michel123456

from http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html © 1992—2009 by Scott Chase, Michael Weiss, Philip Gibbs, Chris Hillman, and Nathan Urban I know, it says "in inertial frames". O.K. for the quote above. So are you saying that a bug that walks for 1 sec upon a stretched rubber sheet will physically travel the same distance than a parallel bug walking on the ground ?

Well Spy, my thoughts are that a "local penny" in Iggy's analogy represents an object, at most a cluster of galaxies which is a "gravitationally bound" system and I understand that an observer inhabitant of the "local penny" is inside a gravitational field and thus should not observe C as a constant at all, following Iggy's explanation. My thoughts are that in Iggy's explanation, from an expanding metric POV, there is no possibility to observe anything faster than c, only slowest. That is because the system of reference expands while the distance traveled by light in 1 sec diminishes relatively to the expanding metric. My thoughts are that in Iggy's explanation there is no way to observe anything receding faster than c (see below). My thoughts were that from a "local penny" point of vue, in order to observe something receding faster than c, the receding object must be "carried" by space and its displacement mus be proportional to the grid. And if this is correct, then I'd like to understand how space can "carry" a material object like a galaxy and cannot "carry" a photon. But I wanted to say that step by step because I'd like to understand where exactly I am wrong. -------------- (edit) I don't want simply to "learn" , I want to understand. That is still not an answer to my question.

You didn't answer this question.

Define moving.

Sorry I don't get it. If "the photon always moves as if to cross a local penny in one second", then it is constant. But you just said it is not.

Wonderful. And if the metric of space is expanding, it means that we are currently in the large system C=M/S observing the small system c=m/s. (and a lot of other smaller systems as much as we look far away) Because c=m/s lies in the past. I hope that is correct too.

I can accept that i am wrong but I must understand my mistake first. Is this wrong?

(bolded mine) Isn't it exactly what we are observing? C is constant for us (all photons reach us at C) but we observe galaxies receding at speeds multiple of c.

??? that is forbidden by Relativity. The speed of a photon must remain constant. and for that to be true the speed must be relative to the size of the grid. No, I'll try to restate. C is constant. See below. a "scaled inch" is an inch in a scaled metric system (imperial system) or if you prefer it is an "expanded inch" in an "expanded metric". Yes, scaling=metric expansion but scaling has a wider meaning : it can be both expansion or contraction. when c=m/s in one system, then C=M/S in the second system If space only is scaled by two then we have M=2m and s=S (because time is not scaled)

I don't think it is that simple. When the road grows by 2 inches, it means that there is scale factor of 2. When the scale factor is applied to space, it is applied also to any velocity (because velocity is spce/time), and thus it is applied to C also. That's why we observe galaxies receding at apparent speed multiple of C. Or: if the road is 10 inches long, one inch travel is 10% of the road. When suddenly the road extends to 20 inches long (by scaling), then one "scaled-inch" still is 10% of the length, or 2 inches. The important thing is that for the same time, the distance as measured in the new space system (the scaled-space) remains constant: that's the main property of C.

That's a blank made of 20 letters. What an achievement.

If i understand Tar's idea: You are not alone running at 10mph. Some billions years ago, some other husband was running away in your wife 's direction, and your wife hasn't reach this husband yet. that is because following the standard model, we were all created at the same time (the Big Bang).

The bold part is totally wrong. There is no "other side of the universe", you are confused by the raisin cake analogy. There is no center and thus there is no "other side". When we look around us to the universe, all that we observe is in the past. There is no point (not even theoretically) where observation goes inverse back into the present. There is no physical mean to observe the future.

I wonder whether the 'habitable zone" on the diagram is the result of calculations or the result of pure observation and extrapolation.

