between3and26characterslon

Then you do not understand Relativity. Not all frames have relative motion, some have absolute motion. How can applying a force to A cause B to accelerate???

Ok didn't check my facts there, just remember hearing along time ago it would take something like 280 years. I still think though that ejecting stuff out the back of a space ship is not going to work for any manned interstellar flight You might like to watch this, particularly the last 5 mins which are all about space and time travel. http://www.youtube.com/watch?v=3zrGkiPJn5s&p=9A8A80BC2834046A&index=18

Don't know if that's directed at me Time slows down with velocity not acceleration. If for instance A is travelling faster than B then A will experience time slower relative to B. But it seems like people are saying that A and B have relative velocity and therefore they both see the same time dilation in each other. Then A accelerates and whilst A accelerates it experiences time at a slower rate compared to B. Then, when A stops accelerating and returns to uniform, albeit greater, speed, there is relative velocity between A and B again A and B see the same time dilation in each other again but both see A is now a little behind B. Is that what people are saying? If so they are mistaken. I'm not understanding how others here think relativity works, perhaps people can explain.

Will this change its wavelength?

What effect, if any, does this have on the photon?

I don't think any form propulsion that relies on throwing stuff out the back (ie rockets etc...) is going to get humans anywhere on an atronomical scale. It might get a probe out of our solar system a bit quicker than voyager but that's about it. If we ever get a grip on gravity, if we could generate gravity without needing mass to do it then we could gernerate a gravitational field in front of a ship and that ship would fall into the gravity well for as long as it's turned on. The rate of acceleration would be almost limitless because the gravity would affect everything in the ship equally, and could possibly achieve speeds near to 'c'. This is totaly science fiction though Any other form of propulsion would realistically have to be limited to an acceleration of 1g so that humans could live comfortably. So although our nearest star is 4.5 lightyears away, accelertating at 1g to near lightspeed turning round and decelerating at 1g it would take us about 280 years to get there.

Have a read here http://www.einstein-online.info/ So you (light) will end up (or stay) in your present but in travelling you have gone a year into the planets future. Let's say it's 2010 on Earth, it's also 2010 on this planet but when we look at this planet the year we see is 2009. If we send a message to this planet and it gets there infinitely fast then it arrives there in 2010 or 2011. Can you explain what happens here? I believe that special relativity says that you'll see most of its aging happen as you accelerate and decelerate I get the impression other people think this too, I think it's completely wrong. Take a look here http://www.einstein-...ights/TwinsRoad here's an extract "But how does this work - why is the acceleration so important? Did the travelling twin stay young because time went especially slowly for him during the acceleration phase? Not at all. In order to get a clearer picture, consider the following analogy that is not about time intervals, but about distances in space."

If different regions in space were fluctuating like you describe then there would probably be some observable evidence. I don't think there is any. If the entire universe was fluctuating like you describe then it would also affect any instruments you use so they would not detect this fluctuating time. In essence time could be fluctuating but it would have no consequence. You will still experience time at the rate of 1 second per second. And that's before we even get to what 'normal' time is which, I'm sure you can see, has no meaning. Or the fact (if it is a fact?) you would only observe this fluctuation from outside of the universe whatever 'outside of the universe' means.

If you were traveling very fast everyone else would see your time going slow but you would see your time as normal, if you were in a very strong gravitational field everyone else would also see your time going slow and again you would experience your time as normal. So, to answer your question, yes, when your time changes you will have no knowledge of it. If you were God for example looking into the universe and you hit the fastforward button to get to an interesting bit and then hit slowmo so you can enjoy one of your supernovae going off the time would be fluctuating but we would not know.

I think I got it now. You're saying that light will travel one lightyear instantly but in doing so it will travel one year into the future so it still appears to have traveled at the speed of light. Is that right?

Are you saying that time dilation only occurs in an accelerating frame?

Can you give some explanation here because that makes no sense to me (not saying it's wrong, just makes no sense to me). Wouldn't that mean its wavelength is changed by being reflected? As I understand it when a photon is absorbed its energy converts into kinetic energy but when it's reflected there is no transfer of energy. Like in those little glass vacuum jars with the black and white sails in them.

can you see an object 1 lightyear away as it was 2 years ago? yes can you see an object 2 lightyears away as it was 1 year ago? no

Swansont I will read Michel For example (how I like this question), can you see an object 1 lightyear away as it was 2 years ago? I don't know

vuquta I think you're over complicating things. As viewed from the embankment both flashes occur at the ends of the train at the precise moment M and M' coincide. In the time it takes light, from the front of the train, to reach M' the train has moved nearer to the flash, at the front of the train, and so M' will see that one first, simply because the light has travelled less distance. So like you say he will measure the speed of light as being faster because it has travelled, from his point of view, the length of the train in less time, only he won't because of time dilation and length contraction which will exactly compensate (he can't see the train is shorter or his seconds are longer). He will see both flashes occur equidistant from him, he will measure the speed of light as c but he will see one flash before the other. Which is basically another way of saying what Janus said.

