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Showing content with the highest reputation since 03/14/18 in all areas

  1. 4 points
    Stephen Hawking has passed away at the age of 76 on Pi day, 3/14/2018. http://www.bbc.com/news/uk-43396008 https://www.theguardian.com/science/2018/mar/14/stephen-hawking-professor-dies-aged-76?CMP=fb_us
  2. 3 points
    Yes, you must distinguish between truth1 and truth2... Just kidding. To be honest, I do not like the substantive 'truth', even less when written as 'Truth'. I think the first thing is to look on which 'objects' the adjective 'true' applies: these are propositions, or complete systems of propositions, where I think about e.g. scientific theories. What it means is that they fit to what they describe. If they do not, they are false. (Or they are meaningless ('colourless green ideas sleep furiously'), or they do not describe a situation unambiguously ('One cannot see light' )) So simply said, one can define 'truth' as the correspondence between a description and reality. So it characterises a relationship between propositions and facts. Which e.g. means the 'Truth' is not out there. We find out if a proposition is true, if we find out that the description corresponds to reality. It is an attribute of propositions ('in there') and reality ('out there'.) I think this meaning of 'true' is simple. But that does not mean that it is easy to find out which propositions (or theories) are true. The two topics should not be confused: what 'true' means on side, and how we find out on the other. I think that some of the examples given are wrong: e.g that about simultaneity in relativity. Are two events simultaneous or not? Well, we know exactly how this depends on from which inertial frame you are observing these events. So we have to amend it to 'for observer A the events are simultaneous, for observer B they are not'. If we know how the perspective has influence on what people observe, then we know that there is nothing to quarrel about. It is as if two people are facing each other, and quarrel about the question if the chair stands at the right or at the left. If you take the perspective in account, the whole problem has vanished. Same with what is true today is false tomorrow. If it was an 'eternal truth' (something like F = mv, like Aristotle thought), and today we know it is false, then it was false all the time. We erroneously took it for true. But truth hasn't changed, because reality did not change. Same with the opposite: reality changes. It is drizzling. It is really true! I see it when I look out of the window! But of course this event is local: where I live, and am now, it is drizzling. It makes no sense to quarrel about the truth of 'it is drizzling', if I do not take the context in account. When I am going somewhere else tomorrow, then it is still true that 'in Switzerland at 17.03.2018 16:30 local time, it is drizzling'. Even if it is beautiful weather at the place where I am tomorrow. Personally, I would prefer to separate some concept pairs: For factual knowledge, 'true' or 'false' apply, because there can be a kind of correspondence between factual propositions and reality For morality, I would use 'right' or 'wrong'. There is no way that science can find out what is morally right or wrong. It can help if facts play a role in a moral decision ('if you do this some people might be killed, if you do that, the risk is negligible'). But this already presupposes that both agree on the norm that killing people is wrong. For aesthetics it becomes more difficult: beauty, interesting, fascinating or ugly, boring, ...The difference with morality is that it has a very strong personal factor. The compulsion to come to an agreement is less than in morality, but do not underestimate the intersubjective character of these aesthetical norms. If these is a discussion on how to renovate the old city centre, it can become very important that people agree. Well, then they are wrong. Truth is not subjective. Beauty has a strong subjective side, morality less, but truth is definitely not subjective.
  3. 3 points
    I think Gees introduced the topic of an elephant. Koty is the blind man holding the trunk, and trying to describe it. Strange is the blind man holding the ears and trying to describe it. Ten oz is the blind man holding a leg and trying to describe it. And Dimreepr is the blind man holding the tail and trying to describe it. Sorry Gees, but you've created a mess. I think you're gonna have to re-state and clarify the OP.
