geordief

If only the same could be said of ticks(on the bell end).

Is the "medium" of free space the radiation itself? Those coefficients apply to em radiation: Are there forms of radiation that apply to other fields (as per the fields in QFT)? Eg does the strong force radiate?

Can I just pick you up on that point? I didn't think that Russia (you mean the regime ruling Russia now?) claimed to be Communists. Not that I care very much what they claim to be ,as (a) actions speak louder and (b) lying is what they are best at. Just surprised you might think that. Regarding "fascism" it seems to me that what we have in Russia and possibly emerging in USA may actually be worse than the fascism as practiced in the 20th century. (Not quite sure if it was just Italy that calledcutself fascist or whether Spain shared the same,or similar ideology)

Is there such a thing as "empty space"? If "it" is permeable or permittive then it has a property/properties . Can anything with properties be considered "empty"? And if it is permeable/permittive then does that mean it it "permeated"? -(with radiation?)

Is that a bit of "back engineering" Was it Minkowski who arranged the axes so that they all had the same units of spatial distance? Was he just trying to convert time to spatial distance or did be have in mind (as I always thought was implied) that ct was the distance traveled by light in the units of time chosen by the timepiece? If it was him,did he explain his reasoning at the time?(not that we would need to respect his intentions ,necessarily if the model speaks for itself-I have read that Einstein didn't approve at first) Would the model work as well if c was replaced with an arbitrary speed such as ,for no particular reason the speed of the earth around the Sun ?

Might it be that the quantative difference between the overall spacetime interval and the integral of the causative chain of events is the aging and spatial displacements of the sword? If the sword was a smaller system (and followed a geodesic?) would the difference be less? Also is entropy another description of aging? edit ,am I just repeating what @md65536 posted a little above

Are they related?Can they be the same under any particular conditions? If the worldline of an object is integrated is the result given in the same units as the spacetime interval?(which just considers beginning and end points of the worldline,if I have that right) Edit :just saw @KJW 's response.Probably too late to answer him today...

Imagine a pair of fictional events the first being the murder of Caesar by one of his enemies using a sword and the second fictional event the murder of JFK by someone using the same sword some 2000 years later. The spacetime interval between the two events is calculated by choosing the earth as a reference frame ,measuring the distance between Rome and Dallas ,choosing the units of time and applying the s^2=(ct)^2-r^2 formula. Suppose instead we were to follow the sword across the centuries and make a note of the time and places in which it was recorded as having been prior to it being used again in the fictional killing of JFK. Could we calculate spacetime intervals at every stop on the way,add them all up and end up with a figure that was comparable to the first spacetime interval when we just used the two events? What if the sword had disappeared down a hole in the earth and reappeared in N. Zealand for a time (or had been taken to the moon and back) ? Would that have increased the"cumulative" spacetime interval even though the beginning and the end of its journey were still the same? Sorry if that sounds a bit weird or overly tortuous

Before I saw the young girl ,I assumed he was sitting on the jacks.

If there are different possible definitions of explosions ,might there likewise be different definitions of expansion? Is @KJW basing his definition of an explosion on how things look to a test particle? (as usual I have vanishingly little understanding of this subject and so the question may not be pertinent)

As an avid non reader of the Bible ,but having read that parts of the OT advocates some odious actions can I ask if perhaps there are indeed some passages where rape is advocated, or described in an approving way? Like the good lord I too am fishing ,but for evidence

think so.

Well OK ,but can I repeat the question with just that one frame and the fixed distance between the location of the taker of the measurements in the same frame? (I would have said "observer" but I suspect that might have different meanings ...) If you just have the one frame is there any way to find the concept of spacetime useful as opposed to the pre relativistic separation of it into space and time?

Suppose we have two frames of reference that only differ in that they are separated by a fixed distance And suppose each frame makes measurements of an object that is moving relatively to both at any speed between 0 and c. Is the concept of spacetime necessary for each frame to make that measurement and so that they agree in every case? I am asking this because it has been said (was it by Minkowski?) that our previous till then understanding of space and time must be replaced with a new amalgam of the two (spacetime) and I am wondering if this is because all frames of reference are relatively in motion in practice or whether the reason is deeper than that.

Is the region between,say two BHs a region of negative curvature?(the two beams could diverge if the one moved towards the first CoG and the other beam towards the other) I think I heard(from Markus ,perhaps if I remember rightly) that there are no physical regions of negative curvature and ,so it would just be a mathematical concept.