 »

Hi.

I had a hard time with this and have not until now contributed. I find it pretty implausible that the means to get to another world is somehow feasible but the means to take significant information along is not.

    Indeed, the old radio show (which @alancalverd states is still running in a modernised form) has some issues that are just never asked about or answered.    In the radio show "Desert Island Discs", you could choose to take some music discs to a desert island that you've become stranded on (following a  ship-wreck), possibly deported to (following some crime you were falsely convicted of), or perhaps you just went there of your own choice because you've had enough of the rat-race etc.    You just don't ask questions like "is there a record player on the island and a small power station that provides a standard British mains electrical socket?"   Instead you just understand that all you're being asked to do is select the music you would most like to have with you on that desert island.

    If it helps, you can assume an alien race has kindly turned up at the last moment and agreed to take you and a few others to another planet.    Then they're going to leave us alone because......  i.d.k. .... stuff about minimal interference with other cultures until we develop our own  FTL  systems.    There is no time to find other people or download everything from a science repositiory.    So it just turns out that the job of taking some science stuff has fallen to you.

I would think skills would be more important than any scientific theory.  Literacy?

     You can assume the few people start with whatever skills they had when they were on earth.   It may be reasonable to assume they can read and may teach this skill to their children.    However, it's fine if you want to take some basic literacy teaching material to ensure that literacy skills are not lost.   That'll be one slot used in the 3 scientific theories you can take.   There's no rigid rules for this game, you get a yellow or red card at the discretion of the umpire.

----------------
    What's more interesting is that your personality can now be put under a microscope because you've made a reply.
You're worried about the fine details and you've spent a lot of time analysing a thing rather than jumping to some action.    In this situation, that possibly means that you end up taking very little because you just run out of time.   In other situations it's a good thing.   For example, you'd make a fair forum moderator in the new world.
     What you've actually ended up recommending can be paraphrased as follows:
1.   You don't have to take many scientific theories.
2.   You just take some facts.   Science will probably develop if evidence and facts can be found and especially if knowledge can be passed down rather than discovered anew in every generation.

     And maybe that'll work better than anything else.   However, you spent too long analysing rather than doing, the best answer award has already been given out and so you get nothing  -  but thanks for your reply.

Best Wishes.

2

New Theories / Re: there is no time dilation between between bodies in relative motion

« on: Yesterday at 12:51:41 »

Hi.

      Your article is well written but it seems to be suggesting a logical connection from one thing to another that actually isn't as obvious as you imply.

    If I've understood what you've said,   you are proposing the following:

I present one simple model. The speeds of light around a mass should be sloped. In relation to a body of mass, the speeds of light are constant at any fixed distance but change in balance fashion in relation to the distance from the mass, c+v inbound and c-v outbound where v is the gravitational escape velocity.

    That seems as if you were considering the speeds of light in a frame of reference where the mass (e.g. a planet) can be taken as being stationary.   For example, we could have the mass at the origin at all times.
    You don't seem to have any experimental evidence that you've presented but there is a general implication that your earlier example involving an elevator provides some motivation for it.

      Unfortunately, your previous elevator example is different:    In that example, it seems as if you would be using a frame of reference where the centre of the elevator is always at the origin,   so that's an accelerated frame.    The nearest equivalent frame for light around the mass would then also be an accelerated frame,  e.g. one that is in free-fall toward the planet rather than always having the planet at the origin.   Moreover, since you talk about increasing the distance from the planet, you couldn't even use just the one frame all the time,   at every new disatnce there is a different gravitational acceleration toward the planet, so the free-fall frame would be different.

      Therefore, the elevator example doesn't really provide the motivation or justification for your proposal that you might have thought.

    To say this a different way:   You have something that will hold in one sort of frame but then you overlook the type of frame it was and tacitly assume it can apply to any old frame we wish.

- - - - - - - - - - -
      Under the mainstream theory of Relativity, the speed of light CAN be different in an accelerated frame of reference.    So your elevator example isn't necessarily wrong.   I'm not saying that your proposal is wrong only that it doesn't follow logically (because you start using different sorts of frames) and you would want some evidence for it.

Best Wishes.

