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Showing content with the highest reputation on 01/02/18 in all areas

  1. 2 points
    Also, ribozymes are clearly not the ancestor of eurkayotic life but fall into the category of the RNA world hypothesis, which is far from an established fact. More specifically though, how do you define "only once"? There are obviously plenty of ribozymes and their early origins are still unclear. Also chromosome re-arrangement has been observed in many species and is clearly not an unique event either. Forgot to add, endosymbiotic events related to formation of eukaryotes also happened more than once. Mitochondria likely originated from aerobic bacteria, whereas plastids likely evolved from cyanobacteria.
  2. 1 point
    I'm going to try an analogy here to try and get the idea across. Imagine you have two men. They start at the same spot and start walking in different directions. After they both have walked an equal distance, on man turns so that his new path will cross the other man's path. After both have walked an equal distance again, they come to a stop and measure how far they are from where they started. The man who changed direction during his walk will find himself on the other man's path line, but closer to where he started than the the man who didn't change direction. Now it doesn't matter how they measured the distance they walked, they could have used a tape measure (equivalent of measuring time with a clock) or counted the number of steps they took of equal stride length (equivalent of biological aging or personal perception of time passage), They still end up with one man closer to where they started than the other. The same is true for accumulated time difference due to Relativity. It doesn't matter how you measure "time", by a clock or human "age", less time will have passed for one person than for the other. You simply cannot separate "aging" from time measured by a clock. They are both the result, on a fundamental basis, of the same thing.
  3. 1 point
    I worked on PU foam R&D for 8 years so I know a bit about it. Isocyanate is highly reactive and is all consumed in the manufacturing process. Such foams are widely used in cot mattresses and institutional bedding. The combination of mattress cover and condition is highly significent in safety terms. I wouldn't buy a secondhand one in any case. Modern formulations are safe although there have been questions related to cot death and I would not advise using a secondhand one for babies, especially very young ones. There was also govt. advice to lie babies on their backs. Again, I wouldn't buy a secondhand one. There were also concerns about the extreme flammability of early formulations and much development focussed on dealing with this problem and you would be advised to check flammability ratings on any products you have. Latex foams do not suffer from the same potential disadvantages but again should be checked via manufacturers advice.
  4. 1 point
    To directly compare the times between the accelerated and non-accelerated clock, they have to start next to each other and end up next to each other. The accelerated clock has to accelerate away, then reverse the direction of its acceleration and return to the other clock. So first we will examine the instant the clock starts its acceleration. At this moment it is still co-located with the other clock and has zero motion. What will be the observed time dilation between the two clocks? Zero. At that instant, even though the one clock is accelerating, both clocks clocks will determine that they are running at the same rate. As the accelerating clock gains velocity with respect to the other clock, you now have to consider what each clock separately would measure. For the non-accelerated clock, the accelerated clock would exhibit time-dilation and run slow. That time dilation would however just be due to the relative velocity difference between the two clocks, the acceleration rate of the accelerating clock adds no additional effect. This remains true for the entire trip. The end difference in the elapsed times of the clocks when they meet will be due to the accumulated effect of the this time dilation. For the accelerated clock, the acceleration does matter in terms of what it would measure as happening to the other clock. But not just the magnitude of the acceleration, but its direction and the distance between the two clocks. There will also be the normal time dilation factor due to relative velocity between the clocks. As the two clocks separate, the relative speed increases, as does the distance. The increase in speed causes it to measure the other clock as running slower. The increasing distance along with the direction of the acceleration adds an additional slowing to the other clock. The greater the separation, the greater this effect becomes. Now the accelerating clock reverses its direction of acceleration, to first come to rest with respect to the other clock, and then start the trip back. Once the direction of the acceleration vector goes from away to towards the other clock, the time dilation factor due to the acceleration reverses, and causes the other clock to appear to run fast. This will be counteracted by the time dilation factor due to the relative motion. As the clock continues to slow relative to the other clock, the relative motion time dilation factor decreases and the speeding up of the other clock due to the acceleration factor dominates more and more. Eventually the relative speeds reaches zero and the accelerating clock starts speeding up again, but now back towards the other clock. The distance starts to decrease, lessening the factor that speeds up the other clock and the relative speed increases, increasing the slowing down effect. When the two clocks meet up again, the total elapsed time difference will be due to the accumulation of the all the factors given above, and the clock will find that less time has accumulated for it than has for the other clock. Both clocks come to the same conclusion as to the total elapsed time difference between them, but contribute this difference to different reasons and different time dilation effects. While the total accumulated time difference between the clocks is absolute, the time dilation between them never is. Do not confuse "time dilation" which is the relative tick rate as measured between two frames at any given moment with "total time accumulation difference". For the non-accelerating clock the time dilation measured for the accelerating clock always has it running slow except for those brief moments when the clock are at rest with respect to each other. For the accelerating clock, the time dilation factors combine so that for part of the time the non-accelerating clock runs slow and for part of the time it runs fast. Which is the "real" reason the clocks differ at the end? Both. Neither clock's view of what happened during the trip has precedence over the other. they are both equally true. I realize that for many, this is a hard pill to