  4. 3 points
    The simple answer is that the universe works in such a way as to prevent your ever exceeding c relative to your starting point. You are essentially asking what prevents you from constantly accelerating at 1 m/s2 until you exceed the speed of light. If the Universe operated under the Rules of Newtonian physics, nothing. After 7 years, 21 days, 20 hrs, 47 min and 38 sec, you would be moving faster than light. However, we don't live in a universe that follows Newtonian rules, but follows Relativistic ones instead. And one of those differences in rules is in how velocities add together. Under Newton if you want to get the sum of two velocities, you simply add them together like this, w=u+v. Thus if you were moving at 1 m/s relative to some reference and then added 1m/s to your current speed, you would be moving at 1+1=2m/s relative to the initial reference. However, it turns out that this isn't correct. the right way to add the velocities is by w= (u+v)/(1+uv/c2) where c = the speed of light in a vacuum or 299,792,458 m/s Now when you add 1 m/s to 1m/s you get a resultant velocity of 1.9999999999999999777469988789276 m/s almost, but not quite 2 m/s At low speeds, this doesn't amount to much, but as the speed increase, the difference starts to mount up. If you were moving at 0.1c and increased your velocity by 0.1c, you would be moving at .198019802 c relative to the point you were initial moving at 0.1c relative to. If you boost you speed by another 0.1c, you will now be moving at .2922330097c relative to the initial frame. Do this 7 more times, and instead of moving at c relative to the initial frame like you would under Newton, you would be moving at 0.7629989373 c. Each time you add change your speed by 0.1 c relative to your current speed as measured by you, you add less than 0.1c total change in your velocity. And the closer you get to a total of c, the less change in total velocity you'll end up with, and no matter how you try and add up the velocities, the resultant velocity will always end up being less than c.
  5. 3 points
    It is a sad day, the world lost a great mind. His sense of humor was a great addition to his work - his singing of the Monty Python "Galaxy Song", the poker scene on Star Trek The Next Generation, his appearance on episodes of "Big Bang Theory" and the Simpsons...countless interviews and comedy shows he appeared in. He had a great life considering that he made it to 76 when he was getting 2 years max at 22 years of age. On top of his work in physics he left 3 children, a major hollywood film was made as his biography - who could ask for a more fulfilling life.
  6. 2 points
    "The opponent conceded in exchange for the antidote" (paraphrase from twitter) I fail to see why his win would be worthy of discussion, as it was a foregone conclusion.
  7. 2 points
  8. 2 points
    Yes indeed. Sorry about that. I did dispatch it, but it seemed to get sidetracked and last time I saw it some idiot had sent it out towards Mars.
  9. 2 points
    My friend and I were playing in the field. We found some stones and began stacking them. We’d go home to our family, have dinner, then for some reason we’d come back to the field the next day and the day after that and keep stacking stones. Soon, as we continued stacking them, they became taller and taller then still taller some more and a wall began to form. Others from the village soon noticed and before we knew it they began stacking stones of their own right beside us. The wall grew and changed and evolved, but had a history and told a story of our community; of our shared experience. It became an organic expression of time and effort and people would always learn new things about the universe and about themselves when gazing upon it. Then one day my friend realized that sometimes others around us were better at stacking stones than he was. He saw that, even though many of his stones were perfectly fine, some were clearly mistakes. He was embarrassed, especially when his work was compared to that of others who’d been practicing stone placement for a very long time; much longer than he and me. My friend then asked all of us in the community to remove his stones, to pull them from the wall. He kept advocating for us to rip out his stones and pretend they never existed, but we could not. If his stones were removed, all of the others placed on top of them would become unstable. If his stones were removed, the whole wall would crumble and fall and nobody wanted that, not even him. So, my friend had to live with it. He had to recognize that, even though his stones weren’t placed perfectly, they were critical to the structure of the wall itself. It could not exist in its truest form without them. Removing them would ruin the work of everyone else and my friend had to use it as an opportunity to learn from his errors and become a better version of himself. Your posts are part of our wall. Like a tapestry or quilt, it would never be the same without them. We’re sorry you want them removed, but we’re also thankful you shared them with us and appreciate what you’ve contributed, but we can’t pull that thread or remove those stones no matter how many times you ask. We’re a part of the wall too, and that just wouldn’t be fair.
  10. 2 points
    I think these two quotes sum it up for me: the reality of the elephant is absolute, impersonal and objective; the perception of the elephant is relative, personal and subjective. I'm reminded of a brilliant 80's Irish sitcom ( Father Ted ) where Ted was explaining to dumb Dougal that cows are normally the same size but the very small cows were " far away ". Regarding the OP, my perception was that Gees , in this case, was using truth to mean honesty, when asking if truth can be trusted, so i would say that absolute, objective Truth/Reality can be trusted, ( if we can recognize It as such ), whereas relative, subjective truth obviously can't be completely trusted. That seems pure and simple but, as Oscar Wilde said: " The truth is rarely pure and never simple ". As for sticking to unwavering, absolute honesty, i would say that a benign expediency, or even silence, is sometimes the better course to follow. Are right and wrong related? I would say no - if something is right, it's just right; it isn't right because something else is wrong: 2 + 2 = 4 isn't right because 2 + 2 = 86* is wrong. ( * That is wrong, right ? ). .
