1

General Science / Re: What is Energy? Like, seriously, what is it?

« on: Yesterday at 21:47:17 »

Hi.

@Just thinking
   Your last post is profound.   There are a great many scientists that now think energy should be divided into two types:   Kinetic   and   Potential   and that is all.    Furthermore, potential is just the ability (the potential) to provide the other form of energy.  So they would say there is only one genuinely observable form of energy - Kinetic, the energy of movement.

Best Wishes.

2

Physics, Astronomy & Cosmology / Re: Does gravitational time dilation/GTD really cause gravity?

« on: Yesterday at 02:03:27 »

Hi.

In any quantum gravity field theory the graviton would be an elementary particle that mediates the force of gravitational interaction. As @Halc says it's not often used in this way. probably because the theory has real problems at the moment.

    Agreed.   When it is used it's used this way:

Upon qunatization, Einsteins equation predicts spin-two particles called gravitons.  We don't know how to carry out such a quantization consistently, but the existence of gravitons is sufficiently robust that it is expected to be a feature of any well-defined scheme      [Fig. 4.2 and text,  p. 167,  Introduction to Spacetime and Geometry,  Sean Carroll]

As you know QED treats photons as particles that carry or mediate the electromagnetic force. In this model charged particles interact by emitting and absorbing photons, but these photons don't experience the electromagnetic force themselves, and so they do not interact with each other, but the effects of electromagnetism are produced by the energy and momentum they carry. The photons that carry force are known as virtual particles in QED and are shown as internal interactions in the Feynman diagrams and basically are there to make the energy equations add up

    The analagous Feynmann diagrams with gravitons look like this:

Feynman.JPG (27.32 kB . 742x228 - viewed 139 times)
    The vertical swirls are virtual gravitons.  The diagram on the left shows two electrons interacting, the one on the right shows a graviton interacting with another graviton by exchanging a virtual graviton.

Clearly, the graviton would have to fit a similar model, but I wonder what would take the place of charged particle interactions when, as @Halc says, the gravitational wave causes a disturbance in spacetime. We would certainly see that as a movement of test particles (as a distant observer)and in a Newtonian system would describe it as a force. Also, that movement (oscillation) of the test particles is not in the direction of the wave propagation, so nothing is being pulled towards the source, but it is similar to light exerting an effect on electrons in the photoelectric effect. Does GR give a clue? This isn’t an area I’ve looked into.

    See above.  Note that there aren't any consistent quantum theories of gravity that I am aware of.  The general properties are based on ....  well, in my case, whatever Sean Caroll was basing it on.
    There are some important features that would seem to be present in the scheme:
    Electromagnetism is mediated by virtual photons which only couple to (electrically) charged particles and, as you (Colin2B) said earlier, photons do not couple to each other and exchange a virtual photon - so they don't experience an electromagnetic force.  As far as the gravity is concerned, anything with energy-momentum is a charge.  Since gravity couples to energy-momentum, gravitons should interact with every kind of particle, including other gravitons. 
[reference: p.166-167,  Spacetime and Geometry]
    The interaction of gravitons with other gravitons is supported by the non-linear nature of the Einstein Field Equations.  A solution involving two masses as a source of gravitation is not the sum or superposition of the solutions for each mass individually.   This is completely different to anything in electrodynamics.

     The discussion of gravitons in Chapter 4 is not based around gravitational waves, actually gravitational waves aren't even mentioned anywhere in that chapter.  Carroll describes the virtual graviton quite directly as a quantised perturbation of the metric and is discussing the ability for the exchange of a virtual graviton to deflect the path of two particles that approach each other.

     You (Colin2B), Halc and most others (including myself) have generally referred to gravity as a geometric effect rather than any force.  Gravitons do not naturally fall out from classical GR and you are correct that LIGO has not been detecting any forces towards or away from any sources but just a disturbance in the metric.
    Section 4.7 on p. 177-181,  Spacetime and Geometry seems most relevant here:
In practice, it is common to invoke the equivalence principle to justify any of the following four ideas:
  1. ... (usual stuff)...
  2. There exists a metric on spacetime, the curvature of which we interpret as gravity.
  3. There do not exist any other fields that resemble gravity.
  4. The interactions of matter fields to curvature are minimal: they do not involve direct couplings to the Riemann tensor or its contractions.
 .........
   Which is enough to suggest that any quantum field theory for gravity would be unlike anything else you've seen.

