gib65

I see what you mean about the satellites. In that sense, yes, both twins could have their clocks synchronized (I personally wouldn't call them Master Clocks though). Not moving with respect to whatever reference frame you've chosen. I take it as a general rule in relativity that if one says 'not moving' that means with respect to the chosen reference frame.

Ha! Or like I've said: "My car goes 300km!!!" as an expression of its speed.

Fair enough. And I'm sorry on my part for being snippy. I think we misinterpreted each other. I was adding something further to your comment and I think you interpreted that for a search for further answers (as though your comment didn't make sense). Your story is not invalid in the sense that you can posit that a Master Clock exists relative to which all other clocks' date=' insofar as they are moving relative to it, slow down. But this is only in virtue of choosing a reference frame in which the Master Clock is fixed. If we were to choose our reference frame such that the stay-at-home twin was fixed, then the Master Clock would be moving relative to it and tick slower. If we chose to consider the travelling-twin as fixed, both the Master Clock and the stay-at-home twin's clock would be running slower. Those who are just getting into relativity often have a hard time with accepting that there is no answer to the question "Okay, but really - who's [i']actually[/i] moving? Whose clock is really ticking slower?" The answer is, it depends. This can be difficult to grasp unless you get the principle of the relativity of simultaniety. According to that principle, it's certainly possible that in one reference frame, as one person's clock (who's fixed) approaches 2:00, a second person's clock (who's moving) approaches 1:00, and they both strike those hours simultaniously, but in a different reference frame, it's the exact opposite. The first person's clock (who's now considered moving) approaches 1:00 whereas the other's (who's now considered fixed) approach 2:00, and they both strike those hours simultaniously. If you can wrap your head around that concept, the rest of relativity is a breeze (as far as I'm concerned).

When did I ask this? I began this thread asking why SR was accepted without GR. Since then, I got my answer. I also asked a question about what the travelling twin would see if he constantly looked at his stay-at-home brother. I got my answer to that as well. My reply to your comment was simply to add something I felt was important for a full understanding of relativity. Dude, there is no 'actual'. That's the whole point of relativity. There are only relative states. The travelling twin isn't 'actually' travelling while the stay-at-home only 'appears' to be travelling from the point of view of the travelling twin. Both are actually travelling relative to the other. Einstein didn't just pull the term 'relativity' out of thin air. You're version's a little too simple. Did you even watch the videos I offered? That's because there was nothing wrong with your version. It was just incomplete. Actually, I find it quite intuitive. Good luck to you (you'll need a lot of it). Yes, each other.

When did they find this out? I thought Maxwell discovered this, and didn't he die before Michelson and Morley conducted their experiment?

Thanks ajb, but what is a "noncommutative nature to space-time"?

Well, we know matter can be divided until you reach its fundamental particles (electrons, quarks, whatever), and QM tells us that this is so for energy as well (photons). But then some go further and claim that QM shows spacetime to be composed of fundamental units as well. Usually, what they are refering to are the Planck units (like the Planck length, Planck time, etc.) - those measures of space and time for which we cannot measure anything smaller. But is this warranted? Is it warranted to say that these smallest units of measurement are 'particles' of space and time, that there is no amount of space or duration of time smaller than these amounts? Or is it just a matter of our ability to measure it?

Yes, that's what I meant. I appreciate the English translation. So Maxwell's equations do imply a constant c regardless of the speed of the one measuring it? Is this consistent with Michelson and Morley's expectations (that they could measure the speed of light differently depending on how they oriented their table)?

I'm not complicating anything. That's just the way the theory is. No, it just means neither one is accelerating. They could be going a different speeds though. Here's some good videos that explain SR: <-- simultaniety <-- time dilation The last minute and a half of the last video (starting at 7:30) stresses my point, but you should watch the whole thing because it's all relevant to understanding SR.

So what was the principle on which Einstein believed light travelled at c irrespective of the observer? Was it just common knowledge at the time? I ask because they say he never mentioned the Michelson-Morley experiment in his proposal of SR, and that to me is the prime source of such knowledge.

Is it true that you can increase your chance of having a boy or a girl depending on what time of the month you conceive? I was told that during one half of the woman's menstral cycle, her system is more hospitable to X sperms than Y sperms, and that during the other half, it's more hospitable to the Y sperms than the X sperms. Is there any truth to this, and if so which half of the cycle is which, and by how much do the odds increase/decrease?

Well, if you really want to get to the bottom of relativity, neither of the twins' clocks are going faster or slower than the other in any absolute sense, at least not when they are travelling at uniform velocity. Acceleration may be another matter. One of the first insights that lead Einstein to SR was the relativity (or non-existence?) of simultaneity. That is to say whether two events happen simultaniously or not depends on the observer and his speed relative to those events. So whether the one twin's clock strikes 1:00 simultaniously as the other's strikes 2:00 or visa-versa is not an absolute fact. It can legitimately be said that relative to one, 1:00 happens before 2:00 but relative to the other, 2:00 happens before 1:00. When the travelling twin turns around, he accelerates, and that constitutes a shifting in reference frames, which allows for any adjustment needed to compensate for the discordance between their temperals schisms.

That would be true from the point of view of the stay-at-home twin. But relativity says that from the your point of view, the stay-at-home twin is moving. So from your point of view, the stay-at-home twin's clock will appear to run slower.