3

Just Chat! / Re: Theories to start a new world.

« on: 08/12/2024 15:11:02 »

Hi.

   That's a nice reply and can have the best answer award.

And of course the learning of new facts and understandings.

    I'm sure you're smart enough to realise that not everything in the forum is the gospel truth.

Best Wishes.

4

Just Chat! / Re: Theories to start a new world.

« on: 08/12/2024 00:00:27 »

Hi.

But a little education as to the limited validity of the question may prevent our new civilisation from collapsing under the acquired filth of religion.

    OK @alancalverd,  I guess that you don't always get to your chosen place of worship (church, temple etc.) right on time every week.    That's ok.
     However, I can't really put the "best answer" on your post because I'd be at risk of offending quite a few people and that may not be completely in-line with the Forum acceptable usage policy.

Do not use insulting, aggressive, or provocative language.
    [  subsection 2 of the A.U.P.      https://www.thenakedscientists.com/forum/index.php?topic=8535.0  ]

    Insulting every religion is something I'm not sure we can do.   However, you've put a lot of time into making replies and responses and in most other respects you would have had the best answer award.   Thank you for your time and well done.   
     I may not be following this thread after today and so there may not be any "best answer" given out.   Thank you to everyone who has made a reply.

Best Wishes.

5

Chemistry / Re: Shrink ray or growth ray, how could they work?

« on: 07/12/2024 17:26:57 »

Hi.

We might substitute other atoms or dopants but this won't merely alter the bulk size of our target, but its chemistry and physics....

    Not necessarily.   
1.   We might surround the atoms that made up the persons body with some small and almost inert particle lattice.  For example, neutrinos seem to have some effect on the relative permittivity of ice when they pass through it and is the basis for some neutrino detection experiments.
   
2.   We just want to change the effective ε somehow and it may very well be that it is changing - all we need to do is wait for the universe to continue evolving.   
     
    This is evidently a light-hearted discussion started by @chiralSPO , so I won't spend time finding peer reviewed and published papers.   Here's a thing that just came to hand:

------------
[Taken from   https://faculty.sites.iastate.edu/tesfatsi/archive/tesfatsi/MFSpears/mfsgravity.paramet.pdf ]

PERMITTIVITY CREATES DARK MATTER AND
AN OLDER UNIVERSE WITH ACCELERATING EXPANSION

Abstract: The purpose of this report is to provide simple answers to the following three
questions by considering the effects of what has been happening over time to one single
property of open space; namely, the permittivity of that space.....

      .....as long as the particles individually have a greater
permittivity than the space around them, the overall space permittivity will decrease with
expansion.....

- - - - - - - - - -

Best Wishes.

6

Chemistry / Re: Shrink ray or growth ray, how could they work?

« on: 07/12/2024 13:31:53 »

Hi.

but the volume occupied by the constituents of an atom is filled by vacuum 0, not d.

    I agree that it would be nice to change nature's   ε₀  for the universe in some local region around the person.   However, that's not something we can easily do and engineers hate it when you ask them to do the impossible.

     What we have a real opportunity to do, is to change the di-electric or pactical ε in the environment around the atoms.
     In the hydrogenic model of semiconductors, it seems that the radius of space occupied by the electron from a donor impurity does behave as if the di-electric ε of the bulk material is being used instead of nature's vaccum  ε₀.  (and also, the efective mass of the electron rather than its natural rest mass).   We've had discussions about this before (nearly a year ago):
    https://www.thenakedscientists.com/forum/index.php?topic=86760.msg722228#msg722228

   Sadly one of the links I gave to a Glasgow university website seems to be down (things change in a year).   Here's a snippet of a lecture course (Solidstate Physics) from the University of Nottingham, United Kingdom that briefly describes how the usual Schrodinger QM model of a Hydrogen atom is modified - just so you know that there really is some precedent here.    Donor impurity atoms do seem to behave as if they're bigger and it is exactly as if the dielectric ε and the effective mass of the electron in the bulk material is being used in the QM model of an atom.

Best Wishes.


     

7

Chemistry / Re: Shrink ray or growth ray, how could they work?