Carroll goes on to state the following:
   ...the demands of eventually reconciling general relativity with quantum mechanics suggest to many that the metric will ultimately be revealed as a concept derived from a more fundamental collection of degrees of freedom.... 
    So that we are left with the possibility that curvature of the metric on spacetime may not ultimately be the cause of gravity and the "graviton" will not be a quantised perturbation of the metric field.  GR is an effective field theory only.
It is just one of those interesting things that in this effective field theory, the metric field doesn't just describe a fundamental particle (or approximately describe it),  the metric field also directly determines how we measure lengths and times.   Most of the time, such as in the LIGO experiments, it is the distortion of lengths that we measure.  A Gravitational wave may be indicative of a bundle of gravitons travelling through space but in most quantum theories of gravity, gravitons are still being exchanged even where the metric field appears to remain static (upto the limit of our ability to measure it or determine the absolute positions and lengths of separtion between any two objects).

It's late, I'm going to try and put the image in the right place and then sign off.  I don't know if any of the above helped.

Best Wishes. 

3

General Science / Re: What is Energy? Like, seriously, what is it?

« on: 23/09/2021 22:02:36 »

Hi again.

That still doesn't explain why energy exhibits the bizarre properties that it does (e.g. light interacting with matter and black holes the way it does....

   +similar references to energy in earlier posts.

      Light isn't "energy", at best it's one form that energy can take (if indeed you think energy takes forms).   Light can interact with  (stuff)   and transfer momentum to  (stuff)    but that's a property of light, not a property of energy.  Popular science will treat light as if it's the most pure form of energy but it's just because people have to imagine something as energy.  There are phrases in common use like "matter and anti-matter annihilate to leave pure energy" but it's an inaccurate phrase.   They produce something else so that total energy and momentum is conserved,  there is no good reason to assume what they leave behind (photons) is pure energy only that these things (photons) have or contain energy.
      We have never isolated a quantity of "energy" and put it in a jar.  No one has any expectations for what energy would look like, smell like, taste like or how it would behave.   How much volume does 1 Joule of energy occupy?   There are many physical characteristics that we cannot ascribe to energy.  As uncomfortable as it might be, maybe Energy is just an abstract numerical quantity.

I find it incredibly difficult to think of energy as anything but a thing.

     Many people would do the same.  Sadly, nature doesn't really care what seems sensible to you (any of us).

I don't claim to know what energy is.  I don't think it is any tangible thing.

Best Wishes.

4

Physics, Astronomy & Cosmology / Re: Does gravitational time dilation/GTD really cause gravity?

« on: 23/09/2021 13:17:15 »

Hi.
 Well this is one of the more interesting and polite discussion happening here today, I hope you won't mind if I join in.

@Halc and in defence of @TommyJ ,    some sources of information do consider gravitons as the force carrying particle responsible for the force gravity.
   For example, in a school A level syllabus  (age 16-18 in the UK) this is exactly what pupils would be taught.

Wiki  also goes along these lines:
It is hypothesized that gravitational interactions are mediated by an as yet undiscovered elementary particle, dubbed the graviton. The three other known forces of nature are mediated by elementary particles: electromagnetism by the photon, the strong interaction by gluons, and the weak interaction by the W and Z bosons. All three of these forces appear to be accurately described by the Standard Model of particle physics. In the classical limit, a successful theory of gravitons would reduce to general relativity, which itself reduces to Newton's law of gravitation in the weak-field limit.

   However,  gravitons haven't been observed (for example at the LHC) and remain theoretical.  They are also slightly different in theories of quantum gravity.  It is difficult to reconcile gravitons as force carrying particles with General Relativity and geometric curvature.    Both versions of what a Graviton is (Halc's  or  TommyJ's version) are hypothetical and used in the literature.

Best Wishes.

5

Just Chat! / Re: Quality of discussions

« on: 22/09/2021 22:54:02 »

Hi.
It's taken me a while to read what you've written,  Furious Cat.
This is my summary:
   1.  You're here in general to gain input and information.
   2.  You were initially here to get some little questions answered.
   3.  You're here to represent / Support Australia.
   4.  You feel that you can contribute something.

Thanks for your time and for that information.  That's all perfectly sensible.

    There's obviously a lot of other things you said.
I can't really support an attack against the Moderators.  I can understand what they do and why.  They don't always get it right but that's the same for all of us.  Presumably, you also know that they can edit most posts if they felt a need.  I've been on other forums where moderators will edit posts and/or just remove them entirely without much justification.  Sadly, this isn't some kind of legal system where you can get a fair hearing and have any capability to bring something to an independent tribunal.  This is a free to use website and the terms and conditions are set out clearly.
   See  Forum Acceptable Usage Policy  https://www.thenakedscientists.com/forum/index.php?topic=8535.0

10.The moderators are the final arbiter.....
    A moderator may choose, where they feel it appropriate for the good order of the forum, that they should themselves edit or delete a post submitted by a forum user.......
    In all matters, the moderators' judgement is final....
   The moderators are merely volunteers trying their best.....
 

