Hedos

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About Hedos

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  1. [quote name='Lesan' timestamp='1320260754' post='4879816'] Thank you for your answers. It is clearer to me now, even though I still don't understand it. I have this one more related problem that concerns [b]length contraction[/b]. So, a ruler of length 100 cm moves at a relativistic speed and passes near another, stationary, 100 cm ruler. My question is: [b]Will the observers on both rulers see that both rulers have identical length? [/b]That is to say, will there be no length contraction? [/quote] In the frame of reference of ruler A, the ruler B will be shorter. In the frame of reference of ruler B, then ruler A will be shorter. You might be interested in the [url="http://en.wikipedia.org/wiki/Ladder_paradox"]ladder paradox[/url] for a conceptual application of this phenomenon. [quote name='Lesan' timestamp='1320260754' post='4879816'] I mean, is the length contraction just an illusion caused by light lag? [/quote] That's a very good question indeed. I am really not sure, but I would take the point of view that it is "real" (whatever that means), rather than just an illusion, because length contraction is analogous to time dilation which is clearly very "real". Moreover, the ladder paradox above suggests that length contraction IS real and not a mere illusion.
  2. [quote name='Olof Hedman' timestamp='1320244605' post='4879701'] [quote name='Hedos' timestamp='1320186908' post='4879427'] This explains why the clock on the destination planet reads [b]20 years[/b] from the [b]ship-based observer[/b], even though he knows the clock must have only been ticking for [b]15 years since the ship left Earth[/b]. It's because from the ship's reference frame, the two clocks were not started at the same time and the clock on the destination planet has been started [b]5 years before the ship's clock was started[/b]. This part can be calculated using a Lorentz transformation to compare the space-time coordinates of an event in different inertial reference frames. [/quote] Confusing stuff... But you are saying that the guy left on the planet will read 15 years on the same clock? What happens when you land your spaceship? Will the decelleration make the clocks "synchronize", otherwise guy A on planet and B on the ship will have a big problem deciding on a time to meet eachother... If you never land, but have some kind of way to communicate, would guy A and B start to argue about what time the clock is showing? Or would communication be impossible? [/quote] The observer on the planet will read 15 years on the ship's clock, when the ship arrives, yes. This is the same time that the ship-based observer read on the ship's clock. The ship-based observer reads 20 years on the planet's clock and the planet-based observer reads 20 years on the planet's clock. The two observers are in complete agreement. Whether you land the spaceship or not doesn't matter! Nothing would change at all. There is no synchronization involved and there is no contradiction either. Time has indeed been shorter for the observer travelling on a spaceship, there is asymmetry in this situation (because the spaceship undergoes changes of velocity but the planet does not). Keep in mind that when the spaceship has just been launched from Earth, then the reference frame of the Earth and the reference frame of the spaceship disagree about when the clock on the destination planet was started relative to when the ship-based clock was started. But that's because the ship-based clock and the destination planet's clock are physically separated. When the ship arrives at its destination, then because the two clocks are at the same location, it doesn't matter at all which frame of reference you choose, they will all be in agreement about the two clocks.
  3. [quote name='Hodgman' timestamp='1320186530' post='4879424'] [quote name='Lesan' timestamp='1320151999' post='4879222']At the time of launch, [b]two [/b]stopwatch clocks are started simultaneously -- one on the spaceship and one on the distant planet.[/quote]How on earth is this synchronisation achieved ([i]no pun intended[/i])? [/quote] If you know the distance between the planets, you can easily achieve that (in theory). Suppose the distance is 1 light-year. Send a beam of light from planet A to planet B and wait 1 year. After exactly 1 year, immediately start the clock on the spaceship and launch the spaceship (assuming the spaceship can be given a high acceleration burst such that the desired velocity is almost instantaneously achieved). On planet B, start the clock exactly when the light beam is received from planet A. This only synchronizes the watches in the reference frame of the planets, however.
  4. Okay, I think I understand your confusion. For simplicity, let's assume that the ship is going at speed 0.661c relative to the two planets, hence the time and space dilation factor is gamma = 3/4. From the reference frame of the two planets, the ship is moving, hence the ship's clock is ticking slower. With a speed of 0.661c the clock on the ship will show approximately 15 years when it arrives at the destination planet due to time dilation. As others have pointed out, an observer on the planet will read the ship's clock as indicating 15 years too and an observer on the ship will also read the clock on the ship as indicating 15 years. Now, from the reference frame of the ship, however, it is the destination planet that is moving. Hence, the clock on the planet is ticking slower. So at a speed of 0.661c, it is correct to say that the clock on the planet will only have ticked for 15 years throughout the journey and in the reference frame of the spaceship. I think your mistake is to assume that the clock on the planet will [b]read [/b]15 years from the observer on the spaceship. That is wrong, the clock will read 20 years from the observer on the spaceship, as others have pointed out. The problem lies with the notion of simultaneity of events. In relativity, there is no such thing as absolute simultaneity of events. So you cannot say without ambiguity that the two clocks were started at the same time. You need to specify in which frame of reference the clocks are being synchronized. So if the clocks were started at the same time in the reference frame of the planets, then in the reference frame of a spaceship that has just been launched from Earth, the two clocks were [b]not[/b] started at the same time, in fact the clock on the destination planet was started earlier. This explains why the clock on the destination planet reads [b]20 years[/b] from the [b]ship-based observer[/b], even though he knows the clock must have only been ticking for [b]15 years since the ship left Earth[/b]. It's because from the ship's reference frame, the two clocks were not started at the same time and the clock on the destination planet has been started [b]5 years before the ship's clock was started[/b]. This part can be calculated using a Lorentz transformation to compare the space-time coordinates of an event in different inertial reference frames.
  5. Game programming vs Girls