  11. 2 points
    The fidelity of our description of the universe improves with experience but we can never know it absolutely because we and it are constantly evolving.
  12. 2 points
    As far as I know, it only exists in spy fiction.
  13. 2 points
    Take the energy content and divide by c^2 Batteries tell you how long they will run, and at what current, e.g. 1 amp-hour. You also have a voltage. E = Pt = IVT So 1 amp-hour at 1 V would be 3600 Joules. The mass difference would be 4 x 10^-14 kg
  14. 2 points
    From Light Into Heat. His Radiation Remains. The Journey Complete. ..
  15. 1 point
    Real engineering is quite good.
  16. 1 point
    A month or so ago, I was asked to provide a logical explanation to the Twin Paradox that showed why symetrical views of time was not a paradox or how was symmetrical views of time completely consistent with the time deviation experienced between the twins. So as promised I fully explain: Why length contraction is the reason why the twins experience time deviation. Why time deviation was not a paradox with the twins symmetrical views of time because length contraction is the asymetrical component that was never considered. Finally, I show how their symetrical views of time really are completely consistent for the entire journey using a trasponder solution with each other. As always, I will be using the example given in Wikipedia so that you can verify the results with those given in that example and I can skip the math for simplicity sake. I will only be providing the logical models that fully explains the paradox. BTW, this is a good example of my previous statements that while logic may be prone to intuitive errors of false premise, such as the Earth is the center of the Universe because everything appears to revolve around the Earth, math is just as prone to intuitive errors of false conclusions. The key points of the problem are: The ship carrying one of the twins goes straight to Alpha Centauri and back. Acceleration is assumed to be an insignificant factor so velocity is a constant 80% of the speed of light in both directions. Alpha Centauri is assumed to be in relativisticly static motion relative to the Earth with a proper distance of 4 light years. Each twin is equiped with a powerful transponder that pings with a source frequency of exactly once per second or 1Hz. The Earth twin sees that Alpha Centauri is a static 4 lightyears away. Therefore, he calculates the trip will take 4/0.8 = 5 years each way or 10 years total. The ships twin has a different perspective of the trip when moving at 0.8c due to length contraction, the distance is only 60% of the proper distance or 2.4 light years away. Therefore from his point of view, the trip will only last 3 light years each way or 6 years total. So when he returns, he experiences 6 years while the Earth Twin experiences 10 years, however that is not the paradox. The paradox is based on the fact that each twin should have symmetrical points of view of their brothers time which is true: When the ships twin is on the outbound leg moving away from Earth at 0.8c then each twin sees their brothers time as moving at 1/3 of normal, or they would each be receiving a transponder ping only once every 3 seconds. When the ships twin is on the return leg, then each twin sees their brothers time as moving at 3x normal or they would each be recieving 3 pings/sec. These time shifts are due to the relativistic redshift which I didnt bother working out the math again, but the formulas are pretty simple and include time dialaion plus normal doppler effect due to lagtime, so that you can verify the results yourself or just refer to the Wikipedia example which uses the exact same problem. The logical resolution to this paradox is the fact that while their views of each others time is symetrical, their views of the distance traveled is asymetrical. The reason why is that the Earth, Alpha Centari, and the space in between the two are all in the Earths inertial reference frame, while the ship plus what is inside the ship is all that is in the ship’s inertial reference frame. The Earth twin sees the ship is length contracted by 60% which has no bearing on the trip The ships twin sees the Earth’s inertial frame as length contracted and as we said, the Earth, AC and the distance inbetween is all included within that inertial reference frame. Therefore, from the ship’s twin’s point of view the distance is length contracted by 60% of 4 light years or 2.4 light years. So with 60% less distance to trave, then the trip takes 60% less time to travel from the ship twins point of view. Another words while their point of view of time is symmetrical, their point of view of distance is asymtrical which accounts for their deviation in time experienced. We can confirm this by correlating their point of view with lagtime. Another words, from the Earth twins point of view, the ships