michel123456

A way to avoid conceptual problems is to consider the "discrete" concept as relative, not absolute. That is not the way established science works. Although the "everything is relative" expression is widely used, when talking about dimensions, it is considered there exist a smallest absolute distance, the planck length. As far as i can understand (but many people here say I understand all wrong), there is no absolute smallest distance, but only relative smallest distance. So that the smallest "piece of space" must also be relative.

"An orbit is the gravitationally curved path of one object around a point or another body, for example the gravitational orbit of a planet around a star" (from Wiki). Under attraction, the naive point of vue is that bodies will bump. Newton made a hard job on demonstrating that bodies falling to each other will not necesseraly bump, but orbit. Under gravity, which is attractive. Well, I was wondering, based on the general symmetry of physical laws, if under repulsive action, maybe the naive picture of bodies expelling each other away was right, or do they orbit ? I couldn't find anything non-symmetric in the laws of motion. So I deduced that under repulsive force, objects must orbit too. Right?

In My Humble Opinion (IMHO)

Yes. They will measure different distances & times. I agree on that. But what they will measure will not be "real". When thousands of different observers are observing one single phenomena, they will all disagree on what they measure. From that fact I conclude that what one observer will measure cannot be considered as "really happening". I conclude that what one observer will measure is a deformation of what really happens. And all thousands observers will all measure different deformations of one single undeformed reality. Look: You believe I am contradicting, I believe you are contradicting. It is useless to continue that way. I will make a pause and rethink the subject. I suggest you do the same.

I agree with Ashish's interrogation. Field is a widely used concept. But if you think very (very) deeply about the concept, it is pure mystery. A field is like an aura of knowledge around an object. The object "feels" something when it is in the range of "feeling" of another object, and is attracted through action at distance. But physics is not about "feelings" so it calls that a field. And action at distance has been accepted without any trouble, although without tangible explanation. IMHO it's all still unexplained stuff. IMHO, and under all reservations, if you want my point of vue about what a field is, I have come to the conclusion that a field is nothing else but the object itself, i.e. that the Earth is not the globe only , but the globe + its field (gravitational) extended all around (until infinite). The "what is it made of" is another question. Not the right question actually. The right question is "what was it made of", because a field is extending in space & in time, and is always in the past of an object. This must be a clue.

It is not a language barrier. It is a conceptual barrier. For me, if reality is frame-dependent, (and I surely agree on this) length contraction & time dilation cannot be a real phenomenon. Merged post follows: Consecutive posts merged The "objective measurement that all will agree on" is the one which coincides with the FOR of the observed phenomena. It is the one we choose for determining the rest mass.

Language barrier? Physically happens, is really happening, pragmatically, Reality, fact, occurence.

How many atoms do you need to get temperature? two?

What is your interpretation when the apple falls from the table?

Maybe. But you believe contracting of distance really physically happens.

No. There is no preferential referential frame. Earth's FOR is not THE referential frame. The traveler is at rest in his own FOR. He believes he is the absolute FOR and decide that the ruler on Earth is contracting, and that time on Earth is under dilation. Your descriptions are just as like we knew which one is traveling and which one is at rest. We don't know that. Merged post follows: Consecutive posts merged That is very worrying.

No. On the left side , there is the "hand part", corresponding to the original impulse. On the right side, there is the "gravity part". Time is running from left to right. If you reverse time, going from right to left, there will still be 2 parts. In exactly the same position. The "gravity part" will be on the right side, and the "hand part" on the left. The "hand part" will not vanish. The "hand part" will attract the apple through some eslupmi (the mysterious inverse of impulse).

Emphasis mine. So you really believe contraction is really happening. If speed is relative, and you agreed about that, contraction is relative too. The traveler is as good observator as anyone else. The traveler observes that on Earth the distances are contracted. ...... I can't do anything else for you Swansont. You have to unscrew something in your brain by yourself. I can't do that for you. At the antipods, people observe imaginary roads.

In the rocket frame, the length is not contracted. The length is contracted as seen from another FOR. The traveler notices nothing, the lengths are measured by him as we do here on Earth: he doesn't know whether lengths are contracted or not. And you accepted inconsciously that speed increases. The event "traveling" is measured differently from different observers. Relativity is the Theory that permits to calculate what each observer will measure. The one will see lengths contracting, the other will not, according to their relative displacement. None of the observers knows the truth. It's all about how one observer sees the other. It's all about observation. When we observe a traveler at speed near to c, we observe his mass increasing. Reversely, the traveler looks at us and observes that our mass is increasing. What is happening? Does our mass increase because we sent some fellow to another galaxy? I don't think so. It is only deformed observation, ruled by Relativity. As an analogy, think of the deformations caused by perspective. It is possible to build a geometrical theory that will assume that the edges of a road join at horizon, and make that theory work in any circumstance. In this theory, the distance to horizon would always be the same for all observators. No matter the velocity, the distance to horizon is a constant. But do the edges of the road really coincide at horizon, or are they parallel? Where is reality, and where is observation?

No. That is not necessary. Relativity is right. Relativity states that SOL is constant. I can keep that. If bold characters mean shouting, you must be pissed off. Sorry. Merged post follows: Consecutive posts merged O.K. Forget the FTL. Take a STL (Slower TL) object going away (not receding) at 0,9c. Can we see it? And what is the speed of light coming from this object and reaching us ? I couldn't find a more stupid question.

Equations show in the grey area labeled "formula" right above the A B C D columns, when you tick a number in the spreadsheet. ____________________ Sometimes, I feel tired with all this. 1.We all agree that speed is relative. 2.We all agree that a traveller won't see his own mass change, no matter what speed. Of course because speed is relative.see (1) What else do you want to understand that nothing can physically prevent the traveller from going faster? Of course because "going faster" is relative. see (1) What is wrong in this? Am I totally out of logic or are you all completely stuck ?

