michel123456

No I don't. Very kind of you. I was out. So, following your definition of change, there is no change between 2 lines of a derivation? That's astonishing. If I put A=B 2A=2B 2A^2 = 2B^2 and so on there is no change?

Bolded mine. That was not what I had in mind when asking the question. Simultaneity is a description that involves time: it is "zero time". What I asked was more about no time at all, maybe it's a bit difficult to grasp. The example of the mathematical equations on a sheet of paper is the only one I can think of. A derivation is a sequence of equations that are all equals, but different. When you make a derivation, you make some changes, is there time in it?

I don't know. Describing time as duration seems silly. Tautology. Anyway change in duration is some kind of change. If change can only happen in time, then change in time must happen in a sort of "other time"(or maybe the same time). Maybe what we call "time" is emergent. When time changes, another "time" emerges. Putting things a step further, maybe change in time can change, and a time^3 will emerge. Ad infinitum. In a similar way, change in speed is called acceleration, change in acceleration is called jerk, and so on. There is no end to this game.

Very interesting question. See one of my preferred: The multiplication of bananas by umbrellas.

That's my question. If time can change , does it change into "meta-time" as you said?

I'd like to support Greg's point. After all, the constancy of Speed Of Light authorizes to express distances in terms of time interval, and reversally time intervals to be expressed in terms of distance. IMHO if you scratch the surface, there should be no fundamental difference between a distance and a time interval. IMVHO of course.

Bolded mine. I agree. Question: When time itself changes, does time change in time?

No comment.

bolded mine wrong excuse(*) (**). pmb just reached the bottom of the abyss of my unconsideration. Don't worry you are not alone there. (*)quoting and (**) bolded mine No. Bolded part does not look to me as an error of translation from paper to text. And no one goes from Eq(3) to (4) when there is an error in Eq(3).

Time has been presented by some as a measure of change. So the question goes like this: can change happen without time? That is not a question about simultaneity (can a change happen in zero time), that's another question. The question is: if you take an event A and say it changes into an event B, do we need time for the change to happen? For example, in mathematics, one can take an equation and make it evolve in a full page of equations following a sequence that can go forward and backward. Isn't it an example of change without time?

@pmb Bolded mine. "The prope mass m0 of a particle is independant of speed." except for m0= zero. ------------- edit from post #3 you wrote then Are you sure? Isn't it g=E/mc2 ? ------------------------ @Juanrga bolded mine. You are perfectly correct, I mixed things. But in order to do so there must be 2 different things to mix. isn't it?

Done.

I have a problem with that. You all must know I like diagrams: have you ever put this statement into diagram? You get a mass curve increasing with velocity, reaching the infinite a C For zero mass, the object should be at zero mass (tautology): that's the origin, the point A. But no, science tells us that for no mass, the "thing" (the photon) is closer to point B, actually infinitely far up out of the diagram, upon the C line, up, up,up to the moon. But not even, the photon is not infinitely up out of the diagram, the photon is down the C line, at the intersection with the horizontal zero-mass line, at point C. And certainly not at the zero-zero origin point. Which makes no sense to me.

Could you explain this?

bolded mine. 1. We remain in the present, right, but the universe, that's another story. Everything we observe around us lies in the past, not in the present. Today we observe something as it was some time ago. The farther we look, the more in the past. What we observe is a slice of the history of the universe. 2. "where does the passed time elopes"? There has been a mountain of discussions about this on this Forum. Some people here believe that when a millisecond elapses, we continue to live somehow in the past, frozen in time, in a place where eventually we could go back (or not) and find ourselves living in the past. Personnaly, (my opinion) I think it is a wrong conception. IMHO we are nowhere else than here, in the present, and we continue to be here in the present because we "move" through time, i.e. we change continuously coordinates in time. Yesterday you were here, today you are here: you changed coordinates in time. Under that scope, there is no other "you" in the past, the past instant did not go anywhere: you "moved". 3. maybe I am wrong. Anyway your question is not foolish. It has been beaten to death. (I survived)

That is not necessary. You just have to keep falling. Acceleration will be produced by some star or planet somewhere. Acceleration will not be produced by any engine and the spaceship will not have to carry any fuel or anything. In order to get the appropriate direction, the aliens only need to focus on the correct star*. (Its fantasy, isn't it?) And relativistic calculation gives the acceleration as observed by someone far away observing the spaceship, or by the spaceship observing the fellow far away. In this fantasy, one could argue that the actual acceleration has nothing to do with what is observed. edit * deceleration is an issue. I guess the fantasy writer could imagine the alien spaceship focusing on another star (how he would do that is not so necessary to explain) or simply decelerating slowly by orbiting the goal planet.

Hm. at the question "how fast is space-itself expanding"? the answer is: 2.3×10−18 inverse seconds. Ref: The Hubble constant has units of inverse time, i.e. ~ 2.3×10−18 s−1

The only thing you have to do is to accelerate constantly. With an acceleration of 1m/s2, it will take you about 9,5 years to reach SOL (If I calculated correctly). At g (9,8 m/s2) it will take about one year.

So there is no limit to how fast space-itself can expand? Can space expand at infinite rate? And after some more thinking: The word "fast" refers to speed. Speed refers to an amount of space divided by an amount of time. Since space-itself is expanding, can we talk about the speed of expansion? Is this an expansion of 1 meter/sec? Or 500000 km/sec? Can one ask "how fast" does space-itself (the metric) expand?

I learned something today, thanks. But Where else in physics or geometry do we encounter Pi squared?

This is an excellant explanation about what the cautions are regarding the nature of spacetime. I recall countless times people speaking about the speed at which a photon travels through spacetime. You can just as well talk about the speed at which light moves through spacetime as you can talk about rotating a clock into a rod. [/font] So that's the answer to the question I asked a millenium ago: Q. Is time rotatable? A. No. (if i understand clearly your quote) But then: how is it possible that time & space are interchangeable, that space for an observer changes in time for another?

I am confused (bolded mine)Aren't there 2 different trees?

Ioannis has a lack of self confidence, too bad. I hope he'll change his mind and stay here. M.

Why? you cannot disappear at the first denial. if you believe in what you have done, you must fight for it. keep in mind that you are one of the few coming here with mathematics. that makes you one in a hundred (at least), not to say one in a million.