twin would take 5 years plus it would take 4 years for the light (or transponder signal) to get back to Earth from Alpha Centauri: 5 years + 4 years = 9 years That means the Earth twin would expect to witness the ship actually execute the turnaround 9 years after the ships departure. Or when the transponder signal recieved back on Earth would change from 1 ping every 3 seconds to 3 pings/second then the ship would have executed the turn which would happen 9 years after the origional launch. If you do the math and count the pings received during those 9 years at 1 ping/3 seconds adds up to: 9 years x 1/3 = 3 years which is actually what the ships clock would read at the turn around by both twins. Events that include both a time and a place must always be consistent to any inertial frame. On the trip back to Earth, the journey would only seem to take 1 year as perceived by the Earth twin so: 9 years + 1 year = 10 years total time as expected by the Earth twin. However, during that 1 year, the transponder is pinging 3 times per second so it adds up to 3 years 1 year x 3 = 3 years 3 years + 3 years = 6 years total. The Ships twin experiences something different. He hears the transponder received from Earth ping once every three seconds, and since the outbound leng only takes 3 years, he sees the Earth clock as counting only 1 year. 3/3 = 1 year On the return leg, the ship’s twin experiences three years worth of pings that are pinging at 3 pings per seconds, therefore the Earth clock advances 9 years during his 3 year return leg. 3 years x 3 = 9 years 1 year + 9 years = 10 years which is the time elapsed back on Earth. So not only is the math consistent, it sould not even be a surprise to either twin that their brother has aged differently.
  17. 1 point
    Actually, if in a region the gravitational potential is constant, there is indeed no force. Force is the (negative of) derivative/gradient of potential.
  18. 1 point
    - What is matter? - Never mind. - What is mind? - No matter.
  19. 1 point
    Cognitive dissonance (the force) is strong with you, but which side will you choose? The gun or Jesus (light or dark)?
  20. 1 point
    Read your Bible (hint Joshua)
  21. 1 point
    That the word "panic" comes from the ancient Greek god Pan. From Wiki Etymology The word derives from antiquity and is a tribute to the ancient god, Pan. One of the many gods in the mythology of ancient Greece: Pan was the god of shepherds and of woods and pastures. The Greeks believed that he often wandered peacefully through the woods, playing a pipe, but when accidentally awakened from his noontime nap he could give a great shout that would cause flocks to stampede. From this aspect of Pan's nature Greek authors derived the word panikon, “sudden fear,” the ultimate source of the English word: "panic".[1] ------------------------------------------------------- Effects Prehistoric humans used mass panic as a technique when hunting animals, especially ruminants. Herds reacting to unusually strong sounds or unfamiliar visual effects were directed towards cliffs, where they eventually jumped to their deaths when cornered. Humans are also vulnerable to panic and it is often considered infectious, in the sense one person's panic may easily spread to other people nearby and soon the entire group acts irrationally, (...) ---------------------------------------------------- So for the ancient Greeks, when someone got under panic, it was caused by the intermission of the god Pan. At the end of the Marathon battle, the myth says that runner Pheidippides encountered the god Pan who asked him why the Athenians didn't adore him. Pan had come to the battlefield and helped the Athenians to win the battle. Pheidippides answered that from now on, Pan would be adored by the Athenians (and indeed since then they create a temple to Pan in a grotto under the Acropolis. The concept that Pan helped the Athenians makes me think that when they saw the Persians run back to their ships it was for the Athenians a sign of panic.
  22. 1 point
    If we get back to the original problem, space-time is regarded as 4 dimensional since position can be specified by 4 independent coordinates. In GR, the some region around any point in space-time looks like a R4 - e.g. for any point near a black hole you can still find a region (possibly very small) that looks like R4. I think we have been sidetracked from the original question by the language used, which tried to simplify the answer by saying that the coordinates can be used to find an object of some sort. Actually the coordinates specify a location even if there is nothing there, or we do not know where something is. Methods of finding things is a totally different topic about which discussion could go on forever.
  23. 1 point
    FWIW, I think Phi was referring EXACTLY to DJT
  24. 1 point
    I see. Thank you. I think I prefer my misinterpretation.
