michel123456

Brian Greene's Elegant Universe in not free online. Only some summary here. "Chapter 13: Black Holes: A String/M-Theory Perspective Greene makes an unlikely comparison between black holes and elementary particles. Both, he says, have an internal structure that physicists have yet to identify. It has recently been suggested that an even greater similarity exists: perhaps black holes are actually huge elementary particles. After all, Einstein set no minimum limit on the mass of a black hole. Therefore, if we crushed a chunk of matter into ever-smaller black holes, the result would be an object no different from an elementary particle. This is because both are defined by their mass, force charges, and spin."

Fascinating thread. going too fast for the time i can spend here. From post #156 on page 8 If t'=0 then I suppose x=t'v=0 also.

1. A point like particle is described as such in 3D space. In spacetime it is supposed to be a line. So one could say that a point like particle is the section of a line at any instant in time. If one cuts the section with a blade of zero width, in zero time, it should not be a surprise if one finds nothing. 2. A line could be a vector. That is a line with an arrow indicating direction. Since in this specific case the line is the result of Time it appears that the direction of the arrow is the direction of Time. And thus we get from observation a lot of electrons that are following naturally the arrow of time. From that point and after you have forbid to continue the conversation about reversing time. 3. IIRC there is a very interesting point raised by Brian Greene that compares the properties of an elementary particle to the properties of a Black Hole. Mind blowing. I'll have to dig a bit.

1. So far, i haven't seen Md or Iggy or Delta take some understanding on xyzt's point that when the proper time of B's clock is transfered to C's clock then the paradox falls apart. There is no paradox anymore and xyzt is right. 2. Also I have not seen from Md Iggy and delta some understanding that in order to keep the paradox, when C takes the reading of B's clock, the traveler must say "what a crap, this reading is wrong, mine is correct" and C to continue with it's own reading, because B and C times do not correspond to each other: there is a jump as if B & C met in a place of spacetime where observations all around differ, the one observing on Earth the 2000 Olympics in Sidney while the other observes the 2004 in Athens. When B & C correspond, both observing Sidney, then we go back to point 1 and there is no paradox. In this case C must say, "my wrong, I am dreaming, I do not observe Athens (although he does), lets keep B's time and observe Sidney this is bogus."

Extracting the bold part from the quote, you stated: Then, when B and C meet, B can say "I have aged 1 year, while A has aged 0.5 years," but C will say "I agree B has aged 1 year, but A has aged 3.5 years since B left it." My comment is: It is not what the say, it is what they see, what they observe. During the experiment all observers are constantly in reach of sight from each other. It is not a situation where observers close their eyes during the travel and open it when they meet someone. Observation and measurement are the same all along the travel. IOW B sees A in June 2000 and C sees A in June 2003. from the same point, from the same instant. To me that is not correct: what they observe accounts for the delay of light, exactly as what they measure accounts for the delay of light. Observation and measurement coincide.

No, what I ment is that at the turning point, B looks back at the Earth and observes that the Earth is 6 LY away. C also looks at the Earth from the same point and at the same moment and sees the Earth is indeed 6 LY away. With the only difference that B sees the Earth in 2000 (say) and C sees the Earth in 2004!(say). And it is not a question of clocks anymore, they observe different things! Which makes no sense. The only way to make it somehow sensible is to change the straight path lines (in a spacetime diagram) with smooth curves, which mean "acceleration".

You all: I'd like to know 1. In a regular twin experiment, where the turnaround is made instantaneously, what is the observation of B a second before the turn and a second after the turn? 2. In Md65536 's experiment, what is the observation of C one second after the passing of info from B?

They agree what? That they disagree about their age in comformity with Relativity? (Edit) I am really glad to hear that "The twin paradox does not exist if there is no acceleration".

Well the twin paradox is usually presented as a situation where all observers are in an inertial Frame Of Reference. Or maybe that's me who understand things that way, but as it looks in the other thread about acceleration, I am not alone reading the twin paradox that way. Your section of Wiki begins with this: where evidently you consider that the traveler is NOT in an Inertial FOR. That is all the question. And if you are correct on this, you are correct all the way long. After much thinking and following the other thread, yes you must be right. IMHO of course.

Yes, You are correct. By transfering from B to C the exact same reading, there is no gap of time between B & C. For the gap, see here and here down the page.

It looks like you have an alternative explanation.

Yes. And that happens 3 times in the paradox.

