Several centuries ago, the Pope decreed that all the Jews had to convert or leave Italy. There was a huge outcry from the Jewish community, so the Pope offered a deal. He would have a religious debate with the leader of the Jewish community. If the Jews won, they could stay in Italy, if the Pope won, they would have to convert or leave.
The Jewish people met and picked an aged but wise Rabbi Moishe to represent them in the debate. However, as Moishe spoke no Italian and the Pope spoke no Yiddish, they all agreed that it would be a silent debate.
On the chosen day, the Pope and Rabbi Moishe sat opposite each other for a full minute before the Pope raised his hand and showed three fingers.
Rabbi Moishe looked back and raised one finger.
Next, the Pope waved his finger around his head. Rabbi Moishe pointed to the ground where he sat.
The Pope then brought out a communion wafer and a chalice of wine. Rabbi Moishe pulled out an apple.
With that, the Pope stood up and declared that he was beaten, that Rabbi Moishe was too clever, and that the Jews could stay.
Later, the Cardinals met with the Pope, asking what had happened. The Pope said,
I think I have spotted a problem here. Jill does in fact observe the flashes simultaneously, but due to the finite and constant velocity of light, she concludes that the lightning flashes didn't occur at the same time, while Jack concludes that they do.
What Jack sees is this:
The flashes occur at the top of the panel, the yellow light rays travel towards Jack. Jack knows the locations of the lightning flashes, indicated by the red lines. Noting the flashes, and considering the constant velocity of light, Jack concludes that the lightning flashes occurred simultaneously.
Jill sees this:
Jill knows that the train is moving to the right with respect to the lightning flashes, so in this case the red lines are slightly skewed. Again, using the velocity of light, Jill traces back the times at which the lightning flashes occurred and notes that they were produced at different times.
I also found the following video quite instructive:
the only way that you can say that Jack is actually stationary, is that he is stationary with respect to the lightning flashes. You could do the same thought experiment with the head and tail lights of the train flashing on (so that Jill is stationary with respect to the events), and have a similar disagreement over the simultaneousness of the flashes, with the roles reversed between Jack and Jill.
I'll be interested to hear it. But let's give David his due...
I don't think Einstein is saying here that the embankment is actually stationary, and the train is actually speeding. If you include the preceding sentence:
the meaning of "in reality" changes a bit; he goes from a hypothetical ("If an observer sitting in the position M’ in the train did not possess this velocity...") to the case he was originally considering (i.e. with a moving observer). Furthermore, since this article seems to be focusing on simultaneity, and not so much on the relativity of motion, I don't think it's quite proper to draw conclusions from it regarding the latter.
In the case of presentism vs eternalism, I think it's interesting to note that both general relativity and quantum field theory (in the path integral formalism) treat the time dimension from an eternalist point of view, and at least in this aspect do not contradict each other. It absolutely possible, of course, that some future theory that combines the two may make reference to an absolute time frame; this still makes eternalism the most compelling choice (in the view of physical evidence) for the time being. And even if true, it does not disqualify the eternalist point of view.
As for general relativity, quantum mechanics and all other theories of physics being false: I agree, but with one reservation. To quote Isaac Asimov in The Relativity of Wrong:
I think it's not unreasonable to base metaphysical arguments on physical theories. At worst, it locks metaphysics in step with physics, forever progressing to an end they may never reach; one hopes that the view on the way is worthwhile. Besides, should metaphysical claims about reality be made without any reference to physical sciences? That seems like unnecessarily handicapping oneself.
I guess my point of view is best illustrated by the maxim of a former colleague: "At least it's not stupidly wrong."
They do need the extra space to fit together, of course, but my question remains: In both figures, the colored shapes form a 13x5 triangle; the triangles are equal, the shapes into which they are divided are equal, so why is there space for an extra square in the lower one?
(Keep in mind that I'm trying to trick you here, and that the answer resides in the lie I'm trying to feed you)
Indeed, parsec (cool username, by the way). The trick to the punchline is to make us believe that the guests paid $27 to the hotel and $2 to the bellhop, and asks why that does not add up to $30; in fact, they paid $25 to the hotel, $2 to the bellhop, and kept $3 to themselves, which does add up.