  25. 1 point
    There's a flip side to that; jokes that only make sense in a language other than that in which they are written. Un petit d'un petit S'étonne aux Halles Un petit d'un petit Ah! degrés te fallent Indolent qui ne sort cesse Indolent qui ne se mène Qu'importe un petit Tout gai de Reguennes. Which looks like (fairly bad) French poetry meaning something like A child of a child Is surprised at the Market A child of a child Oh, degrees you needed! Lazy is he who never goes out Lazy is he who is not led Who cares about a little one All happy with Reguennes but which is remarkably funny when a natural speaker of French reads it to an English audience who instantly recognise it as this nursery rhyme Humpty Dumpty Sat on a wall. Humpty Dumpty Had a great fall. All the king's horses And all the king's men Couldn't put Humpty Together again. (I have pinched most of that from the wiki page) https://en.wikipedia.org/wiki/Mots_d'Heures
  26. 1 point
    Time is an element of the continuum called spacetime. Trying to cut the continuum in parts lead to errors. IOW there is no Time by itself, and there is no Space by itself.
  27. 1 point
    OK. So the light we see now is not from the same place where the matter around us came from. As you say, that light is long gone. However, we now see the light that is reaching us from further away. Take the CMB for example, the radiation we are receiving now is coming from about 40 billion light years away. To understand why we are still receiving light from the Big Bang after all this time, maybe the "surface of last screaming" analogy will help: https://ned.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver7_2.html (If you need to relate that more closely to your question, imagine all the people slowly walking away from you. It doesn't really make any difference.)
  28. 1 point
    There are things that are axiomatic, 2+2=4, but what is the value of 4, a square has 4 equal sides, but how big is it? Perception and truth aren't the same but they are interdependent.
  29. 1 point
    Koti; +1 Because you have obviously spent some time considering truth as is evidenced by many of your posts in this thread. Yes. In my threads regarding consciousness, I have learned that people can only deal with so much truth, so it is often necessary to give them little pieces and let them stew on those ideas for a while. I am reminded of the movie, A Few Good Men, where Jack Nicholson states, "You can't handle the truth." (chuckle) A few years back, in another forum, I wrote a thread entitled, A Measure of Truth. In that thread I tried to establish rules that would help me to define and understand what is true and what is not true and how I would determine and measure truth in order to create more valid premises. In this thread, I had noticed that many people seem to confuse right and wrong with truth, so I wanted to explore that idea. What I have learned is that there are social truths, political truths, emotional truths, and others that I had not previously considered. These truths are often related to right and wrong, so they can be confused with right and wrong; this thread has already given me much information and much to think about. Well, knowledge is subjective and truth is knowledge. If you remove all of the people and all of the conscious life, can there be knowledge? Can there be truth? How could you possibly know or prove it? You can only know something if there is someone to know it. That makes it subjective because knowledge and truth both require a subject. I don't agree that truth is unreliable, but will acknowledge that it can be elusive. This is why we need philosophers and scientists to help us find it. Truth is measured. This is why we can say that something is more true than not, or more or less true, or somewhat true. I don't remember anyone ever telling me that something is somewhat a fact; it either is or isn't a fact, so I think we can find a decent consensus in some things. Gee Strange; +1 For understanding that truth is complex, and I think I owe you a point anyway. In the thread, Science is a Subfield of Philosophy, Itoero made it very clear that truth was subjective and therefore unreliable and unprovable. I think that this recent example is what brought it to my mind, but I have heard similar arguments before. Truth is relative, so it also relates to time. What was true a moment ago may not be true now; what is true now may not be true in a moment. This makes some truth as changeable as the wind -- which may be blowing now, but not in an hour. Regarding right and wrong, I am reminded of an old movie that I saw many years ago about Jim Thorpe. (I think I have that name right -- Burt Lancaster played the part of Thorpe) Anyway, he was an American Indian, who won a lot of medals in the Olympics and then had them taken away from him. In the story, he was in a "white man's school" with another boy and they were discussing their history books. One boy said, "Why is it that when the white man wins, it is a great victory, but when the red man wins, it is a terrible massacre?" He had a point. For that matter, what were they doing in a "white man's" school? Well, that is easy to understand. When the Europeans "discovered" the new land, they did not seem to notice that more than 300 tribes and nations of people had already "discovered" it. What the Europeans did notice was that the red man was different. Being linear thinkers, the Europeans realized that because of this difference, one group had to be wrong, and the Europeans did not intend to be wrong. That made the red man wrong by virtue of his existence. Putting the children in a "white man's" school was just another way of trying to make the red man more right. Which part of the above do you think is not arbitrary? Where is truth in this morass of right and wrong? The nature of truth is subjective and that makes it relative. It is relative to time, perspective, and circumstance, but more than that it is often measured and even balanced with other truths, so it is difficult to know. I think that when people do not trust truth it is because they do not know whether or not it is truth, or they don't recognize it. Gee Migl; +1 For making a good point. Digging around in a mess does not often solve much, but it can bring things to light. Although Koti, Strange, Ten oz, and Dimreepr are all blind in this scenario, they can still talk and type, so they can share their findings. Maybe we can learn something about the elephant by sharing our thoughts. That is what forums are for, aren't they? Maybe we should hurry this up before Dimreepr gets wet. Gee There are other posts that I would like to address, but this is St. Patty's day and I have Murphys, Heffernans, O'Gradys, and O'Briens in the family tree, so I will be busy for a while.