I am grateful that you took so much time in explaining those things. Thank you. 1. o.k. 2. You are doing great! 3. I am ok with your new example but the first diagrams were with 12,5 time and 7.5 distance from Earth. Something that you reintroduce in your last diagram at the end (see point 6). To me what the Earth observes in term of distances & time is different from what the projectile observes. The diagrams should not be symmetric, see point 4 & point 6. 4. I understand the principle of reciprocity of velocity but maybe not the same way as you do. Velocity 6LY/10Y is the same as 7.5LY/12.5Y = 0,6C. observers on Earth and on the projectile observe different times and distances but according to the same ratio. Since the ratio in question is what we call velocity, both observers measure the same velocity. It does not mean that they observe the same distances and the same times. Also I do not understand why the black point (junction between comet & projectile) does not correspond to point 10 on Earth's line. I made a slight change to your diagram, see below. 5. I understand that the observer on the projectile does not move relative to itself. But as he sees the Earth receding, he sees the comet approaching at exactly the same rate. The Earth and the comet are in the same FOR in the example. 6. here below your diagram with Earth at 12.5 time and 7.5 distance. One can draw a vertical line from 6 red to 10 red, showing the Comet. what observes the projectile is different from what the Earth observes, the velocity is the same though. Your last diagrams are not symmetric so I think that at the end we do not disagree. --------------------------------------------------------------------------------------------------------------------------------- Here below are your diagrams again with some of my intervention. Hoping not to be too mistaken: -------------------------------------------------------------------------------------------------------------------------------- 7. Here I made a scaling of 2 4 6 labeling in order to obtain a correspondance between the intersection points. The result shows as a deformed rectangle (a rhombus). 8. Here I simply added the Comet line, which is parallel to Earth line. 9. Here it gets tricky: The left diagram is the same as above. The right is the precedent right one, rotated so that the Earth & Comet lines become vertical, and scaled so that the 2 diagrams can superpose. And the 2 diagrams do superpose without any almost trouble: the ship line at left corresponds to the ship line at right. Same inclination, same dimension. Except that the "Light" line does not correspond anymore. And that is ennoying.

You showed how to get v (seemed a bit complicated for me). You still must find t. I suggested that v would be that of a falling cylinder of 1 mm diam and height of the cone. If that is correct you need the formulas for a falling body and for the volume of a cone & the volume of a cylinder. ------------------ The other solution is to say that the melting chocolate will make a crust on the top and nothing will go down.

I don't get it. Where you label "Earth" I suppose you mean "Earth's time" Where you label "ship" I suppose you mean "Ship's time" 1. I don't see a line joining "ship's time" with "ship's distance". 2. I don't understand the thin diagonal lines joining point 8 on Earth's time with point 10 on Ship's time. I don't even get this one below. You stated that "the ship is at rest", but that happens only when the ship stops at the return point, when both the ship and Earth are in the same FOR. While the ship is moving the things as observed by the ship should show differently. For the moving ship, distance is less and time is less too. No? It should show 10 years on the time axis instead of 12.5, and 6 lightyears on the distance axis instead of 7.5

There will be no politicians floating in space, hopefully

It was a UFO with teeth http://www.dailyrecord.co.uk/news/weird-news/helium-shark-could-ufo-pilots-1864901

I am not an advocate of the BBT. Most, if not all defensors of the BBT support the idea that the Big Bang happened everywhere. However even an eminent scientist like Alan Guth the father of the Inflation Theory is embarrassed when asked the question of the "tiny original particle". See the below, at the end of part three.

As Iggy stated, that is the straight path. See the followings On the left is the A diagram as observed from the Earth, on the right the B diagram as observed by the moving one. The axis are orthogonal in both cases because both observe things as inertial observers. In fact the right diagram is almost a perfect scaling of the left one at 1,25 scale factor. The main difference between the 2 graphs is that on diagram A the spacing of the dots on the diagonal correspond to nothing, while on diagram B the spacing correspond to the time axis. Now, I tried to put the B diagram upon the A without great success. Here below is a try where the new axes are not orthogonal anymore, the bisect line is not 45 degrees. But the projection on the axes is perpendicular. Then I tried as explained in Iggy's link but it doesn't work well. The bisect of the new axes intersects point R and is never at 45 degrees (the bold line)

Right. Then it must be the sum of falling spaghettis each one with length the height of the cone.

Exactly, it is mixing frames, like in the following graphs.

Its been a long time I have to deal with stuff like this but i think the question is equivalent to calculate the time taken by a cylinder of 1 mm diameter and height such that it equals the volume of the cone. Having find the length of that "spaghetti", one can find the time as it was a falling object.

(emphasize mine) The current Big Bang Theory states that the things in the Universe appeared roughly where they are today. Dispersed everywhere. Not far away and not at a central point.

What I say is that none of your diagrams show the distance that the red has observed having traveled. From the red FOR, he didn't travel 7,5 LY (as pointed by Swansont).

Then the labeling 7.5LY counts only for Earth's FOR. For the traveler, the labeling should be much less (2.4 LY). That corresponds to a clockwise rotation of the X axis. Then i suppose the Y axis for the traveler should also rotate clockwise. And then signals as observed in the traveler's FOR should not be represented at 45 degrees in the diagram.