Summary
   There isn't much point trying to offend the moderators.   This never was a fair and level playing field to start with and it never claimed to be one.  It's just a free to use website.
   As forums go, this one is extremely tolerant and liberal (in my opinion).

Best Wishes.

6

Just Chat! / Re: "Why are piple so unkind"?

« on: 20/09/2021 21:50:21 »

Hi.

I can't really really say thanks for that message or put a  "like" on that post,  it would be oddly self-serving.

I'm just fortunate that I don't have to be a moderator or anything.  I don't have to do anything people won't like.   I get seen on the posts where I can help and I leave the posts where I would feel obliged to say something the other person won't like.  It's easy to look kind if you do that.

There's also nothing in particular I want from using this website.  I'm an ordinary person and use the forum to occupy my time rather than .... playing a game on the computer,  or going back to bed  etc.   I could probably use my surplus time in some better way -  pick up litter in the streets,  help at a soup kitchen, cut the grass in my garden  etc.  It's easy to think I might be doing something useful here.

Anyway, could I ask why you are here or what you were hoping to get from your time on the forum today?  I've got a thread here,  with a survey that will take 10 seconds   and/or  you can reply in the usual way:
https://www.thenakedscientists.com/forum/index.php?topic=82722.0

LATE EDITING:  Sorry, it's been a while, looks like I didn't have a quick-reply survey on that thread.

Best Wishes.

7

Just Chat! / Re: "Why are piple so unkind"?

« on: 20/09/2021 12:38:16 »

Hi.

   I assume it's because we notice the unkind ones, it's far more memorable.  We overlook the ten other people who walked past us and didn't say or do anything unkind.

   I took my daughter to a city yesterday, she was starting a new course and discovered she had left her laptop charger at home.  Anyway, cutting a long story short....  I asked a lady for directions to a shop as she stepped out of her own house.  There was some conservation and she went back into her own house, brought out a laptop charger cable and said my daughter could borrow it for a couple of days.  You see, it was late on Sunday night and there weren't going to be any shops open.

Best Wishes.

8

Just Chat! / Re: Not so good YT videos.

« on: 18/09/2021 03:13:19 »

Hi.

Does L continue to accelerate towards where P was?

   Yes, more or less.  This is more complicated than you might have realised.  It's also too late for me to find the references I would have wanted.  I'll try to add them later if you wanted more information or more proof that things can be this weird.

Anyway, here we go with the answer:
   At the instant of annihilation,  yes.

   On the very short term, just after the annihilation of the positronium, something slightly interesting happens -  the acceleration of the lepton should continue to be towards where the positronium would have gone (i.e. as if the positronium had continued along it's trajectory with the same velocity and hadn't annihilated).   This is slightly different from pointing to where the positronium  was.....   it's as if the Lepton thinks not only that the positronium is still there but that it has also continued to move.
   
    After that there should be a smooth and progressive change.  The general idea is that the pair of photons will become a source of gravitation equivalent in magnitude to the original positronium.  As the photons move away, the metric field will change.   It's the photons that will be the new source of gravitation and the gravitational attraction will be towards the photons (wherever they may go).   You've given us a pair of photons, so we have two accelerations and need to do a vector sum to find the net acceleration - but it's not too difficult.
   
- - - - - - - - - - - -

U may care to check out my reply to Halc in How close are we from building a virtual universe?
It may shed some light on your Lagrangian Mechanics - Why is Nature lazy?

   Thanks.  I have read it and will try to keep an eye on further developments.

- - - - - -
I'm tired, bye for now and best wishes to everyone.

9

Physics, Astronomy & Cosmology / Re: Could we fathom the depth of the Earth?

« on: 16/09/2021 23:13:11 »

Hi.

How did the movie explain the nuclear stuff climbing back up on the other side?

  I saw the film.  It wasn't good.  I'm not sure it explained a lot.
   Also, it never actually happened.   There were people talking around a table but nothing actually did seem to happen.

10

Just Chat! / Re: Not so good YT videos.

« on: 16/09/2021 18:20:12 »

Hi everyone.

But we do have instances of small masses evaporating into massless photons, with absolute conservation of energy and momentum, so what happens to the gravitational field of the electron-positron pair?