I can't believe you guys. I think my concept is quite clear. I thought it was evident (i was wrong about that) My concept is that there is no reason to suppose that we are living a "special" period of the universe. The other concept (yours) that people in the far future will observe a different universe, and take wrong conclusions from it, seems complete bogus to me. Not to say ridiculous. At the moment we are speaking about a Spacetime continuum, what we ought to consider logical to space (the cosmological principle) must also count for time. It looks to me evident that an E,T, on another star of another Galaxy, anywhere else, at any time, should observe something roughly the same as what we are observing from here today. That means an E.T. billions of years in the past, and an E.T. (or H.B.) billions of year in the future. That's what I call the extended cosmological principle. The other cosmological principle, the one we all agree upon, assembled with current cosmology, literally states that only the observers at the same cosmological time with us are observing the same universe than we do. That is in some "cosmological present earth time". Following current cosmology, all other observer should observe some other universe, younger or older So, a standard cosmologist should correct the cosmological principle by stating that 'Viewed on a sufficiently large scale, THAT BELONG TO EARTH PRESENT TIME" (capital letters added by me). See wiki If you are a fervent supporter of the cosmological principle (as i am), you don't want to add anything to it. And if you add nothing to the cosmological principle, you must reach the conclusion that "the properties of the Universe are the same for all observers", either left, right, close or far away, yesterday and tomorrow.

Taking your example, what Krauss says is that in a few billion years, a man in the future will observe only the roof because the ground floor will have get out of observation, and that around the building only void will exist. Krauss says also that the man in the future will be wrong, and that we are right.

You're accusing Krauss of hubris for this analysis? I think you may have missed his point. I'd like to point out for the third time in this thread that indeed Krauss eplanation is a direct result of our current cosmologic model, and that the conclusion that "they will derive a picture of the universe which is completely wrong!" should ring a bell and indicate that we are wrong, and not that we are right and some people in the future will be wrong.

"rare people" That's very disappointing. -------------- I didn't notice you were sentenced for a post in this thread.

Wrong question. In this case the Columbus egg is: What makes you think it started? (except thousands of books, scientists, cosmologists, millions Christian believers, billions Muslims, etc.) The "start" concept comes from our understanding of living creatures (birth), and not from our observation of the physical world. Observation & experimentation shows that energy is conserved. You need incredible intellectual masturbation to ejaculate the concept of energy creation. It is not something observable. Everything shows that energy creation (from nothing) is wrong. But our preconception of "creation" is so strong that it eradicates any other logical approach. IMHO of course. And also our understanding of the concept of Time is still in its infancy.

Oh no, are you THE world renowned Christos Tsolkas? For info use google translate, I found no page in English http://frikipaideia.wikia.com/wiki/%CE%A7%CF%81%CE%AE%CF%83%CF%84%CE%BF%CF%82_%CE%A4%CF%83%CF%8C%CE%BB%CE%BA%CE%B1%CF%82 Here you are http://mirror.uncyc.org/wiki/Tsolkas See also here from SFN. ; http://www.scienceforums.net/topic/62806-mercury-perihelion-precission/page__p__649306__hl__tsolkas__fromsearch__1#entry649306

No help. I have trouble understanding even simpler things. For example Take a line: it extends to the left till infinite, and to the right till infinite. Now cut the line in 2 parts: you get 2 segments. One of these 2 segments extends to the right till infinite. The segment is thus infinite. But you have one end of the infinite in your hand (that's the point where you have cut the line). So you have an infinite segment that has a beginning. Or an end. I just try to explain something I cannot understand.

I went to the beach. My souvenirs are sand in my shoes.

Sorry to be so late: happy birthday. Cap'n you should complain, SFN is not on this site.

The point is about "evolving". From Wiki: The bold part in the quote is an assumption, it is not a "proven scientific fact".

I agree completely with the above. And disagree with the above. If the universe "must appear to be homogeneous and isotropic to an observer at all times in the future and the past", then it is consistent with my previous statement that says: "It is not conceivable (IMHO) that we currently live a privileged period of the Universe, a period so special that allows us to observe the Universe in a different way than future generations on future planets would observe. To me, there MUST be nothing special in our position in space (cf cosmological principle) and in time: IOW there is no privilege to our position in spacetime."