« on: 07/12/2024 01:30:55 »

Hi.

We can use QM equations and just plug in different mass and charge and magnetic properties....

   Yes, I suppose you could just change the physical parameters of space around the person.     Alter the constants like ε₀, the permittivity of space.   Try and do this in a small bubble around the person you're shrinking.   Very roughly it ought to affect all atoms in a similar way.

    The Bohr radius is 

     Increase and decrease ε  and atoms get bigger and smaller.

   So they can eat food and breathe the air around them because anything close to them is affected the same way.   They also don't fall through the floor by being over-dense because the floor becomes affected when their feet are on it.

One way I thought it might be possible would be y changing the mass of the involved particles.

   Actually, you only have to change the effective mass of the electrons and that's not impossible.

Precedent:
    Semiconductor theory.   The extra electron from a donor impurity atom behaves as if that electron is spread out over many hundreds or thousands of atoms in the lattice.   This can be well modelled with the usual QM model of a Hydrogen atom  where ε₀ is replaced by the appropriate ε of the bulk lattice (and the mass of the electron is usually also replaced with the effective mass of the electron in that bulk lattice).

How would you do this?
    That's a practical problem not a theory problem, so.... someone else's problem.   If you were attempting anything like the same idea as we use in semiconductor theory, then you'd actually want to put something extra into the person.   Some small particles that will act like a lattice while all the other atoms the person is made of behave like impurities in that lattice.

Best Wishes.

8

New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 22:30:06 »

Hi.

   I said I would look into the writing by Penrose.   Sorry, that's not going to happen for a while.   We have severe weather warnings where I am.   I won't be getting to a library for a few days.
   If anyone has an online reference I'll check that  (if the phone and internet lines stay up).

Best Wishes.

9

New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 06/12/2024 02:59:23 »

Hi (again),

Sorry, there's been a lot of new posts since I started this one (and some splitting of a forum post, I think).   I'll still start from an old post of @varsigma .

But, why will an object move at c in that direction?

This would be easier if the forum supported LaTeX to write mathematical equations - but I reckon we can get by.

1.   Let's start with special relativity and talking about un-accelerated objects.

2.   An ordinary object, one with mass, has a rest frame which is a perfectly valid co-ordinate system for the world - it's just as good as any other.

3.    In that rest frame, the object is at rest (by definition).   By definition, its 4-position vector is
 (ct, x, y, z)        (reference https://en.wikipedia.org/wiki/Four-vector#Fundamental_four-vectors )
  where x, y, z are fixed (unchanging) with the co-ordinate time t.
   The proper time elapsed for the object is then    c² dτ²  =  c² dt² -  dx²  - dy² - dz²   but there's no changes in the x,y, z components, so we just have dτ = dt.   In words, "the co-ordinate time is identical to the proper time experienced by this object". 
   By definition of the 4-velocity vector we have    d/dτ   of the 4-position vector  is    (c, 0, 0, 0).

4.   So, in the rest frame, the object does indeed have a total magnitude of the 4-vector that is c.    I won't write out the magnitude of that 4-vector but it's the usual Minkowski norm that we would use.   Furthermore, all of this 4-velocity is seen to be in the time component of the 4-velocity.

5.   The 4-velocity is a proper 4-vector.  So it's magnitude, as defined by the Minkowski norm, is invariant under a Lorentz transformation.   [ Reference:   Notes from an MIT course,   https://uspas.fnal.gov/materials/12MSU/Conrad_4vector.pdf  ].    So in any other inertial frame of reference you may choose to use, the object still has a 4-vector of total magnitude c.
     That's the majority of the proof done.

6.    The object we started with was arbitrary.   Which frame of reference we chose to switch to was arbitrary.   So, any object and any reference frame that we chose for some reason (e.g. the observer was stationary in that frame) will still exhibit the property that this object has a 4-velocity with magnitude equal to c.   However, it's also clear that in some frames of reference, the object is not going to be at rest.  Then some of the spatial components of the 4-velocity will not be 0 and the total magnitude of the 4-velocity has been "shared out"  between the time component and the spatial components but the overall magnitude of that 4-velocity remains equal to c.
   