Going back to an earlier argument. There is no absolute rest frame in the universe because, as was said, that would violate the principle of relativity. However an inertial frame that is moving with uniform retilinear translation with respect to all other inertial frames is no different to being at rest, it's the same thing. For this reason, even though coordinate system K is moving relative to all other coordinate systems, objects A and B are at rest relative to K so motion and rest are absolute within K. Whilst at rest A and B have their own coordinate systems which are inertial but when A is accelerated its coordinate system is no longer inertial. I found this which explains better than I can. http://www.einstein-...ights/TwinsRoad EDIT: As for the ladders I misunderstood the scenario

I completely admit I may not have all the facts but there is nothing wrong in challenging established theory. I am not going to believe something just because I'm told, I can only believe something when it makes sense to me and at the moment the expanding universe does not make sense as I understand it. Therefore I will ask and try to explain my confusion and hopefully reach a better understanding. Not all the experts are agreeable with the theory (most maybe, but not all) and I'm not dissenting, I just said that to be dramatic. Are you smarter or more knowledgeable than they are? I haven't ruled out the possibility What I'm struggling with is this If an object is 1 lightyear away you are seeing it as it was one year ago (just to keep things simple) 1 lightyears away = 1 years ago = speed x 2 lightyears away = 2 years ago = speed 2x 4 lightyears away = 4 years ago = speed 4x Based on that if we are looking at someting twice as far away we are seeing it as it was twice as long ago. If we see objects were travelling faster longer ago than objects are nearer to the present then they are slowing down with time not speeding up. Basically Hubble's graph plotted speed against distance and had a "/" slope but if you plot distance against time then from our point of view time would run from -13.7bn to 0 and the graph would have a "\" slope, this would show speed decrease with time. Could you not then change your time values to 0=the big bang and +13.7bn=today and you would still have the same slope on your graph. If I can draw a graph and paste it here I will.

1,2 and 3) are all correct if B does not accellerate, C is acting as the rest frame and B and C are motionless relative to each other. I think the problem is you're thinking if A has (v) relative to B then B has (v) relative to A and I'm saying this is wrong. This leads you to the opinion that the will both see each other as time dilated (as you said above) and this is wrong (as I understand it) To simplify the problem without altering the effects A accelerates (instantly) to (v) travels at (v) for one second and then decelerates (instantly) to rest again. Here's the logic A and B are motionless relative to each other (the principle of relativity says nothing is absolutely motionless BUT two things can be absolutely motionless relative to each other) Now construct a frame around A and B which is absolutely at rest relative to A and B (constructing this frame is just like using a ruler to measure something and it acts as a datum) Newtons law of inertia, a body at rest will remain at rest until acted upon by a force (it is essential you understand what this implies) A and B are at rest therefore no forces are acting upon them Apply a force to A and A only. A and A only accelerates. A and A only has (v) relative to the rest frame There is no force acting upon B so B is still motionless (law of inertia) Therefore A is absolutely in motion and B is absolutely at rest (within this frame of refference) A's time will slow down relative to the rest frame (the rest frame is still at rest because no force has been applied to it) B's time will be the same as the rest frame's because he is motionless relative to it (still no force applied to B) If A is experiencing time at a slower rate than B then for whose one second does he travel at (v) for He travels at (v) for one second of the rest frame (we measure against the rest frame) One second in the rest frame = one second of B's time (B is motionless relative to the rest frame), BUT One second in the rest frame < one second of A's time (A is moving relative to the rest frame) So if B experiences one full second, A (whose time is slower), has not experienced one full second yet and if A experiences one full second, B (whose time is faster), has experienced more than one second They will both agree A is younger They will both agree B is older They will disagree by how much A is younger They will disagree by how much B is older Somebody posted the ladder paradox (may have been you??) but the paradox does not exist. It comes from a misunderstanding of the theory of relativity. In this paradox the ladder is both longer and shorter than the garrage and the garrage is both longer and shorter than the ladder. Nonsense If you apply a force to the ladder then the ladder IS moving. As viewed from the garrage the ladder will appear shorter. As viewed from the ladder the garrage will appear longer. If the ladder remains at rest (ie no force applied) and you accelerate the garrage instead then As viewed form the ladder the garrage will be shorter and As viewed from the garrage the ladder will be longer

Are there any additives in the water ie. something to reduce the surface tension of the water and break up any bubbles Also won't you need to have a reasonable height of water in the vent so that when the heated water rises it can't just rise into the vent. The less dense hot water will just find the highest point but the height of water above it will push it round the system.