   We've had similar discussions before, Alancalverd.
I think this is the thread: 
  Problems with PopSci articles in GR. Should we stop using one example?  -  started by  Eternal Student 19/05/21
https://www.thenakedscientists.com/forum/index.php?topic=82317.msg640621#msg640621

   I'll try to keep my reply brief rather than repeating the previous discussion.
   Where matter annihilates to form photons,  those photons have energy and momentum.  As you (Alancalverd) stated they have exactly the same energy and momentum as the original matter.   As far as general relativity is concerned, those photons will be a perfectly good source of gravitation.  Since there is precisely the same energy and momentum at the same places, the metric field   (or the gravitational field)  doesn't change at all.  (Well, it will change in a progressive way as the photons travel and move away but it won't be the "instant" change that was shown in the video and is generally implied whenever people talk about the sun suddenly disappearing).
   Anyway, "the gravitational field" that was caused by a positron and electron doesn't just disappear when the particles annihilate, it's still there but now seemingly caused by the photons rather than the massive particles.
- - - - - - - - - - - -

That's exactly what Prof.Brainy Greene/horn/e said, in his 2011 The Hidden Reality book in a footnote on p34?
But what does it really mean? Even at the surface of the Sun, GTD is practically nothing!

    What does it mean?  I suspect that referring you to the first couple of chapters in a textbook on General Relativity would be better than assuming I can explain it in some better and shorter way here.  (I'm really not that good at explaining stuff).   There's a lecture series by Prof. Leonard Susskind that I watched first before reading Sean Carroll's book.

   I don't know your initial level of experience in this,  all I can say is that it could take a few weeks before it makes sense  (sorry).
   Personally, I don't think it's fair to say that the time component of the metric explains the motion we observe here on earth in what we consider as our gravitational field.  It's the assumption that objects naturally move along geodesics that is pivotal.  I'm probably arguing over abstract notions that make little sense to you anyway.  You need both things to make sense of the movement of objects in the gravitational field around planet earth (and a few weeks to study it all).
    I don't know if it helps but there are dozens of questions I still have about General Relativity.  For example, why should objects tend to move along geodesics?  It relates to another thread in this forum about Lagrangian mechanics and a least action principle but I don't suppose it's worth explaining the connection here.  Anyway, timelike geodesics are paths taken by objects with mass.  These paths maximise the proper time experienced by the object given that it was required to move from an initial event to a final event.  So we could answer your (curious cat) question about why GTD is important to explain motion in the presence of gravitational field in this way:  An object moves along a path so as to maximise the proper time that it experiences.  It will naturally tend to move into a region with a greater time dilation to take advantage of this and maximise the proper time it experiences.  Don't get me wrong, it's not a very satisfying answer and it just deflects the key question from one thing to another.  We can now see why time dilation is important and why an object tends to fall into a gravitational well to experience time dilation but we have another queston to answer:  Why does Nature care about maximising or minimising something?  It might be best to start learning about GR with the attitude of "shut up and calculate" similar to Quantum Mechanics.  Don't ask why things move along geodesics, just accept that they do.  Do the calculations and you will see that the time component of the metric around planet earth is what's important and explains most of the motion that we observe for projectiles launched from earth.

Best Wishes.

11

Question of the Week / Re: QotW - 21.09.13 - Where does the extra energy go when light is stretched?

« on: 16/09/2021 15:31:15 »

If we have a radio tower and it is transmitting a signal let's say 27 MHz and now we move the tower at a very high speed away from us the 27MHz will be transformed into a lower frequency say 20MHz we will still receive the transmission but at a different wavelength. Am I with it now or still off the page?

   Yes, that's correct.

12

Question of the Week / Re: QotW - 21.09.13 - Where does the extra energy go when light is stretched?

« on: 15/09/2021 21:54:07 »

Hi.

Quote from: Kryptid on Today at 00:14:49

    Energy is.

How is energy lost as a result of redshift?

   Obviously I'm not Kryptid.  I'm just assuming you won't mind an answer from anyone.   

   Don't consider light as a wave for a moment, put all your ideas about compressing a wave of electromagnetic radiation on hold for a moment.   Instead let's consider light as something comprised of particles.
    It it is possible to imagine a single photon travelling through space.  Let's not allow it to interact with anything, get absorbed by anything or do anything interesting other than travel through space.
   A photon carries a certain amount of energy  which is given by the formula   Energy = hf    where   h is plancks constant and  f is the frequency of the photon.
   The general idea is that if the photon redshifts as it travels through expanding space then this means it's frequency drops and the amount of energy it is carrying decreases.   Does that make sense or seem reasonable?
    We haven't allowed the photon to interact with anything, it's had no opportunity to pass on or transfer that energy to anything else.  Energy has just been lost as it travelled.

   So, just by considering the travel of a single, isolated photon,  we are in a situation where the redshift of that photon would imply that energy has been lost.  Conservation of energy seems to have been broken.   Does that make sense?   We don't really need to worry about other situations like a wide beam of light as you described earlier.  Yes, a wide beam might scatter more, spread out the wave or "thin it down" as you described earlier.  It could be exactly as you described earlier.   We don't need to worry too much about that.   The important thing is that there is at least ONE situation where the redshift of light from a distant galaxy would imply that energy was lost.  That's all we need to worry Physicist's.  The conservation of energy doesn't usually break in ANY situation.   Does that make sense?