7.   Now we can relax the assumption that the object was un-accelerated if we wish.  It may not have a single inertial rest frame for all time but it will always have an instaneous rest frame we can use at every instance.   That's all we will need.

8.   We can also generalise to GR rather than SR.   In a local enough region, GR is just SR.  We only need a local frame to define something we can call an objects 4-velocity through the spacetime local to it  (rather than some other co-ordinate velocity it may have, which may be quite bizarre and is not required to be of magnitude c).

-------
   That's probably not the explanation you ( @varsigma ) were looking for but it is AN explanation.
I will spend some time digging for the Penrose discussion you suggested, that may take a day.   Penrose is very good at presenting the deeper philosophy and "physics" of a situation.   Meanwhile the above proof is essentially saying stuff the deeper understanding of "the why".  The mathematics says it happens and that's all we need to know and regard as "the why".

- - - - - - - -

From @Halc 's later post:

but speed is defined as spatial change over time, and is not a meaningful concept in spacetime.

   That sort of speed is obtained from a 3-vector and would indeed be much as you describe.   However, the 4-vector velocity is meaningful and could be regarded as an objects movement through 4-dimensional spacetime.
   Minor differences exist, as mentioned.   The 4-velocity is a derivative of the 4-position vector with respect to a differential change in the objects proper time, τ,  not a co-ordinate time, t.   
    Of course,   dt ≡ dτ   when the co-orindates used are obtained from a frame where the object was (spatially) at rest, but in general they are not.   This slight alteration is sufficient to eliminate many of the issues you mentioned  (the speed.... is frame dependent) because we have tied down the frame sufficiently to have a mathematical object, a 4-velocity, that transforms as a tensor.   It turns out that this 4-velocity really will have an invariant magnitude under the Minkowski norm and that magnitude is precisely c.

    I didn't say I like the way that some PopSci articles describe all objects as moving at a speed of c through 4-D spacetime,  I said the opposite a few posts back:   

I don't especially like this way of looking at how objects move, there's a lot that would need some more precise mathematical formulation.

    It can be properly formulated in Mathematics and can be used - but most PopSci articles will just allow a reader to imagine a 4-velocity as if it is just a Newtonian 3-velocity in the 3 spatial components with an extra and naively imagined time-like velocity component bolted on.

Best Wishes.

10

New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 05/12/2024 22:17:16 »

Hi.

"c" has units of m/s and time has units of s, how can one have a speed(m/s) in a dimension of s?

    If you skip all the details, as is often done in PopSci,  it's summarised like this:

If you use a conversion factor c to convert the proper time elapsed to a space equivalent, then.....

   A more rigorous mathematical formulation would require us to be careful about defining 4-vectors and not simply treat them as if they are just ordinary Newtonian 3-velocties with a 4th time-like component strapped on.   For example, we would specify an objects position 4-vector as   (ct, x, y, z)   rather than (t, x, y, z).   That decision alone means that the time co-ordinate for an objects 4-position has units of  metres not seconds.  Next, we would also define the velocity 4-vectors  as a derivative w.r.t. proper time,  d/dτ  of the 4-position vector,   instead of using co-ordinate time t as in newtonian mechanics where the 3-velocity is just d/dt of the Newtonian position 3-vector.  [Reference:   https://en.wikipedia.org/wiki/Four-vector#Fundamental_four-vectors ]
    Note that the last decision makes very little difference at low speeds,   the proper time elapsed for an object is almost exactly the same as the co-ordinate time elpased.   So, it's not too criminal to allow a reader to imagine that a 4-velocity has 3 spatial components which are just the ordinary Newtonian 3-velocity with a 4th component, a velocity in the time direction, strapped on as an extra.   In truth the 3 spatial components of the 4-velocity are not quite the same as the Newtonian 3-velocity and that will become more apparent at higher speeds.
    Anyway, with a proper consideration of 4-vectors we can make all the ideas more rigorous and there is no conflict in the units of measurement for the time component or spatial components of the 4-velocity.
    It is really only the formal 4-velocity of an object that must always have a magnitude of c and it's convenient that the 3 spatial components are a bit like the ordinary Newtonian 3-velocity of the object.