Thanks I've had a quick read but will carry on more thoroughly. I am reasonably familiar with the theory and it all made perfect sense to me until a few days ago when it occured to me that the further away something is the longer ago you are seeing it. This has the effect of reversing time so if something is expanding in -t it must be contracting in +t. When this thought happened the whole theory crumbled in my mind So I am left with 3 possibilities 1) I don't have all the necessary facts to understand the theory 2) I have all the facts but don't understand them 3) The theory is wrong You can see if 1 and 2 are true why I would think 3 is true I have had a look on the internet and found there are other dessenters among the ranks who don't believe in the expanding universe theory such as proponants of NRI (though this doesn't hold much appeal either) Something interesting I read though was that the expanding universe theory relies on (or implies) the wavelength of light increasing (frequency decreasing) over time and distance and therefore loosing energy whereas Einstein said the the frequency (and wavelength) of light is determined at emition and reception and therefore no loss of energy over time and distance.

1) For the purpose of relativity you have to construct an imaginary rest frame and call it (K) A is in a frame called (K') B is in a frame called (K'') (K') and (K'') are both in frame (K) (K) has time=t, distance=s and (x,y,z) (K') has time=t', distance=s' and (x',y',z') (K'') has time=t'', distance=s'' and (x'',y'',z'') The lorentz transformation will tell you how (K') and (K'') will appear as viewed from (K) when you know their (v) relative to (K) When you know how (K') and (K'') behave relative to (K) you can work out how t' and t'' behave relative to t then by knowing how (K') and (K'') behave relative to (K) you can work out how (K') and (K'') behave relative to each other and so how t' behaves relative to t'' Lets go back to the boats in the ocean boat 1 = (K') boat 2 = (K'') and longditude and lattitude(L&L)= (K) you measure boat 1's (v) relative to (L&L) that is you measure (K') relative to (K) you measure boat 2's (v) relative to (L&L) that is you measure (K'') relative to (K) so now you can work out boat 1's (v) relative to boat 2's, That is (K')'s (v) relative to (K'') It is only by knowing how A and B are behaving relative to (K) that you can know how A and B are behaving relative to each other. 2) "From the view of A, if B elapses 1 second, then A elapses 1/γ seconds." If B leaves 1 second later then whose second does he measure, his seconds are different to A's. does he leave one of A's seconds t'=1 or does he leave one of his seconds t''=1 bearing in mind (t'=t'' is false) He leaves 1 second t as measure in (K) becasue it is (K) we are measuring everything from whilst B is motionless relative to (K) he will have the same time as (K) whilst A in is motion relative to (K) he will have less time than (K) So B leaves one second (measured from K) after A but A thinks "hang on, that's not been a full second by my clock" So I think we are agreeing here if 1/γ seconds<1 second t They will both agree A is younger than B but they will disagree by how much A is younger. For arguements sake A will think he is less than 1 second younger, B will think A is more than one second younger and the difference will be exactly 1 second t (as measured in K) I will go back and read this thread again just to make sure we're on the same page (so to speak) but I think it applies to everything I've read so far that you need to construct an imaginary frame of refference and measure everything relative to that frame. That is entirely the point of relativity, if you do not create this frame of refference then you are disregarding the principle of relativity and the law of inertia which are the two axioms which you assume to be true for relativity to work otherwise it's like trying to measure something using an elastic tape measure.