  30. 1 point
    Morals being written in the hearts of men (as according to Romans) and the knowledge of good and evil (aka morals) being the result of eating the forbidden fruit (according to Genesis). Unless you want to say after the fruit was eaten then knowledge of good and evil was written in the hearts of men - you can make up anything you want. But this whole line if discussion just highlights the point that there can be no sensible discussion when taking the bible literally.
  31. 1 point
    I doubt anyone will miss the fact that your position is that "every gun is an assault weapon capable of killing an entire classroom of children". If you can't recognize the difference between a field shotgun and a bump stock equipped AR15, there's no sensible discussion to be had. Just to confirm - your position is that the only effective form of gun control is a 100% ban on all firearms? You do know that the only country in the world with zero private gun ownership is North Korea, right? Everywhere else effective gun control includes civilians owning guns for recreational activities.
  32. 1 point
    2+2 = 4. Read that aloud. Now read this: "Marcus was wrong."
  33. 1 point
    That suggests you should (must) be able to uniquely determine whether every single statement is either true or false. If not, how do you know it is binary. What about things that are unknown? Or unknowable? Or partially true? Or provisionally true? Or conditionally true? If you look at Snopes and other fact-checking sites they don't have a binary distinction because they know reality is more nuanced than that. What about facts that are relative. Is it "true" that the Sun is stationary and we orbit around it? Or is it true that the Sun orbits the galaxy and we follow a complex path around that? All motion is relative so can you say that it is true that A is stationary and B is moving? Can you say it is true that two events happened at the same time when, from another frame of reference one could have happened before the other or vice versa?
  34. 1 point
  35. 1 point
    A documentary is a poor place to get info, possibly a documentary might prompt you to start looking, but I can probably find a documentary that asserts the moon is a hollow alien spaceship..
  36. 1 point
  37. 1 point
    More evidence that Trump has no idea what he's talking about much of the time. Most economists don't worry over trade deficits, and they aren't the problem Trump thinks they are. They only SEEM unfair to someone looking only at the surface, with no understanding of the depth of economic complexities. IOW, they're mostly cable news fodder to get listeners outraged over nothing. Trump will bring that same shallow lack of understanding to talks with NK, and he's also ensured that his State Dept will now openly be seen as an extension of the CIA (which I'm told by DC folks has always been a problem, but now the gloves are off). I don't see this ending well for the US. Trump and Kim have competing goals since both need to be seen as the stronger. I see Trump giving away too much and then lying about how great a deal he made, OR he shuts the talks down by being too hardline, OR he becomes "impressed" with Kim (there's going to be TANKS, ffs!) and how he's handled things in the face of so much adversity and we end up with Trump convincing half the country that Kim, like Putin, is a strong leader to be admired.
  38. 1 point
  39. 1 point
    There's a sizable bunch of clever people doing woodwork. Some luthiers, to name one group, can talk science with the best of them.