Is it true that the mother will pass on her immunities to her child through the blood interface linking the plasenta to the womb? If this is true, do those immunities simply accumulate from generation to generation? Essentially, that would mean we should all be immune to things which our first human ancestors grew immune to within their lifetime. Does this make sense?

I know the question seems to make no sense, but I swear I've seen them. Twin siblings who look perfectly identical in every way except for their sex. If you've ever seen that show John and Kate Plus 8, you'll know what I mean. They have six-tuplets, 3 girls and 3 boys, and the girls look identical to each other and so do the boys. Can this ever happen?

Right, because it was a corpuscular theory. As soon as you switch to a wave theory, you need a medium. You need an ether.

Could it not hold a certain amount of energy at the beginning and release it later? Or is that not how it works?

Who first discovered c? Wasn't it Maxwell? Perhaps he wasn't the first to measure the speed of light (but I think he was), but I'm pretty sure he was the first to discover that c was a constant. What I'm actually wondering - my real question - is this: does the conclusion that c is constant - at least during Maxwell's time - necessarily imply that it is such irrespective of the observer (as entailed by relativity)? I ask this because it seems to me, based on my understand of the history of physics, that there was a contending theory to that of relativity which didn't require c to have its value irrespective of the observer. I'm talking, of course, of the ether theory. If you assume the ether is always fixed, then light can propagate through it at the constant c without requiring that every observer, regardless of his speed, measure it to be c relative to himself. So c would be a constant and you wouldn't need relativity. Further, it would explain why Michelson and Morley conducted their experiment, expecting as they did to find differences in the measured speed of light depending on the orientation of their table. I'm just wondering where Einstein got his inspiration from. I'm pretty sure he rejected the ether theory (and wasn't being too controversial in doing so since many were abandoning it at the time), and so he probably was lead to special relativity as the only conceivable alternative. Anyone know if I'm right about any of this?

I might as well spell out my purpose in asking these questions. I'm wondering whether something needs to interact directly with the electron in the double-slit experiment in order to collapse its wave structure into the more streamline structure it takes on as it passes through only one slit. I always assumed that any detection device you setup at the slit can only detect the presence of the electron by interacting or disturbing it, but a thought occurred to me the other day that the electron could emit a photon and that photon could interact with the detection device, effectively causing it to detect the electron's presence. This photon could be emitted spontaneously (i.e. it wouldn't necessarily have to be fired at the electron), and although we'd have to be extremely lucky to detect it, it could happen in principle. In that case, we'd be 'observing' the electron without actually interacting with it directly. They say that observation causes the electron to act like a particle, but in this case it seems almost 'magical' (or as they say 'spooky action at a distance'). I suppose you could invoke quantum entanglement to explain this - i.e. the electron is entangled with the photon it emits - and so for anything that happens to the photon (like interacting with the detection device), something will also happen to the electron (it will act like a particle). Is this how it might happen in actuality. Is entanglement the way a physicist would typically explain it?

So what happens in the double-slit experiment where they setup a detection device near one of the slits so that they can detect whether or not an electron passes through the slit? Does the decive attempt to fire photons at the electron or does it sit quietly waiting for the electron to fire a photon at it?

They say that in order to measure or detect an electron, a photon must be fired at it. But can an electron be measured or detected if the detection device simply receives a photon it spontaneously emits? I have a follow up question about this.

Is that at all points of accerelation (including deceleration) or just one in particular (like when he first leaves Unprime or when he begins his return trip)?

Thanks D H. I focused mainly on phys.vt.edu (the one that refers to Prime and Unprime), and I think I understand. It has to do with switching reference frames. When you do that, all bets are off for simultaniety. What would happen in the following scenario? Suppose Prime had super-human vision and was able to observe Unprime at all points in his round trip. He never travels faster than light so all light emitted by Unprime should be able to reach him and his eye receive it. What would Prime observe if he were to constantly look at Unprime? I understand from the website that "Prime notices that Unprime's watch is running slowly" as he first experiences uniform velocity away from Unprime (just after accelerating). So he would at first observe Unprime to be aging more slowly as well - right? I assume this is what he would observe on his return trip as well (during uniform velocity). The website also says that "Once Prime stopped at the distant station, he rejoined Unprime's frame of reference: Prime saw all the clocks in that frame to be synchronized again (but reading 1.25 years, while his own watch said 0.75 years)." So at the distant station, Prime would observe Unprime to be aging just as fast as he was (but at a younger age?). What would he observe as he decelerates to the distant station? As he accelerates away from the distant station? As he decelerates at home? There would have to be some point at which Prime observes Unprime leaping ahead in years to catch up to and surpass Prime in age. At what point is that?

It occurred to me the other day that Einstein's special theory of relativity should never have been accepted unless he supplied the general theory with it. The special theory, on its own, leads to the twin paradox. You need GR to resolve this. But SR was proposed in 1905. GR was proposed and proven in 1920 - 15 years later. I don't know my history that well, so maybe the answer is that SR wasn't accept until GR was proven... or maybe scientific theories are accepted regardless of whether they make sense or not so long as they pass experimental testing... or maybe physicists were desperate for something to solve the paradoxes of light that the Michelson-Morley experiment made evident. Please enlighten me.

Thanks for the help, swansont.