Spyman, I followed half your post, I think you 're right (the other half about twins doesn't interest me). Here is a spreadsheet not made by me, but by another member (nicknamed Jerrywickey) on another Forum. He is examining a spaceship leaving the Earth under constant acceleration 1g, and what happens for observers on Earth & on the spaceship. http://spreadsheets.google.com/ccc?key=0AkfQmC4TTWCQdGpUcXlYR0U2ckowal9aZW96TTRDVWc&hl=en#gid=0. No one (on the other Forum) was able (or interested) to check his numbers. From the original OP "250 days after leaving, the travelers perceive they have exceeded the speed of light (1). The travelers will be slightly more than 0.29 light years from Earth. 278 days will have passed on Earth; and an Earth bound observer measures the travelers speed at only 71% c After 556 days pass on Earth, observers on Earth will measure the travelers speed as very near light speed. The travelers will be 1 light year from Earth at this time. Only 353 days will have passed for the travelers who are measuring their speed at what appears to them to be ever increasing multiples of light speed, hundreds and thousands of times the speed of light because time is passing more slowly for them, of course. Each second that passes for the travelers on day 353 increases the speed at which they perceive themselves exponentially. They travel until they reach half the distance to their destination. No matter how far that distance is, the next star or the other side of the universe, they will reach that middle point sometime on day 353 or just hours into day 354, at which time they turn the thrust of the ship around to begin slowing down at 1 g. In another 353 days they will arrive at their destination. 556 days on Earth and at their destination will pass during the traveler's 353 day acceleration and another 556 days will pass during their 353 day deceleration, but any number of years, centuries or millennia will pass during the 353rd and 354th traveler day as they cruise through space at incrementally increasing relativistic speeds. Of course while we have the nuclear power off the shelf and we have the ability to build such a space ship, even a single free atom in space striking the space ship at relativistic speeds would impart catastrophic energies which would destroy the space ship instantly. But I was hoping someone might be able to check my numbers. I am using SQR(1-v^2) as the relativistic transform and you will find the ship's speed from both the observer at rest and the ship's frame of reference on a second by second basis for each day at http://spreadsheets.google.com/ccc?key=0AkfQmC4TTWCQdGpUcXlYR0U2ckowal9aZW96TTRDVWc&hl=en#gid=0. Jerry" You can make a quick check looking at the chart inside the spreadsheet. The interesting values are at the end of the spreadsheet. There is no other way than checking by yourself. It is Relativity in application, not a new theory. (1) the "perceive" is made by triangulation with some reference stars.

Something like that. For some logical reason, most existing models are one-way style. They begin somewhere, they end somewhere (or they don't end at all), at the image of the number line, going from zero to infinity. Some models try to extend the situation by introducing a backward motion, from infinity to zero, and then again forward, at the image of a piston engine. IMHO, the only logical model must be cyclical, not back and forth, but always in the same direction. We need a circular model where the small matryoshka doll gets somehow bigger and swallows the first one. Something like the snake that eats its tail, the ouroboros. You can begin to wonder, because I am not aware of the existence of such kind of model. There is work to be done.

I beg you don't go into the twin paradox again. Merged post follows: Consecutive posts merged The entire Theory of Relativity is based upon an axiom that comes from observation. SR & GR are theories of observation: they start from observation, they end to observation (as any decent Theory must do). SR & Gr are absolutely right, correct. But they still are about observation. If you decide to move, it will not change the physical behaviour of a galaxy light years away. Speed is relative. Crudely, you can masturbate as long as you want, I will not feel orgasm. And what you observe is not necesseraly what happens.

That's your answer Moon. In other words, nothing forbids you to accelerate, independently of your velocity. It is really easy to understand, because velocity is relative. Relative. Relative. (I have to say it 3 times like at church, to be sure the disciples hear the sermon). What will another observator measure, from another FOR has absolutely no effect on you. This other fellow will measure your (relativistic) mass increase, but that is only a relative observation. Nothing bizarre will happen to you. The only bizarre effect is that if (hypothetically) you pass the speed of light relatively to some observator, this other fellow will measure that you will not have pass SOL. And reversely, you also, measuring the same velocity from the other side, you will also measure that the other fellow's velocity relative to you is less than SOL: that is the reason why scientists say that it is impossible to go FTL. Not because something physically cuts your speed, as commonly believed, but because it is impossible to observe directly. Amen.

I won't put any theory. Just a simple remark. "beginning" is an hypothesis by itself. And a dangerous hypothesis because it goes against all observations. If you rely strictly on observations, and on laws of physics, you must admit that Energy (and matter) cannot be created from nothing. Ough, I already hear physics experts screaming. Sorry I couldn't stand. Mea culpa.

Is that a silly question?

Bis repetita placent. Post # 18 "Well, from the beginning of this thread, I am speaking about "objects moving away from one another" and not about "the amount of space in between them increasing", following this simple reasoning: Lets take an object moving away (not receding) at speed v < C. This objects emits light that we can see. The naive concept says that the photons that will reach us must have speed C-v= F. (1) But Relativity shows it is completely wrong. Photons are reaching us at C. Always. Now, when we take another hypothetical object moving away at v > C, we are used to make the same substraction, putting C-v= F (2) and obtaining negative F, meaning that the photons will go away from us instead of reaching us. IMO it is exactly the same error, because equation (1) is the same erroneous with equation (2). We simply cannot make the naive substraction, it is wrong. In any case, the photons will reach us at C." (text mine, emphasis mine) And the hypothetical FTL object is observable. and redshifted. Because if we assume the contrary, I would like you to explain me how it would be possible to have photons influenced by the relative speed of the (hypothetical) object.

And I say any can do.