  40. 1 point
    Tip for anyone having the same issue: Save the picture to your hard drive and drag&drop it into a google graphics search. It works wonders
  41. 1 point
    No, it isn't. To put numbers to my earlier example: Acceleration due to gravity is GM/r2 Gravitational potential is -GM/r For the Earth, the difference in acceleration at the surface and 1 earth radius above the surface is 7.35 m/s2 The difference in potential is 31255879.6 joules/kg For our 4x Earth mass planet, the difference in acceleration between surface and the same altitude above the surface is 5.45 m/s2 The difference is potential is 41674506.2 joules/kg This is 33% larger than that for the same altitude difference for the Earth, while the difference in acceleration is only 74% as much. You can even have a difference in potential without any difference in acceleration. In a uniform gravity field, the difference in gravitational potential would be found by gh, where g is the acceleration due to gravity throughout the whole field and h is the height difference between them. In this case, there is no difference in acceleration over the region being measured (gravitational potential over small height differences approach this ideal, as g changes insignificantly over the region considered.)
  42. 1 point
    To build on what swansont has already alluded to. The fact that our Earth observer and space traveler experience the same local acceleration is not the determining factor in terms of the time dilation each would measure in other clocks. As swansont said, gravitational time dilation is due to the difference in gravitational potential, or in other words, the total effect of the gravitational field between the position of the two clocks. One way to visualize this is to consider how fast would something dropped from the higher altitude be moving when it reached the lower altitude. That would be a measure of the difference in gravitational potential. So if we take an object and drop it from a altitude 1 earth radius above the surface, when it starts its fall it will experience 1/4 the acceleration it does at the surface and it will hit the ground moving at some speed. A clock placed at this altitude will run faster than one on the surface. Now if we put a clock on the surface of the world with 4 times the mass of the Earth and twice the radius, it will experience 1g just like a clock on the surface of the Earth. If we put an object 1 earth radius above the surface, it will experience 4/9 the acceleration as the surface. If we drop an object from this height, it will hit the surface moving faster than one dropped from an equal height on the Earth. In addition, a clock placed here will run faster than one on the surface by a greater factor than the difference in rate between the two clocks separated by the same altitude in the Earth scenario, even though the difference in acceleration experienced by the Earth clocks is larger than the difference for the second set of clocks. When applying this to our accelerating space traveler, to use the equivalence principle, we have to consider what the equivalent gravitational field to his acceleration would be like. In this case, it would be a uniform gravity field that extends to infinity along the line of acceleration that does not diminish in strength with distance. Clocks that are in the direction he is accelerating will run fast, and clocks in the opposite direction will run slow. The greater the distance between them and these clocks, the larger the difference in their tick rates. Thus for our space traveling observer, As he accelerates at 1 g away from the Earth, not only does his speed relative to the Earth increase causing him to measure a time dilation in the Earth clock, but the Earth is getting increasingly further away in the direction opposite to his acceleration vector. As a result, he would measure an additional increase in the slowing of the Earth clock tick rate. When he changes his acceleration in order to decrease his relative velocity and then accelerate back towards the Earth, the magnitude of the acceleration remains unchanged. However, the Earth's position relative to the acceleration vector does change. Now it is in the direction of the acceleration, and thus according to our traveler, the Earth clock runs fast. This is how the equivalence principle would be applied in this case. One thing to note is that this "equivalent gravity" due to acceleration is only measured by our accelerating observer. Our Earth observer would only measure time dilation due to the difference in relative velocities. (Both observers would also measure any difference due to relative positions in Earth's gravity field, but depending on the exact scenario, this can be insignificant. If you are using scenarios of high fractions of c over light year distances, this additional factor will likely be smaller than the rounding errors in your calculations. )
  43. 1 point
  44. 1 point
    I have never heard anyone else say that truth is as changeable as the wind or that it is subjective and unreliable. Your examples don't show that truth, or right and wrong are arbitrary and decided on a random basis. They show that, not surprisingly, these are complex ideas that have to be tuned to the specific situation. The fact that some people think that truth is relative, not absolute (or, perhaps more accurately, it can be relative) does not necessarily imply that people don't trust truth.
  45. 1 point
    Funny, I was having a long conversation with myself yesterday on this while watching some insignificant movie. I agree with all the premises you layed out in your above post, I would add that however un-empathetic it sounds, the truth is also impractical in many life situations. It is the main reason that I get in trouble when I do when I should have lied or at least keep the truth to myself. I don’t know how somebody can say that the truth is subjective, that is a dead end logic in my opinion, I can agree that it is unreliable though. There is also so many shades of lying and tellig the truth, you can blatantly lie without remorse which is the sociopathic end of the scale or you can empathetically lie about something which saves someone pain which is at the other end of the scale - same with the truth. I think that this is one of those subjects which is so diversly subjective that its impossible to reach any decent consensus when trying to find objectivity which everyone can agree on. The never ending quest of not being an a**hole is on for everybody.