Ok let me explain something here because I think people are missing something quite fundemental (apologies if you're not) (let me just say I'm not fantastically intelligent or knowledgeable but I am currently reading a book, it's called Relativity and it's written by a chap called Albert Einstein, if you don't know who he is google him) sarcasm! Anyway suppose you are on a small boat out in the middle of the Pacific ocean and there is no land visable. The water is moving at speed and in one direction under the boat. The wind is moving at a different speed and in a different direction to the water. Another boat comes past at a different speed and direction to both the wind and the water. You're at full throttle and moving at yet a different speed and direction. Questions 1) How fast are you going? 2) What direction are you going in? There is no meaning in these questions unless you construct a frame of reference with which to measure against, this is what we do and we call it longditude and lattitude. This frame is a pratically rigid structure and is considered to be absolutely at rest and all other velocities (water, wind, boats) are measured with respect to this frame. As there is nothing in nature that is absolutley at rest we have to construct an imaginary frame which, for the purposes of our experiment, we consider to be absolutely at rest. Going back to our friends A and B they are not at rest relative to each other, they are both at rest relative to a practically rigid structure, an imaginary framework of axes (x, y, z). This is a system of coordinates and we call it coordinate system (K) When A accelerates and aquires velocity (v) he does so relative to (K). It can now be considered that he is in his own system of coordinates and it is called coordinate system (K'). So now we consider that (K) is at rest and (K') is moving with velocity (v) relative to (K) (K) has time=t, distance=s and coordinates (x, y, z) (K') has time=t', distance=s' and coordinates (x', y', z') All the axes (x, y, z) and (x', y', z') are parralell (ie x is parralell to x', y to y' and z to z') and (+)positive in the same direction. This means that when using the Lorentz transformation you are seeing how (K') changes with respect to/as viewed from (K) If (K') is moving with velocity (v) in a (+)positive direction along the (x) axis of (K) then (K) is moving with velocity (v) in a (-)negative direction along the (x') axis of (K') This means when using the Lorentz transformation in (K) to measure changes in (K') (v) has a (+)value But when using the Lorentz transformation in (K') to measure changes in (K) (v) has a (-)value to indicate it is in the opposite direction. When A has (v) with respect to (K) he experiences time at a slower rate than (K) ie (t')<(t) (t' seconds are longer than t seconds) If B leaves 1 second (t) or <1 second (t') later and attains the same velocity as A then both A and B will consider A is younger There will be a difference between how much A and B think A is younger If B leaves 1 second (t) after A then A has not experienced 1 full second (t') yet (A) is younger because he is the first one to experience time at a slower rate. He will remain younger for as long as they both have constant (v). If A stops (relative to K) and B catches up to A and stops (relative to K) they will both be the same age again.

"Where you're going wrong is the fact you have not studied the links Martin has provided at the top." Could you copy and paste them cos I can't see them.

But there are bigger structures in space than superclusters. Superclusters themselves form bigger structures (at least that's according to Prof Stephen Hawking in his documentry 'Universe' on TV the other night) Otherwise what you're saying is there are discrete pockets of matter in the universe surrounded by huge expanses of empty space. The problem is that the distance that you need for space to expand is greater then the average distance between superclusters (that's an educated guess BTW). Also if A (a supercluster) is gravitationaly bound to B (another supercluster) and B to C and C to D and D to..... W and W to X then although A is not bound to X it still can not be that X is receding from A. Lets say for example that everything within 1bn lightyears from us is not receding from us Andromeda is less than 1bn lightyears away and is bound to The Milkyway there is another galaxy less than 1bn lightyears from Andromeda which is bound to Andromeda another galaxy less than 1bn lightyears from that one and so on So I still don't understand how everthing locally can be gravitationaly bound, that this is true wherever you are in the universe and yet the most distant objects are receding form us which is also true wherever you are in the universe. What does make sense (to me) is that soon after the big bang galaxies were moving faster than they were longer after the big bang. When we look at distant galaxies we are seeing them as they were soon after the big bang. When we look at nearer galaxies we are seeing them longer after the big bang and they are moving slower. Imagine you have 1000 big white balls and you place them receding form you in a straight line 1mn lightyears apart so that the one furthest from you is 1bn lightyears away. Now you suddenly expand the space between them. You would not see them all move at once you would observe a wave of movement propagate along the line of balls. It would take 1bn years before you would see the furthest one move. If before the information that the furthest ball has moved had reached you, the distance between the balls suddenly decreased, you would observe a wave of nearby balls getting closer but you would still observe the distant balls receding from you. Although the distant balls have moved closer to you again this information has not reached you yet. Sticking with our white balls, they are all identical in every way, especially mass. Due to their mass they will all attract each other and the gaps between them will reduce equally. Yet due to the expansion of space the two end balls get further away from each other. From your observation point at one end of the line you will see nearby balls getting closer to you and the most distant balls getting further away from you. It is therefore a necessary consequence that one ball somewhere along the line will appear to not move. It is moving towards you due to gravity exactly as much as it is moving away from you due to the expansion of space (if gravity is an acceleration and the universe is expanding at an accelerating rate the net acceleration on this ball will be zero). This will be directly proportional to the sum of masses acting on it and its distance from you. Again this does not make sense. At least, if this phenomenon is proportional to the sum of masses over distance then there must be a constant to describe it and that constant should tell you something. It still makes sense to me that the expansion of the universe is slowing down it just looks like it's expansion is speeding up because we're looking at the past. Where am I going wrong?

No, your right. My bad, I was assuming that v=c If v did =c and B left 1 second after A set off (that is one second t with respect to K) then both A and B would agree that A is 1 second t or less than 1 second t' younger than B. That is it will be t=1 seconds or t'<1 seconds before B sets off. But as v is not known then the time difference can only be given as a mathmetical expression and not as a numerical value.