michel123456

Did I? If I did I am really sorry. Quoting Spyman: Which means that the expanding distance in spacetime is NOT a velocity. I agree 100% with that. But then, why do we all accept velocity addition like this: (from the previous link http://arxiv.org/pdf/astro-ph/0310808v2.pdf) page 3. (bolded mine) You cannot add bananas & umbrellas. It is wrong. And the "ant on a rope" is NOT a good example because it is based on velocity addition.

It may be what I said, it may not, I am not sure. I am not even sure that light travels a "comoving distance". From Wiki: (bolded mine) I suppose the "distance" I am talking about is a distance along the path of light in expanding spacetime. It is not a distance at a specific time, it is a distance along time. ------- Anyway, it is very close to what I ment. ----------- (edit) your comment about unscaled time is basically what I ment, but it must be trickier. If one could imagine contracted time, then it could equalize expanded space and produce a result where the photon does not change state of motion at all: it could follow a straight geodesic. IIRC I have seen somewhere such a spacetime diagram. Am I wrong?

Hmm I am not sure. You have to interpret what you are measuring. In Imatfaal's analogy, everything happens in real time, one second. When observing the universe, nothing happens in real time. What we are observing is a pack of parallel rubber bands, each of one being extended at 1 sec time interval. The first band below is extended 1 sec late, the 2nd band is extended 2 sec late, the 3rd band 3 sec, etc. And not exactly that: we are observing the first dot on the first parallel band, the second dot on the 2nd parallel band, the 3rd dot on the 3rd band etc. That makes interpretation of measurement a little bit complicated.

Maybe you are confusing what appears to be and what is measured. In my example if you measure the car speed with a laser, you will get a correct standard speed.

(bolded mine) In this case you should be interested that any scaling up has this effect. It is caused by standard Euclidian geometry. Scale down has the contrary effect : the farther you see, the less it contracts. When you drive on the highway and look in the mirror, you see a car far away behind you that drives faster than you. You may wait a minute or 2 before the car comes close. Then suddenly the car passes by very quickly, zzzzouf. After that you see the car in front of you vanishing slowly and slowlier to the horizon. The object far away looks like moving slowly, the object close looks like moving fast. It is an effect of perspective which is nothing else than an everyday geometric contraction.

Right. Except that the dots are not dots anymore, they expanded together with the rubber band. What you should have done in order to represent the standard model is to stick pennies on the rubber band. Better, it should have been pennies with rubber band collated between them (no rubber between the pennies, or rubber not expanding beneath the penny). Here below what I understand: In this analogy, the penny is a galaxy cluster. What maintains the penny from expanding is what we call gravity. The material the rubber band is made of is unknown (as far as I know) The force that makes the rubber band expand is unknown (as far as I know) What glues the pennies to the rubber is unknown (as far as I know) and BTW what gravity is made of is also unknown (as far as I know) It is believed that the pennies don't move very much along the rubber band, they roughly stayed in place from the beginning of the Universe. IOW it is believed the pennies were created at the relative place they are today upon the rubber band. It is believed that a long time ago the rubber band had zero length. It is believed that in the future the rubber band will have infinite length. Tell me I have understood nothing.

Could someone split the thread from post #185 please. This diagram is a pure delight to comment.

It may be what I said, it may not, I am not sure. I am not even sure that light travels a "comoving distance". From Wiki: (bolded mine) I suppose the "distance" I am talking about is a distance along the path of light in expanding spacetime. It is not a distance at a specific time, it is a distance along time. ------- Anyway, it is very close to what I ment. ----------- (edit) your comment about unscaled time is basically what I ment, but it must be trickier. If one could imagine contracted time, then it could equalize expanded space and produce a result where the photon does not change state of motion at all: it could follow a straight geodesic. IIRC I have seen somewhere such a spacetime diagram.

I couldn't resist.

Yes. Agree. That's the distance as measured from the metric inside the "local penny". That is not the distance as measured from the expanded metric. Nobody here to slightly correct Wikipedia ? When the metric changes Light don't travel more distance, only the scale of everything has changed.

and it is wrong, when distances increase due to expansion it takes longer time for light to traverse this new distance. But distance do not increase due to expansion. The metric is scaled, that is entirely different. And that changes wavelength.

Keeping track today: Michel has 3,103 posts divided by rep 260= 11,934615384615384615384615384615 Hal has 585 posts divided by reputation -32 = -18,28125 Conclusions yours. But Hal has improved. (Hi Hal, are you here?)

If he is Questionposter and Steevey, then he has improved. And BTW I didn't like your first comment because it gives the impression that you are accusing the OP of receiving neg reputation that you yourself have given. Maybe that's only a bad impression, I don't know who gave the neg point to the OP, but since you are the first responding that's what I suspect. (edit) And i don't think it is accurate to say that: It must be a boutade.

(bolded mine) Maybe that is a supportable scientific POV but that is a politically incorrect. It opens the door wide to any sort of massacre. It should be better to say that we are all (all living things) very special.

Not to me. But there is not only death, there is also suffering which is worse in many cases IMHO.

The result is more important, or is it not? ...Maybe the dividends are more important, and glory.

(bolded mine) Why then did you put the "Speculations" down in the Forum's bottom (where it stinks), exactly above the waste disposal? You could upgrade the speculation entity: rename the existing "Speculation" into "My Pet Theory", and create four levels of speculations, at the top of the Forum. The first level for all members - at the risk of being throwned into MPT, a second level for speculations that resisted level 1 and experienced members (as you did for the religion forum)-at the same risk- , a third level for members who resisted level 2 for several weeks, and a fourth level only for V.I.P. (maybe upon invitation) Something like that. I bet this kind of organization would leave the speculation entity almost empty, and you would be very interested to read the lonely thread in speculation level 3.

Maybe the point of misunderstanding: From the right beginning, I am speaking about velocity of light in the expanding space (in the gap between the "local pennies"), NOT about velocity as measured inside the penny, or received at the penny.

Actually some time ago I thought naively that was the aim of a scientific forum...

(bolded mine) Yes you do. Taking as granted that C is NOT influenced by the scale factor: how is it possible to state that "Photons are not able to reach us when space between them and us is expanding faster than they can propagate"I'll let you think more about this point. I'll do the same. I quit this thread for a while.

(Bolded mine) But we can observe such objects, don't we? -------------------- edit And this sentence of yours: placed next to Iggy's look to contradict each other. If velocity "has absolutely nothing to do with the scale factor", then it has nothing to do with the scale factor. Point. Velocity cannot in the same model be influenced by the scale factor in such a way that "Photons are not able to reach us when space between them and us is expanding faster than they can propagate".

Spy, your analogy uses velocity addition. Photons (not boats) always reach us at C, no matter what. When a light source comes towards us at 99,99% of C, the photons from this source reach us at C. When a light source goes away from us at 99,99% of C, the photons from this source reach us at C. And I guess that from a hypothetical source that goes away from us at 5000000000000000 times C (for any reason), the photons from this source reach us at C. No matter what. That's what "no matter what" means. And the concept itself of a photon receding from us because the source is getting away from us transported by space expansion, this idea is very peculiar. It looks like a photon going away from me, me being the source and not the receptor.

(bolded mine) You mean velocity (of a photon) is constant.

Right. What about the velocity?

Yes obviously I miss something. Isn't it correct that light "stretches" when space expands?