   The redshift of photons as they travel through expanding space implies a situation where energy is not conserved.  The earlier posts in this thread all relate to explaining how this happens; why it happens;  how it can or can't be explained just by the movement of the source relative to receiver  etc. etc.
- - - - - - - - - - -
   

If we look at a galaxy that is one billion light years away we see the light as it was one billion years ago the galaxy is most likely in reality not in the location that we are seeing it in now it may be many degrees in any direction away from what we are seeing now.

  This is mostly true.  I haven't fact checked it, so it might be entirely true.

Is this related to the curviture of space or is it not related at all.

   It's not really related.   I mean all movement and evolution of the universe is related somehow but I don't think this is a useful way of understanding curvature.
   Explaining the curvature of spacetime is a big topic, it might be better in a new thread, although to be honest it might be faster just to look for some existing articles, books and/or videos that explain this.

Best Wishes.

13

Question of the Week / Re: QotW - 21.09.13 - Where does the extra energy go when light is stretched?

« on: 15/09/2021 12:34:57 »

Hi.

If we take a given galaxy let's say a billion light years away and we conclude that it is redshifted and we conclude that it is moving away from us at 10% the speed of light

    Firstly, what do you mean by moving away from us at 10% the speed of light?
    Most people would assume we can measure the distance between us and the distant galaxy and then see how this changes with time.   In school you would have been told that this formula holds:
     Speed =   

    Is that what you mean?    The rate of change of distance with time   =   10% speed of light =   0.1 c

   For flat space, this is a perfectly sensible idea of speed and it is easily converted into a velocity.  The velocity of an object is just a vector with magnitude equal to the speed and direction given by the direction of travel.

    However, in curved space things are more complicated.  We can still calculate something we can call a speed of recession and it is exactly as described above - it is the rate of change of distance with time.   However, that speed does not convert into a velocity in any sensible way.   It is possible for the distant galaxy to move in a direction that just doesn't exist as a direction we can have in our solar system.  The velocity of the distant galaxy is meaningless when regarded as a velocity that something could have here in our solar system.

   Let's take a simple example of curved space.   The usual example is to consider the surface of a ball.   This will be a 2-Dimensional space.  It's useful because we can embed this space in our usual 3-Dimensional space and then we have a way to see or visualise the curvature.

Here's a ball:



Our space is going to be the surface of that ball.  We exist like little ants, forced to move in ("on" but it will be easier to say "in") the surface of the ball.  We can move along the surface but we cannot move out of the surface.  The 2-D space of the surface is the only thing we can experience.  Now consider a point in our space which we will say is at the North pole of the ball.  At that point in space we can move, or have velocities that are shown in the diagram above.  This is the tangent plane to the ball at the North pole.  The only velocities we can have are contained in what we can call the horizontal plane.  We'll take the North pole to be the location of our own solar system in the universe.
   Next consider a point along the equator of our ball.  I've shown that on the diagram and marked the corresponding tangent plane at that point.  At that point  (which we will take to be our distant galaxy), we can only move (or have velocities) that are contained in the vertical plane.  In particular, there is one direction of movement (straight up and down) that we can have at the equator but we cannot have at the North pole.  If we had this vertical velocity at the North pole it would move us (the ants) straight out of the surface of the ball.  It's not allowed, it's not a velocity that exists at the North pole, we are constrained to move in the surface always.
   
    Now, this is where you should start to recognise some of the problems we run into in curved space.  It is possible for a distant galaxy to be moving in direction that makes no sense at all (like straight down) when we are considering space from our location at the North pole.   It can be moving in a "direction" that does not exist in our solar system.  So we are unable to say that the distant galaxy is "moving away" from us.  There is no direction we can point to and say it was moving in that direction.  It is moving in a direction that is "invisible", "inaccessible" or just "nonexistent gibberish" in the local space that we are located in.   

    None the less, we can measure the distance between our solar system and the distant galaxy - we do this by stretching a piece of thread from us to the distant galaxy and keeping it within the surface of the ball all the way.   So we can observe a change in that distance as time progresses - so we can calculate the quantity described above and called the recession speed.  The recession speed makes sense just as the rate of change of distance with time,  however, it is not the magnitude of any velocity that the distant galaxy had.

   Anyway, these are the problems we run into with space that isn't flat Minkowski space.  For an expanding universe, the distant galaxies aren't really moving "away" from us.  At best, they are moving in a direction that doesn't exist or makes no sense in our local solar system.  All we can establish is that the distance between us and the distant galaxies increases with time.  This is something we can call a recession speed but we must be careful not to assume that the entirety of space in the universe is flat and therefore not to treat that recession speed as if it is a velocity through ordinary flat space.