    [quote name='JustinDaniel' timestamp='1320055446' post='4878852'] Damn, Thanks guys , I know problem is by my side but i wanted to know what you guys did when you were at this problem. Anyways, I just talked with her, Ironically we're just friends, She doesn't know that i have a crush on her, Well soon i'd be telling that to her. ( I hope so ) P.S My hormones are raging. [/quote] Just a tip but why don't you ask her out instead? It's a lot less awkward and it achieves essentially the same goal. Moreover, you can make the date as casual as you like which puts a lot less pressure on both of you than telling her about your feelings before you even went on a first date! And think about it from her perspective, if you confess your "love" out of the blues, what is she supposed to respond? Anyway, my advice is to try and go out with this girl as soon as possible so that you can gauge if there is any mutual attraction. So, just ask her out! It's really not worth your time obsessing about a girl if it's not meant to be anyway.
  6. Steve Jobs

    This is a huge loss of a truly brilliant man. RIP steve.
  7. Mini-Contest: ASCII Fishtank

    Good job everyone! I enjoyed playing with everybody's fish tanks! Thanks to capn_midnight for organizing this contest, it was fun!
  8. Relationships

    [quote name='frob' timestamp='1311006775' post='4836871'] [quote name='SteveDeFacto' timestamp='1310884525' post='4836265'] Frob's reply is complete garbage. A psychologist would be a complete wast of money and 2 months is really not a long time to get over a break up. Look at things as they are. You were rejected and being rejected hurts far more than rejecting someone. Your ego was hurt and now you can't help but wonder if there is something wrong with you or something you did. This is completely normal and you will probably continue to feel this way for a few more months. [/quote] I always chuckle when I hear responses like that. Somehow in our society, mental health has become a taboo topic. Similar to how a century ago women couldn't admit to being pregnant, even when they were 9 months along and about to have the child; many people would whisper "Ignore her, she's P.G.", unable to even speak the dirty word "pregnant". Imagine if the OP had said [i]"I hurt my shoulder two months ago. I've done everything I can think of, ice and heat, taking OTC anti-inflammatory drugs, done everything suggested by my friends, now I'm turning to the Internets for help[/i]". There would be the immediate replies of "see a doctor you idiot" along with the obligatory "I spun AIDS" comic. Even if the problem would go away with time, the recommendation would still be to get professional help. But when it is a psychological harm, and it is impairing your life for months on end, there is such a negative backlash against anything dealing with mental health. Physical health? Yeah, see a doctor after it starts impairing your life. Emotional health? Be a man and ignore the pain. Somehow people forget that emotional pain ruins lives and leaves deep scars. If ANYTHING is impairing your life and you can't fix it on your own, you simply get professional help from someone expert in the field. If you have problems with your car and you can't fix it, professional help means a mechanic. If you have problems with your air conditioning and can't fix it, professional help means an HVAC technician. If you can't find an address, professional help means opening a map or using a GPS or asking a local for driving directions. If you have problems with your shoulder and you can't fix it, professional help means visiting your family doctor. And if you have problems coping with a serious emotional event, professional help comes from a psychologist. There is no shame in admitting you aren't perfect or an expert on every topic, and seeking help from an expert whenever you need it. [/quote] Cannot agree with this more. Moreover, you don't need to be mentally ill to go see a psychiatrist. In fact, this couldn't be further from the truth! You can be very happy and still benefit from a few sessions. Indeed, the role of a psychologist includes simply helping to relieve psychological distress and promote your mental well-being and personal development. It's kind of like going to the doctor for a physical or bringing your car at the garage for a routine maintenance.
  9. Relationships

