geordief

Is the idea that this expansion was initiated at some point and that it is continuing wherever we look "under its own steam" or inertia as it were ? (aside from Dark Energy which seems like some godawful joker in the pack) But to come back to my "expanding into itself" notion can we posit a moment in the evolution of the universe where there was no distance ** between objects so that the space that there came to be subsequently between the constituent parts of this earlier unified object came out of that object (so that the later distinct objects and the space between them could be seen as the two fundamental elements of the earlier unified object) If there was a time when all the matter in the universe was gathered in one object can we see this object as having evolved into (1) the later distinct objects and (2) the space between them? Or is "space" just another word for "distance"......? ** does that notion imply an impossibly perfect symmetry?

Fueled by word choices such as the "Big Bang" it was always a temptation to think of an initial event where the Early Universe started from a well defined point and grew into an existing Space. But this, we are told is not what happened and it is said that everywhere is the centre of the Universe . Trying to make sense of this (I suspect it may not be too hard or counterintuitive,moreso that I may be "making a meal of it") can I view the situation as the Universe "expanding into itself"? And,if so is the "space" it is expanding into created by itself and equivalent to the distances between its constituent parts?

The man from WHO (some Irish sounding guy ; is he the head?,the chair?)was just on the TV saying vaccination passports for international travel were a bad idea as they reinforced the inequality between countries via a vis access to vaccines in the first place.

No harm in that but it is clearly in its (and everyone's) interest that enough vaccines are available in all parts of the world ,and as quickly as possible. Pay them if necessary.

Is motion just the natural order of things and so we are really asking what changes motion? In any system is there a process of seeking a balance and this process is unattainable so motion continues? And why is there a favoured direction of motion (along geodesics)?

Reaching the sufficient number of vaccinated may be a difficult ask so it is important to not alienate those who are hesitant to take the vaccine for any real or imagined reason at all. These people have to be accommodated as much as possible (I appreciate some lives may be lost as a result but that is hopefully short term)

Best of luck and thanks for all your help over the past 10 years or so.

Is the tiny distance between the head and the feet a misleading example? Would whatever is seen,(or not seen) be essentialy the same as if the distance was the same as that between any object and an observer say 1,2 or 1000 light seconds away? So the object crosses the EH in its own timeframe and the observer sees it up until it crosses the EH in the observer's timeframe. And the timeframes differ.

Should /could I have placed the "earthbound" clock at the centre of the Earth?

Actually ,no I didn't have that particular scenario in mind.I was just very generally thinking of two clocks that ,either one or both accelerated. And that ,if they did accelerate (under their own steam and provided possibly that they did not both accelerate "equally" ) then they would tick at different rates. Sorry ,I missed your post.I will have a look at it a bit later. @studiot I don't see the problem with my scenario. Can you not have a clock on the surface of the Earth and another at rest wrt it at say 1 light second from it (or from the centre of the Earth)? This second clock will , from rest move towards the first clock and eventually they will come together. I realize now that these two clocks will tick at different rates ,but when I asked the question I imagined the opposite might be the case (and the freefall might have kept them aligned) (The inertial coordinate system I was using was that of the "Earth bound" clock)

Your speed is only zero wrt the centre of gravity of the field. You are in motion wrt all other points. Anything to that?

So does that not suggest that the two causes of time dilation have a connected cause? Is there a sense in which they are entirely distinct?

You ca't have acceleration without implied motion can you?

Is there a connection between those two kinds of time dilation? Is it simply that the one cause is the derivative of the other ?

(hope I am not just repeating myself) If the one clock is in freefall(my earlier scenario). ,it does not experience acceleration yet still ticks at a different rate... Is that because the two clocks are still in relative motion? And so the only time they tick at the same rate is when they are both at rest and also experience no (different?) acceleration?

Is there anything special in the (temporal) relationship between a massive body and an object freefalling towards its centre of mass without any lateral motion? I had it in mind that their clocks might tick at the same rate but it seems that they don't. What about if their distance is artificially maintained through acceleration? Do their clocks tick at the same rate for that duration?

Well ,I was wondering whether it was possible to set a ground clock and a distant clock to the same time at a particular instant and thereafter the distant clock approaches the ground clock directly** in freefall. Will the two clocks still show the same time when they meet? ** ie no lateral movement but all movement is along the shortest path.

Suppose we have two reference frames that are not at rest wrt each other (even accelerating). Is there any way at all that a observers in their respective frames can agree upon a mutual time? Is there any way at all for the to synchronize clocks ,if only for the one instant?

Will there be enough generations remaining in our global (human) civilization to put these scenarios to the test? I imagine (without knowledge or research) that your descendants would acquire the characteristics appropriate to their place of living but how many generations it would take,I could only guess at. 10 or 20 ?

Thanks. I did try replacing "if"with "is"....I need to try harder

I don't follow this part .A typo or two? An autocomplete malfunction ?🤔

Is this at all related to the relationship between two objects one of which goes behind the event horizon of a BH and the other that does not? (I thought I saw that scenario mentioned quite recently somewhere on the forums)

How would you organize the collection of spacetime intervals intervals so as to potentially turn them back into a reality? Would you have a local origin(the start of the first interval) corresponding to the apex of a light cone?

Is there a silver lining to be drawn from the current situation? Are the opponents to concerted action based on scientific understanding who have shown their hands on this occasion broadly the same group we can expect to be digging in their heels when it comes to any action at all when the time comes (of course it has come but seems to be being deliberately ignored-eg the windmills in Texas ploy) Are we getting any closer to a very widespread acceptance that we are all in this together in a very shallow pool or has the populace shown themselves to be ready for more snake oil merchants who will offer them short term satisfactions and attempt to turn us one against another for their own gain? On a practical level are their any parallels between the measures required to fight this pandemic and the mobilization required to address climate change?

Is that the same thing as differentiability?