   I hope this helps or makes some sense.  Best Wishes.

14

Question of the Week / Re: QotW - 21.09.13 - Where does the extra energy go when light is stretched?

« on: 15/09/2021 00:00:38 »

Hi again.

@Just thinking,

   It's difficult and possibly repetitive to explain where you might have gone slightly wrong.
First of all, there's nothing wrong with what you've said at all in situations where a Doppler effect applies and it is just that the source and receiver have some velocity relative to each other.  If space was just flat Minkowski space then what you've said would be perfectly fine.
    The main problem for the expansion of space is that there is no way to determine the velocity of the source relative to the receiver.  Even in situations where both source and receiver seem to have 0 velocity through space (they are co-moving) so that you might reasonably expect them to be at rest with respect to each other,  some redshift is still observed.    To paraphrase this, there is no way to know how much of this "compression" that you describe can be explained just as the movement of the source relative to the receiver.   All we know is that where space expands, each individual photon will be redshifted as time evolves whenever it's frequency is determined in the co-moving co-ordinate system.   It could be that we are using the wrong co-ordinate system but there just isn't a better frame we can use.

     This is complicated, so I'll try to phrase everything another way:
We can divide the universe into a large number of small patches of space.  In each little patch, everything behaves just fine, special relativity and/or flat Minkowski space describes the situation just perfectly.

--|----------- |-----------|----------- |--
  | patch 1 |              |              |
  |              | patch 2 |              |
  |              |              | patch 3 |
--|-----------|----------- |----------- |--

   We can't easily extend a frame of reference from one patch over to cover another patch but it doesn't matter too much:  In each patch there is a frame of reference that seems perfectly natural and the most sensible one to use.    For an expanding universe, what we observe is that when a photon moves from one patch to a neighbouring patch, it is redshifted or seems to lose energy.   The original frequency left the first patch, taking an amount of energy E= hf   out of that patch   but the photon entered the other patch with a lower frequency  v < f   and a corresponding amount of energy E = hv.   So not all of the energy that left the first patch made it into the second patch and we don't really know where the difference in energy went, it didn't seem to go anywhere.   

    It could very well be that we just weren't using the right reference frame in the new patch but there is nothing that we can do about this.   This is where General relativity significantly differs from Special relativity.  We can't pick up the reference frame from patch 1 and use it in patch 2.   For example, we might try and use a different reference frame in patch 2 that is moving toward patch 1.  We can give the photon coming in from patch 1 exactly enough blueshift in this new frame to counter the redshift it would otherwise have had when it moves from one patch to another.  That's great -  BUT  if you glance at the diagram above you'll see that we have made the problem much worse for a photon coming in from the East side (from patch 3 to patch 2).  A photon moving in that direction would now suffer twice the redshift it needed to  (one shift because it changed patches + another shift because our frame for patch 2 is now moving away from the photon).   There is no easy way to define an inertial reference frame for patch 2 where a redshift doesn't occur for a photon coming in from at least some direction.

Best Wishes.

15

Chemistry / Re: Where does firelight come from? And other burning questions...

« on: 12/09/2021 20:52:55 »

Hi again.

Are you (Aeris) happy enough with the answers.  I can see there are a few outstanding questions but I believe some of them can be answered using what's already been said.

Let's take an example:

Q3. Why does complete combustion yield a blue flame as opposed to the standard orange-yellow flame? I know it has something to do with the perfect combination and amount of fuel, oxygen and heat, but how do all of these things come together to form a blue-colored flame?

    I think it very much depends on what you are burning.  For example, if you burnt something with a lot of copper in it then you would expect to get some of the characteristic blue/green flashes of copper in the flame.  It doesn't matter how well oxygenated and how complete the combustion might be, there will be some greenish light.
    For the more typical fuels that we burn (e.g. Hydrocarbons),  it's already been stated that yellow/orange flames are characteristic of carbon and short carbon chains existing in the flame.   If you can keep the fire well oxygenated, for example by mixing oxygen in with the gaseous fuel BEFORE combustion takes place then you can greatly reduce the amount of unburnt Carbon and short carbon chains persisting in the flame.   You don't get the more conventional effects of some incomplete combustion happening low down in the flame and some unburnt carbon persisting into the upper parts of the flame (where they will either continue combustion or else escape as unburnt carbon).  Instead any molecules that start combustion tend to undergo complete combustion almost immediately.   
    A school bunsen burner achieves this effect by opening an air hole on the shaft of the bunsen burner.  Air is then drawn in and mixed with the fuel before the actual combustion reaction starts (which is only at the top of the shaft).