- - - - - - - -

Have you seen Penrose's description of two observers walking past each other?

    I'm not sure that I have, sorry.   Is there any online reference?
I can hazard a guess as to what it was about.

Best Wishes.

11

New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 05/12/2024 12:58:29 »

Hi.

In a universe with four dimensions, you have to move at the speed of light in at least one of them.

    A blunt response would be just to say "No, that's not quite right".   I would have preferred to make a softer response but the reply is going to get too long and too awkward to understand if I do that.

     The more common way of thinking about movement through 4-d spacetime is as follows:
1.    An object always moves with a velocity of magnitude c.   Not "at least" c, always precsely c.
2.    You can share that out between some velocity in the spatial directions and some in the time direction as you wish.

     Examples:    If an object has zero ordinary 3-D spatial velocity, then it advances in the time direction as much as possible.   Proper time for that object advances exactly the same as the co-ordinate time you were using (the thing we used to declare that the object had 0 spatial velocity).  If you use a conversion factor c to convert the proper time elapsed to a space equivalent, then advancing 1 second of proper time per 1 second of co-ordinate time becomes something we can say is a velocity that the object has of   c  metres per second  (instead of  1 proper second per co-ordinate second).
    However, if it has some ordinary 3-D spatial velocity, then the proper time for that object advances more slowly than the co-ordinate time, this is known as "time dialtion".   Conceptually, you have used up some of its light speed velocity in the spatial velocity and so there is less of it left available for advancing into the time direction.    In the most extreme case, a particle of light moves with a 3-D spatial velocity of c, so there is nothing left at all for advancing in the time direction and the proper time for that light particle can never change regardless of how much the co-ordinate time may change.

     I don't especially like this way of looking at how objects move, there's a lot that would need some more precise mathematical formulation.    None the less, it provides some general understanding if we just skip all the details and this is often done in PopSci where this concept of objects always moving at c is used.

    So, I could have taken a softer response approach as follows:   
You said:
   In a universe with four dimensions, you have to move at the speed of light in at least one of them.
As a minimum the words "at least" have to be striked out.    It would be better if we replace the entire sentence with something like this:
   There's nothing special about what we identify as the x,y, z axis of space and the t or time axis.  We can always construct a "direction" of travel for an object that is a combination of the spatial and time directions.   An object will then always move at precisely c in that "direction" and have no velocity at all in the other three directions orthogonal to this.

Best Wishes.

12

Just Chat! / Re: Theories to start a new world.

« on: 04/12/2024 01:10:41 »

Hi.

....we must either find some means of preventing people from asking meaningless questions, ...

    You can't and probably shouldn't even try to censor peoples thoughts or prevent them from asking questions.   However, that's some issue you could read about in a Dystopian novel or else move to a country that doesn't allow such novels if you want to experience something similiar to it in practice.

   None-the-less, thank you for your time and responses, @alancalverd .   Your views are valid and .... left uncensored.

   I've re-read one of your earlier replies and decided that including the atomic theory of chemistry may be some attempt to help a new society get past some of the bigger problems that were faced by science.   For example, perhaps someone would feel that the most important theories to take are the ones that seemed to have been the biggest hurdles for our society and has the greatest risk of de-railing or slowing the development of science if we didn't have it.   With your example, that might be allowing a society to by-pass alchemy and get straight to something resembling modern chemistry.

Best Wishes.

13

Geek Speak / Re: What is 'maths'?

« on: 03/12/2024 00:23:32 »

Hi.

But, yeah,  time is linear.

    I'm sorry, I'm not sure what that means.   Time varies linearly with the number of seconds that have passed rather than having some quadratic dependence?   Time is an operator that is linear - time acts on one girl to make an old lady,  so it acts on  λ girls to make λ old ladies?   I suppose all those things are true of time.

    A quick perusual of the web suggests people say "time is linear" when they mean one or both of the following:
1.  It's uni-directional.  You can't go backwards.
2.  It has some beginning and some end with all things in between being conceptualised as a line rather than something else like a complicated branching structure or a fuzzy cloud of stuff.   So all events are totally ordered.  Specifically given any two events we could always say one event is "before" the other.

then what is measurement?