swallow. They want a singular "cause" that they can point to that results in the time difference. Unfortunately, the universe is not obliging in this manner. As to the muon experiment. The fact that the muon is in free-fall is not a factor. It is not the gravity or acceleration "felt" by the muon that counts with gravitational time dilation, it is the difference in gravitational potential. Specifically, what this means in the case of the muon is that it is related to the difference in the altitude between the ground clock and the muon. If you were to take two clocks and suspend them from the same altitude, and then let one start to drop. In the instant you released the one clock it would go from not being in free fall to being in free fall, but this would not cause any change in its tick rate as compared to the other clock. That wouldn't start to occur until the clock actually changed altitude and relative velocity with respect to the other clock. That beside gravitational time dilation as far as the muon experiment is concerned is just too small to produce the measured results. It is the relative velocity between muon and ground clock that produces this. Like in the accelerated clock example above, the reason behind the muon surviving until the reaches the ground depends upon whether you are in the ground rest frame or the muon rest frame. In the ground rest frame, the muon undergoes time dilation, ages more slowly and thus lives long enough to reach the ground from the altitude where it was created. In the Muon frame, the Earth and its atmosphere is length contracted, thus the distance between the point of the atmosphere where it finds itself upon creation and the ground is short enough for it traverse during its normal life-time. And while the ground clock undergoes time dilation and runs slow according to the Muon, due to the relativity of simultaneity, the ground clock, according to the muon, reads a later time at the moment of the muon creation, than the ground clock frame would read on the ground clock upon Muon creation. For example, if the muon-ground relative velocity is 0.999c, and the muon is created at an altitude of 10km and when the ground clock reads 0 as measured in the ground frame, Then the ground clock will read ~3.34 e-5 sec when the Muon reaches it. In the Muon frame, the Muon will be 447 meters from the ground upon creation, and will reach the ground clock in ~4.77e-7 sec, during which time, the ground clock will tick off ~7e-9 sec, but the ground clock would have read 3.33393e-5 secs when the muon was created, and this plus 7e-9 sec equals 3.34e-5 seconds, so both the muon and ground clock agree on the ground clocks reading when the muon arrives. (though they don't agree as what the ground clock read upon the muon's creation). So again, we have two frames agreeing on the end result, but not agreeing upon how that result was arrived at.
  5. 1 point
    I'm not sure vertical ethanol farming would manage 3 acres per floor. Maximising the area exposed to sunlight would mean limiting the area to that which allows sunlight to penetrate. Where vertical farming makes effective use of sunlight it makes equivalent large areas that are shadowed; you can't pack them too closely or they shade each other. Light will penetrate mostly from the sides rather than above; no light coming from above will reach the floor below the top one. Ultimately no more sunlight is available than with horizontal farming. Replacing sunlight with artificial lighting would introduce a major energy input in a process intended to maximise energy output - and even if the lighting is high efficiency, plant conversion of light to energy is not - more than 2% of the sunlight converted is considered very good. That may be improvable by selection, breeding and genetic engineering - but enough? Artificial lighting is not so good; it has to use sunlight as it's principle energy source to deliver more energy than it consumes. The innate usefulness of biofuels has been based on the fact that ones like wood just grow, often on agriculturally marginal land, without cultivation and with minimal processing. I suspect the much higher efficiency of Photovoltaics combined with electrically driven chemistry has greater potential to produce transportable liquid (or gas) fuels. How well they can compete with (still improving) batteries will probably be revealed over the next decade or two.
  6. 1 point
    Yes you are. And, as usual when you make stuff up, you are wrong. But that doesn't include mass. https://en.m.wikipedia.org/wiki/Information_theory
  7. -1 points
    OK, finally I can reply again (I was stymied by being a first day member there for a while). So a clock slows when it moves fast, that's been proven evidently. But I don't see how the behavior of a clock necessarily relates to aging. So StringJunky, a clock goes through time the same as an aging person or an opening flower and because the clock shows a different process at fast speeds then the assumption is that a person aging, or a flower opening, would experience changes in their processes that would coordinate with the changes in the clock? I don't get how you make that jump? Where's the logical leap from rate of clock change to rate of aging or rate of flower opening? Can we not age, or can flowers not bloom, independent of the clock rate? Outrider you told me "Time is what clocks measure. A clock can be anything that has a rate of change, so an aging person can be a clock." I don't get that. An aging person, scientifically speaking, is different from a clock. A clock is a fairly precise measuring device, the aging person is not. As I said above, why does the behavior of the clock at high speeds tell you anything about how a person ages relative to that clock's changes at high speed? That's the part that makes little, or no, sense to me. Plainly, I don't get why people have conjured that aging happens by clock rate. People age by time, not clock rate. So, just because a clock rate changes at speed, I don't see how that has to do with time in regards to aging or blooming.
  8. -1 points
    Obviously. But you knew that was an "egging on" question, right? Time is personal, not mechanical. Agreed. The mechanism of time is an invention, not a given part of the universe. Time was never given to us, we created it.
  9. -1 points
    Thank you. That means a lot to me actually that I'm not completely crazy! But I guess physics is kinda wrong when they try and describe time in regards to age.
  10. -1 points
    The important point here is that time dilation is not an effect on the clock. It can't be. For example, right now you are traveling at 0 km/h relative to your chair (no time dilation) you are also travelling at hundreds of miles per hour relative to Mars (a bit of time dilation) you are also travelling at 99% of the speed of light relative to cosmic rays (a lot of time dilation). Your clock can't be running at multiple different speeds, affected by every relative velocity. OK, that's all fine, but does it have to do with human age?