Anyway, if there are more questions you want answered, flag them up again   (i.e. just write something here like "I still need an explanation for Q.10").

Best Wishes.

16

Chemistry / Re: Where does firelight come from? And other burning questions...

« on: 10/09/2021 17:46:13 »

Hi.

if my post really does need some improving here and there, by all means, don't be afraid to tell me so

    It looks good to me.  Thanks for spending some time here.  You're picking up the general rules for using the forum and the features of this interface really fast  (for example, you can quote sections from other people's posts and insert smiley faces).  The grammar and spelling is also good, so you're spending time.  Your questions are quite challenging; you're obviously an intelligent person; you seem to be interested in science and learning  and you're polite.   I don't know what more anyone would be looking for in a forum member.

   The only thing I haven't done is check too many of the video links you provided.  Obviously people get paid for having more views of their YT videos and this becomes a grey area with respect to advertising.  It's perfectly fine and often really helpful to include some YT videos if you are genuinely talking about the content and keeping in the spirit of the forum  (which I expect you were).  It's only a grey-area if you were deliberately picking videos from yourself and your friends.

...since this website seems to be full of super smart people that know their stuff, I was wondering if you guys and girls could answer some red-hot questions I have about fire, flames and light.

     I do housework as my day job.  I seek discussion here because otherwise I'd be doing the laundry.  Don't overvalue my replies or opinions.  The moderators (which will be identified just under their name) are described as "experts in one or more fields of study" according to the information given on this website.  Their replies are usually quite solid and reliable.  You'll make your own opinions of other members as you go.  In this section,  Chemistry,  I would be expecting a member called "Bored_Chemist" to be contributing some high quality replies.

I had a fishy query not entirely related to the subject of the OP.
But, can a single Atom burn?
Like can it catch Fire?
& Then what residue would be left behind?

     Firstly, single atoms are not very stable objects.  You just don't tend to find them all alone and un-bonded to something in the real world.   The noble gases are the obvious example of something that does seem to exist as individual atoms.   These don't react with Oxygen (they don't burn), they are quite inert (which is why they float around as individual atoms in the first place).

     However, if you did have a single atom of say Carbon, then it can react with Oxygen in the atmosphere.  This is, by definition, burning or "combustion".   It may not not "look" like it had caught fire because fire or flames are a multi-particle phenomena.  One particle of Carbon reacting with one molecule of Oxygen would be unimpressive and we are assuming there are no other particles to get involved with producing a flame.
  What residue would be left behind?   Assuming complete combustion of 1 atom of Carbon with 1 molecule of Oxygen, we expect a molecule of  Carbon Dioxide to be formed.  This will tend to be a gas in ordinary conditions and would float away, no obvious residue left behind.

Best Wishes.

17

Physics, Astronomy & Cosmology / Re: How does Time Dilation happen on on the Atomic Scale?

« on: 10/09/2021 16:16:14 »

Hi again,  I hope you are well.

Keyword - seal level pressure.

  Did you really mean "seal"?   That's an animal.  If you meant atmospheric pressure which is highest at sea level, then that's OK.

Similarly, what factors in while travelling through SpaceTime?

Is it the movement, or acceleration.

    At the simplest level, we can use Special Relativity.   It is the velocity of one object relative to another that is important.  The objects do not need to experience an acceleration.
    The only reason why an acceleration might be important (as it is in the "twins paradox") is that we can't easily compare two clocks unless we bring them back to the same place eventually.  We need some acceleration to alter the straight line motion of an object and bring it back to the other object.

Say, 2 clocks at rest in a common reference frame.
They start moving apart slowly.
They become unsynchronized.
But Why?

     Because of stuff in special relativity.  I could say it again if you wanted but there are plenty of other articles and videos about this.  I suppose we could say that "time dilation must happen because otherwise there isn't a way to explain why light always seems to travel at the speed c in a vaccum".
     This is essentially saying that it must happen and avoiding explaining WHY it happens.  The deeper explanation of why it happens is beyond me and the subject of many articles across many fields like Physics and Philosophy that would fill this entire forum.

The other comments you make and questions you ask are similarly complex:
   What connection does inertial movement have with Time?
   What relation does mass have with Time?