   An excellent question but not one with a short answer.   It probably needs its own forum thread.
It's a contentious issue in Quantum mechanics which I'm sure you're aware of.

Best Wishes.

14

Just Chat! / Re: Theories to start a new world.

« on: 02/12/2024 22:58:48 »

Hi.

Religion is all about selling undisprovable hypotheses in order to control people's actions.

   No, that just sounds like human selfishness, corruption and some desire for power by a few people who have come to be in charge of the religion or else in charge of something else and just citing religion as supporting them.    Religion is about not wanting to be alone, left feeling pointless, worried about not existing any longer, seeking the answers to fundamental questions  etc. etc.   Things that you aren't going to make disappear just by not bringing any religion to the new world.
   c.f.   @paul cotter  's reply.
- - - - - - - - - -

I think you meant "non physics" science rather than "non physical" science.

    Physical sciences involve studying the inanimate stuff while Biological science is the study of the animate (living) stuff.   There's definitions on the web and it's reasonable to split science into these two broad categories.   I think I can say non-physical sciences and just hope people understood I meant Biological sciences rather than the study of nonsense with no physical basis.

- - - - - - - - -

It must be useful there and then

    Thanks for your time and response.   It's good and perfectly understandable.   It does have some comedy but is otherwise similar to the response first given by @paul cotter so probably won't get the best answer award.....  Which really doesn't matter anyway and would not change your life.

Best Wishes.

15

Geek Speak / Re: What is 'maths'?

« on: 01/12/2024 23:14:54 »

Hi.

But then mathematical truth is something that again presumably, has always been true.

    Well maybe.

    There are problems proving that any system of Mathematics (which must inlcude some basic arithmetic) is consistent.
   See    https://en.wikipedia.org/wiki/G%C3%B6del%27s_incompleteness_theorems#Second_incompleteness_theorem
 or more generally,  Godel's first and second incompleteness theorems.

    It may be consistent but we can't prove it.   This undermines the pedestal on which Mathematics is often put.   So the example you gave, Pythagoras' theorem, fortunately is something we can prove from the axioms and would seem to be true by any reasonable judgment.   However, it's also true and provably true in an axiomatic system where we have just deliberately added Pythagoras' Theorem as one of the axioms and arbitrarily knocked out some of the other axioms.   There doesn't seem to be an objective axiomatic system that we can have and also KNOW that this system will be consistent.   
      It's true that cheese can fly in a system where I say that it can, that's just not a very good system to use and any system that inlcudes that axiom could quickly become demonstrably inconsistent.   Mathematical truth is something you can give any statement if you just start with that statement as an axiom -  so it's worth nothing. 
      What we would want to use is a system that is consistent.  So what you probably mean by "mathematical truth" is that the statement is true under the systems of mathematics that we do commonly use.   We hope that our preferred systems of Mathematics have intrinsic validity and integrity such as "consistency" - but we will never know.
      I do not know if Pythagoras' theorem is true now, was true or has always been true in any absolute sense.   I only know that it is true now and would always have been true in the axiom systems that we do commonly use, for whatever good that axiom system may be.

Best Wishes.

16

Just Chat! / Re: Theories to start a new world.

« on: 01/12/2024 20:55:22 »

Hi.

    So far, I'd say @alancalverd is more likely to get the best answer award and 2 people is about half of the entire forum.

Why is the later reply better?   
1.    Some thought has been put into how your choices may shape the new society.
2.    Some consideration of non-physical sciences like Biology has been made even though the original question used the therm "theory" and nearly everything with that name belongs to the physical sciences.

Counter-arguments:
1.     People are getting more insight into how to respond with each previous reply.
2.     I'm not sure I can endorse a statement that opposes all religions.   Moreover, isn't it likely that a society left in that position starts its own religious beliefs anyway?   Aren't you leaving science at risk of becoming a religion?

.... and probably the Krebs cycle if I'm not allowed the whole biochemistry library. Then my descendants would understand how we got here...

    They are likely to believe  "this is how it was"  rather than "this is some attempt at explaining things and most certainly not exempt from future examination and adjustment".

