geordief

Is inflation/expansion theorized to have started before there was relative motion between objects? (before there were objects?) Or did the two phenomena start at the same time? Is there any connection at all between the two phenomena or is the similarity** just on the surface? **I mean to an observer (in the layman sense) they seem similar.

Do we have evidence that this expansion /inflation was/is entirely the same wherever we look in the Universe? On the large scale, I imagine as locally (on small scales) we don't see it ,do we? I am just wondering if there is a connection between relative motion and inflation or whether these are two entirely unrelated phenomena.(they do seem awfully similar on the face of it) Is inflation kind of like a background where relative motion does its own thing ? Did inflation come early on and relative motion later on ? Did the former "bleed into " the latter in any sense?

Fanaticism and Doubt seems a bit Pythonesque I suppose heresy is as old as faith- and comes in useful at times.

You are well located to say.I assumed Poseidon was able to use lightning over water ,but have no examples in Greek literature where this was claimed. But I thought he raised storms at sea and they would have been tame affairs without thunder and lightning. Did he have to get permission for these embellishments ? Did Zeus have an ongoing armaments trade with Poseidon and his minions?

That's just a Vespa.I was more of a Lambretta man.

Does iNow have some kind of a Poseidon complex?

I wouldn't mind an electric scooter.

Holy mother of Buddha,don't listen to Maya https://www.ramakrishnavivekananda.info/vivekananda/volume_2/jnana-yoga/maya_and_illusion.htm "Maya, Maya, all this world is but a play Be thou the joyful player" https://www.youtube.com/watch?v=SCRVkyt74Ig&list=RDSCRVkyt74Ig&start_radio=1

That is a base accusation.

That is a relief.

Thanks for that scenario which was new to me in its specificity and which I have now read carefully. Most illuminating and very helpful. I need to ask you though ,why you needed to write"Professor Beiser has written this little piece especially for people like you" ? (my bold) What is my kind of people as per your judgement?

I most certainly am . It is just that pressure of time ,allied with natural and increasing slowness/dullness of thought ,allied with similarly attributed obduracy means that I have to give myself long periods of time to respond to some posts that require especially long attention. You often seem to be able to drag up links that go to what I have in mind in particular threads and the last one (about Newton's law of reaction iirc is still, some two weeks later sitting on my desktop waiting for me to get round to it (there are 2 or 3 pages of Einstein's exposition to read...) So ,thanks for your patient answers and directions over the years ,, but there is the old adage about horse to water (it can just take me a very long time to make my way to the trough )

Suppose we accelerated into the Sun and visually recorded our trip,would we notice any difference from a similar recording when we only moved towards the Sun at a constant velocity ? (I think in the latter case we would see the Sun slowed down ** but cannot say how we would see it in the former case ) ** compared to at zero velocity I would be a poor authority on this question but,I will try to give you an answer if you promise to take it with a pinch of salt... Newton's laws apparently work only as an (extremely good) approximation at low relative speeds and low accelerations or gravity fields. I should probably not say any more than that since the other people on this thread are far better equipped to give you helpful answers.

I learned Galilean Relativity at school and it was a really satisfying discovery.one that I have never questioned and which seemed far reaching in its consequences in all sorts of contexts. So, yes extremely familiar (in my own mind). What happens if an observer accelerates towards the source of the light versus the Galilean scenario of one ship accelerating in the direction of the second (where the relative speeds of the 2 ships increases) ? Does the measured speed of light increase as we are now no longer talking of inertial frames?

I am trying ,in my own mind to get a handle on how the invariance of em waves works. That example was the closest I could find of a scenario that seems to have a relationship with one of the properties I associate with that invariance.... the speed of light is the same no matter what the nature of the relative motion between the observer and the source of the em. I appreciate my understanding of invariance is (very?) incomplete ,but it would be helpful to me to know whether this parallel between my scenario and the invariance of em waves holds in this one aspect. btw this from Eise in the second post of the thread I found very interesting "A not quite historical reconstruction of Einstein's thought is that Galileo's principle of relativity also applies to electromagnetic phenomena: there is no experiment from which you can derive if you are in constant motion or not. Therefore the speed of light, as an EM phenomenon, can neither be used. You cannot measure the speed of light, and from there derive what your movement is. This means, everybody measures the same speed of light, independent of their (constant) velocity" and I have been trying to understand it

OK ,so I will drop the descriptor "invariant" but does my scenario hold any interest? I have an observer in an idealized medium* ,whose constituent parts are all "at rest" wrt him/her (approximately as everything always exhibits relative motion to some degree) Am I right to say the the wave emanating from any disturbance in this medium will reach the observer at the same speed no matter the direction of the source of the disturbance? If that is the case ,then it may give me something to think about .... if not , ditto. * I had water in mind but it could be anything.

Are there any other instances of invariance in physics? For example ,if we have an observer at rest wrt any medium and an object at a distance from this observer is in motion wrt the medium ,is the speed of the wave as perceived by the observer and created by the movement of the object the same ,whichever direction this movement is? In this defined circumstance would the speed of the wave be described as "invariant"? The source of the wave could be approaching or receding from the observer and yet the speed of the wave reaching the observer would be the same..... No?

Thanks.I will have to have a look at that later when I get home (on a bigger screen)

Is it better to think of em radiation as (more fundamentally) an expanding sphere than as following any particular trajectory?

Thanks ,that was helpful for me to see how c was related to the permittivity and permeability in Maxwell's equations ,but that only goes so far it seems to me. Constancy does not necessarily show invariance and I think Special Relativity introduced this concept whereas Maxwell did not. I think I understand now that Einstein saw that Maxwell's equations had an internal contradiction whereby the two observers (one moving along with the moving charge and the other at rest with a stationary charge ) saw the same interaction differently. I am still trying to understand how the invariance of c sorted this out and am trying to go through the transcript from Feynman's lecture on the subject as I think he is considered to be a clear educator. http://www.feynmanlectures.caltech.edu/II_13.html#Ch13-S6

Thanks everyone. I think I may be more or less up to speed now.

Are the electric field and the magnetic field simply constituent parts of the electromagnetic field? Can the electric field or the magnetic field exist in isolation ? When stationary?

Thanks, I appreciate your patience. (I take your point about those forces acting in a direction perpendicular to the direction of travel of the wave) So what do those forces do? They just serve to maintain the mutual oscillation? The direction of travel is in all directions (an expanding sphere)?

But do these newly created fields "push off" each other in the direction the wave is traveling? There seems to be an electric component and a magnetic component to this moving electromagnetic field. Do they interact with each other in the way I have suggested? ( "pushing off" one another in turn)

I had been thinking about those fields earlier.Does a magnetic wave affect the magnetic field locally and so change the way the local magnetic field affects the electric field? Do the magnetic waves and the electric waves travel through the electric and magnetic fields by pushing off each other in a similar way to a rocket pushing a spacecraft through a vacuum? Am I any way near understanding the process?