- - - - - - - - - -
   It seems that Halc has replied before I finished this post....
  A lot of his comments relate to a  "Triplets paradox"   which isn't a real thing  but just a sensible way of extending the  "twins paradox" that has become a conventional part of Special Relativity.
    Consider triplets this time and not just twins.    We keep one sibling on planet earth as usual.  Meanwhile we send the other two siblings off into space for a round journey.  We send these two in opposite directions and keep everything (like the speed of travel and distance travelled) perfectly symmetric but just mirror-images of the journey as far as the sibling staying on earth would be concerned.
     We see that we have done the twins paradox situation twice.   The sibling on earth disagrees with the elapsed time that the space travellers report.  However, the two space travelers will agree on their elapsed times.  The two space travellers were moved apart and brought back together again but it was done in such a way that their total elapsed times agree.
     Time dilation is complicated and it is possible to expose two clocks  (the space traveling siblings) to different accelerations (opposite in our case) but if we can find an inertial reference frame in which their speeds (a scalar quantity not a vector) were always the same then the clocks remain in sync in that frame throughout the entire motion.   In our example, we can choose the frame of reference for the sibling who stayed on planet earth.

Best Wishes.

18

General Science / Re: I can see infrared and hear ultrasound. Am I an abnormal human?

« on: 10/09/2021 14:35:01 »

Hi.

   Seeing infrared is unusual.  We might expect a little variation among human beings for most things we can sense that involve some mechanical process of detection.  For example, hearing sounds into the ultrasonic range.
   It's a little bit stranger for eye sight because a lot of it boils down the ability of a particular molecule to absorb a photon.  This is not a mechanical process.  If you had some genetic variation that made your photosensitive molecules different to most other people, this would probably make you blind to certain colours.  It's likely that even a small change in those pigments would stop them from working at all, rather than making them favour slightly longer wavelenegths.

    I found this article on the internet:  https://www.sciencedaily.com/releases/2014/12/141201161116.htm
I don't know how reliable it is.   Their findings were apparently published in the "Proceedings of the National Academy of Sciences (PNAS)".
   It suggests that, in some cases, the standard pigments in the retian can absorb two low frequency photons in short succession and this can trigger the usual chemical changes in the pigment and cause a signal to be sent along the optic nerve.  This usually requires the infrared source to be "pulsed" (rapidly turned on and off) which might be exactly what your IR remote control is doing.  Anyway, they used a laser which produced IR radiation and this is what they said:
    .... packing a lot of photons in a short pulse of the rapidly pulsing laser light makes it possible for two photons to be absorbed at one time by a single photopigment, and the combined energy of the two light particles is enough to activate the pigment and allow the eye to see what normally is invisible.

   It could be that your eyes (the lens, the cornea, the vitreous humor etc.) don't absorb or filter out as much IR radiation as most other people.  So other people don't generally experience two IR photons hitting the photopigments in the retina in rapid succession  -  but you do.

Best Wishes.

19

New Theories / Re: Does Free-Will Exist ? (Lightweight topic......... lol)

« on: 09/09/2021 22:06:42 »

Hi everyone.

  For whatever it's worth, it seems Halc is covering the topic adequately.
Many people would suggest that "Free Will" does exist   - but it may not be what you thought it was.

I guess my definition of free will is my making choices based on my own way of making them. Completely independent of any subconscious , back-of-house programming that I do not have control of.

    You already have some direct experience of this.   You cannot keep your eyes open when an object (like someones finger) is coming toward your eyes.  There's an autonomic response that will close your eyelids.
    So you can "choose" to keep your eyes open but it doesn't matter, you can't make it happen.  There is some "back-of-house programming" that will take over.
    However, I shouldn't worry about it.   You can "choose" that tomorrow will be a nice sunny day but you can't make that happen either.  We don't assume that the weather was anything we should have had some control over.  Our inability to choose the weather does not cause us to think we don't have free will.    So,  the autonomic closing of your eyelids and 99% of everything your body does can easily be put in the same category.
    So, we can see that "Free Will" already means less than we might have hoped for.  There isn't much that we actually have conscious control over.

Best Wishes.

Late editing:   Hi evan_au,     if you had got your post up earlier I would have included you in my reply.  Anyway, it seems sensible.

20

Just Chat! / Re: Why is pi irrational?

« on: 01/09/2021 17:14:02 »

Hi.

   At school level you just wouldn't prove that π is irrational.   The standard proofs are either complicated and require too much prior knowledge or else just exceedingly laborious.  You run the significant risk of scaring the children and/or boring them to death.  This is the opposite of what you normally want to be doing as a maths teacher, you're supposed to let them see how much fun and how interesting mathematics can be.  It is much quicker to show them that √2  is irrational and this establishes that at least some irrational numbers exist.

   If you must have a go at proving that π is irrational, see this YouTube video:     "Pi is IRRATIONAL: animation of a gorgeous proof"  by Mathologer.   

   That video takes almost half-an-hour and the presenter was using plenty of pre-prepared animations to do this.  There are some bits that are rushed and you would want to stop the video and grab your own pencil and paper.   If you had a sixth form class (age 16+) and a 1 hour lesson, then you might be able to show the video and fill out the bits that were overly forced to get close enough to a complete formal proof.

Best Wishes.