What might be left to do for anyone wanting that coveted "best answer" award?
     It's up to you to come up with ideas.   Here's a couple of things you could try but I'm sure you can find something else.

1.  You might try writing something with a bit of comedy, however I won't too favourably on anything that's just comedy.
2.   You might go strongly in an unusual direction and be able to argue for it.   For example, perhaps we would better off not taking ANY of the old science theories forward into the new world.

Best Wishes.

17

Just Chat! / Re: Theories to start a new world.

« on: 30/11/2024 17:42:46 »

Hi.

Optics seems an unsual choice.
   Overall, it all seems like something I would have expected you to choose and say.
You seem to be choosing on the basis of what will be useful to do practical stuff on the short term.   Your personality profile is that of an engineer based on this task.
   

More advanced theories.... when the basics have been taken care of.

    You're biased toward the view that science will emerge from the need to solve practical problems.

Best Wishes.

18

Just Chat! / Theories to start a new world.

« on: 30/11/2024 15:26:16 »

Hi.

    So, in Britain a few years ago there was a radio show where someone chooses the three music discs that they would take with them to play if they became stranded on a desert island, that was called "Desert Island Discs".

     Let's do a science version of that.   Moreover, why doesn't the TNS radio show do a version of this? 

     Due to some problem, civilisation is leaving earth and will try to colonise some other planet and start a new world.   You can take the material that describes three theories in science.   Which three theories would you choose to take?


    Thinking time allowed:   I don't mind but 5 minutes is adequate, it's fun not something that is happening.   Yes, you will be critically judged based on your answers but it's better than doing some personality quiz.   I may give out the prestigious award of a "thankyou" mark for the first few answers and possibly the more prestigious award of a "best answer".   Then again, I may not but instead just thoroughly deride the response you make.   Life must have some risk.

Best Wishes.   

19

Question of the Week / Re: QotW - 24.12.06 - How long does it take a galaxy to form?

« on: 29/11/2024 20:20:02 »

Ummm... what's happened to the dates here, why was this at the top of the board?  The dates for several of the posts in this board and their order of appearance seems odd.

20

Question of the Week / Re: QotW - 24.12.06 - How long does it take a galaxy to form?

« on: 29/11/2024 11:20:03 »

Hi.

The evolution of the universe in diagrammatic form:



Here's the important information:

1.    The bit on the far left we will call the Big Bang and identify as time = 0.

2.     The time that we're using is known as cosmological time or time derived from the FLRW metric.   It's how a clock would progress if we were co-moving with the general expansion of the universe.

3.     ....At some point around 200 to 500 million years (after the Big Bang), the earliest generations of stars and galaxies form (exact timings are still being researched),......

4.     .... While early stars have not been observed, galaxies have been observed from 329 million years since the Big Bang, with JADES-GS-z13-0 which the James Webb Space Telescope observed with a redshift of z=13.2, from 13.4 billion years ago.....

5.     Some changes and hence what we can call evolution of a galaxy continues right upto today.    For example, there are galaxy merger events, material falling into black holes, some stars being thrown out of a galaxy  etc.      So we could say that galaxy formation started about half-a-billion years after the BB and continues to now (about 13.8 billion years after the BB).

6.     More information including all the quotations and diagrams above are available at   https://en.wikipedia.org/wiki/Chronology_of_the_universe.

7.      As it happens, there's a fairly recent discussion on another forum you may also wish to see.   
https://www.physicsforums.com/threads/approximately-how-long-does-it-take-for-a-galaxy-to-form.1063803/
      They were suggesting  1 billion to 14 billion years.    The significant difference here (in this forum post and the info from Wiki) is that galaxy formation is suggested to have started half-a-billion years earlier than that.     

8.     There are some  hypothetical or "what if" situations that you might wish to consider.    In the evolution of the unverse that is discussed above, there weren't any atoms around until quite a while after the big bang, so no chance for stars to form.    You could be asking how long a galaxy takes to form provided there is hydrogen gas scattered around and we are just waiting for this to amalgamate into stars and galaxies.   You could estimate this by subtracting a suitable early time for the universe from the times mentioned above.

Best Wishes.