  46. 1 point
    Another way to approach this is to use science as a litmus test. Would it to be good to lie in science, if the lying spares feelings and/or makes you more popular? The answer is no, because we all benefit, collectively, by truth in science, even if that truth means we may have to deal with some neurotic people. Science is converted to engineering which make consumer products, Lying in science can cause serious injuries; the new pill is safe so take it. White lies are a way for the ego, to avoid neurotic reactions, from those who may need to be deceived, so they will shut up. The mother may lie to the child about him being smart, so she does not feel bad, if he feels bad. She is lying for herself, to avoid the discomfort that might be induced by her child because the true may make him feel bad. This is short term thinking. Long term thinking, like in science, would think of the long term consequences of appeasing the neurotic, to avoid your own short term awkwardness. If the mother deceives the child into thinking he was smart, this may win the emotional battle, for both. However, there is no reason for the child to change behavior; study more. Mother may feel better, but her child may go down the road, dumb for life. The both lose the war. Truth is designed for long term thinking, whereas relative truth and white lies is about short term thinking. Truth is important to science since science has a long term vision often connected to consumer products. In politics, the scale is shorter in time, so lies and relative truth make more sense. The lie may only need to last until election time. If there is a negative long term consequences, the politician and fake news, can lie again and again, to buy additional time. If you compare the Conservative approach to the Liberal approach, in terms of time scale, Conservative is about long term values. Liberal is new and cutting edge and is shorter term ideas. Truth would be more useful to conservatives, while relative morality would serve Liberalism better; appeasement. If you look deeper, this breaks down to male and female or conditional and unconditional love. Conditional loves sets long term standards, unconditional changes with needs. We are more feminized in modern times, so relative morality seems to be as valid due to the practical needs of appeasement.
  47. 1 point
    In looking into the background of this report I came across an excellent paper, "Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans". Although this paper is two decades old it gives a clear picture of the landscape of competing ideas into which the Toba eruption global winter and its impact on humanity, was inserted. While doing this speedy literature search I ran across another paper, from about five years ago, that also cast serious doubt on the Toba Eruption/Bottleneck connection. Life being what it is I can no longer locate it. If I find it during a further search I'll post a link here.
  48. 1 point
    Today I learned that plants have a way to use the entire visible spectrum. The literature and our present examinations indicate that the intra-leaf light absorption profile is in most cases steeper than the photosynthetic capacity profile. In strong white light, therefore, the quantum yield of photosynthesis would be lower in the upper chloroplasts, located near the illuminated surface, than that in the lower chloroplasts. Because green light can penetrate further into the leaf than red or blue light, in strong white light, any additional green light absorbed by the lower chloroplasts would increase leaf photosynthesis to a greater extent than would additional red or blue light. Based on the assessment of effects of the additional monochromatic light on leaf photosynthesis, we developed the differential quantum yield method that quantifies efficiency of any monochromatic light in white light. Application of this method to sunflower leaves clearly showed that, in moderate to strong white light, green light drove photosynthesis more effectively than red light.https://academic.oup.com/pcp/article/50/4/684/1908367
  49. 1 point
    I agree with koti; the important thing is to get them asking questions and then, even more importantly, get them to think about how they could answer the questions. Including the importance of doing a rough calculation to check the validity of an idea (even if you have to guess at the numbers involved - e.g. Fermi estimates). In terms of basic physics concepts that would (at the right time) equip them to do this, I think I would choose: 1. Newton's laws of motion (these can be summarised in one sentence, so I am not counting it as 3 things!) 2. The fact we can separate out vector components of force, motion, etc. -- this amazed me when I learnt it and it still seems remarkable! 3. Newton's law of gravitation These three allow you to solve quite a range of real world problems and discover surprising facts (like, all masses fall at the same rate). 4. The fact that some properties are conserved and that this is related to fundamental symmetries (and point out that this was proved by a woman, as science so often seems dominated by male figures) 5. Point out that all the above are only approximations and that they will find out that the real world is actually more complex and more interesting.
  50. 1 point