In a similar vein (and perhaps you have seen this one), why is the lower of these two triangles missing a square in its area, while it's made up of the same shapes as the upper one?
Yes, and the $30 is divided as follows: $25 to the hotel, $2 to the bellhop, and the guests keep the remaining $3. There is no need for the amount of money spent by the guests plus the amount kept by the bellhop to be equal to $30. Why should there?
That one is a bit silly; there's no need to arrive at $30 in the last step. Compare:
The hotel initially received $30. They kept $25, the bellhop kept $2 and gave $3 to the three men. Since 25+2+3=30, there's no problem.
From the point of view of the three men, they each paid $9 for a total of $27. Of this, $25 went to the hotel, and $2 was kept by the bellhop. Again, since 25+2=27, there's no problem.
The story is deliberately confusing in the last step, since it suggests that, for some reason, it makes sense to add the money kept by the bellhop to the money spent by the guests; and furthermore, that this sum should be equal to the money they initially paid at the counter. Both of these are false.
The same can be said about electrons, photons and other subatomic particles. Do you have similar objections to their supposed existence? If not, why not?
On the contrary: dark matter (to take an example) was introduced exactly because the earlier models on galactic dynamics failed to predict the observed stellar kinematics. You are right that there is little evidence for the existence of dark matter, but as assumptions go, it's not a bad one ("there is matter out there that our equipment can't detect" is really quite modest). The theory that comes closest to an alternative is Modified Newtonian Dynamics (MOND), which has its own problems and is similarly without evidence.
I can only recommend to work in science for a while; you'll soon realise that scientists are just like everybody else
Since I'm not a biologist I can't say I'm equipped to give you a good answer here, but I'll give it a shot.
It's true that planets other than the earth have conditions that would kill an unprotected human within minutes. It is entirely plausible, however, that other life forms can exist under those circumstances. Even on earth there are examples of microorganisms that thrive in extreme conditions, it wouldn't be a stretch of the imagination to suppose that similar life forms can exist in the methane lakes of Titan, or perhaps under the surface of Europa.
Of course you're right for saying that physics dictate what conditions give life. After all, biological organisms still follow the laws of physics. But in the case of extraterrestrial life, you seriously have to wonder what your definition of "life" is, and whether a structure you observe fits the definition or not. It is to be expected that life, if it occurs on other planets, will have originated and evolved in a very different environment form earth, and will probably be very different as a result.
I got my name from The Science of Discworld by Terry Pratchett, Ian Stewart and Jack Cohen. The authors argue that Homo Sapiens, Wise Man, is a rather arrogant name we call ourselves, and that Pan Narrans, Storytelling Ape, is a lot closer to the truth.
Hello Pgalaxy. Thanks for the question, I feel at home already! I assume your question pertains to water in a vacuum, not in the atmosphere of a planet (or a spaceship for that matter). If that's the case...
The naive answer is 0 K, since the vapor pressure of water in outer space is practically zero.
The easy answer is that water has no boiling point in outer space, since it can only exist in solid and gaseous forms under those conditions.
The complicated answer is: depends. If you were to bring a volume of water to outer space, it would start to boil, releasing water vapor in the vacuum of space. This causes the remaining water to cool down to the point where it freezes and forms a lump of ice. The temperature of the last remnant of liquid water just before it freezes or evaporates is the triple point temperature of water, 273.16 K (accidentally, this is how the Kelvin unit is defined). The fate of the lump of ice then depends on the temperature it has due to the radiative equilibrium with its surroundings: if it is heated up to its sublimation temperature of about 100 K, it gradually vaporises; if it stays colder than that temperature, it can hold out more or less indefinitely.
I hope this answers your question.
Lewis: I got my Ph.D. is astrophysics two years ago. Right now I'm working on boundary conditions in meteorological models. I still consider myself an astrophysicist, though.