    I used to feel the same as you. I find that as I become more experienced with relationships and more mature in general, this kind of thinking and feelings go away. [quote name='KanonBaum' timestamp='1310871091' post='4836229'] I'm much better off. So much better off and I know it, but then I'll be drifting off in my head and the next thing you know, I'm thinking about it and trying to figure out what went wrong. [/quote] You are probably the worst person to figure out what you did wrong (if anything). Sometimes, especially so for those kind of things, one is just completely blind to what one is doing wrong. Keep in mind that it's quite possible that you didn't do anything wrong, sometimes relationships are just not meant to work because the other person is simply looking for something else. But given that you say this has been a recurring problem, there might very well be some things that you did (and always do) wrong. You could ask a close friend that knows you well about what they think you might have done wrong. Even better if you can ask a female friend. You could also ask the next girl you are dating, once it's serious enough, what are the good things and the bad things about dating you. Keep in mind also that you will get better and better at relationships as you get more experienced. However, I really think you shouldn't obsess about this issue. I certainly hope it isn't making you miserable thinking about your past girlfriend, and if it is I would second frob's idea of seeing a psychologist.
  10. simple ebay question

    I don't think eBay has the capabilities to mix an AND and an OR in a single search, you can only do either. What I recommend is that you do three distinct searches with the option "All words, any order" for: blue cat, brown cat and finally green cat. Then just combine the results together.
  11. How long would a zombie apocalypse last?

    You might be interested in the following (actually serious) articles written by a mathematics professor modeling zombies population using differential equations based on assumptions made from popular zombie movies: [url="http://mysite.science.uottawa.ca/rsmith43/zombies.htm"]When zombies attack!: Mathematical modelling of an outbreak of zombie infection.[/url]
  12. Mini-Contest: ASCII Fishtank

    Alright, here it is: [url="http://www.megaupload.com/?d=L6KFJJER"]Hedos' Fishtank[/url] Hint: The game can become quite a bit of a huge mess if you drop too much food One fun way to play this game in fact is to not do anything at all and just watch the fishtank evolve given the initial setup. There should cycles where the population of fish alternate between going almost extinct and then growing very large. It's interesting to see how long your fish can survive without any intervention. If you do that however, make sure to toggle on the fast mode. Anyway, the fact that the fishtank behaves as some kind of an ecosystem with population cycles is what I'm most proud of! I really regret not adding the remaining features I had in mind. I wanted somehow to be able to export or visualize statistics (number of fish, quantity of plankton, etc.) so that one can see clearly the alternating cycles that the ecosystem goes through (inspired from the prey-predator cycles, where both populations oscillate but the predator population always lags the prey population). Also, I really wanted to add algae! I couldn't figure a proper way to have the algae grow or interact with the fish though.
  13. Mini-Contest: ASCII Fishtank

    Unfortunately I wasn't able to work on my fishtank in the last few days and hence missed the deadline. The game is far from finished, but I'd like to submit it anyway so that people can have a look. I have however to make a few very quick final adjustments to the game (otherwise it won't be playable) and then I'll submit it in the next hour or so. I totally understand if that means I'm out of the contest, that's okay.
  14. My reasoning is more than yours

    For Question 1, I thought of cutting a giraffe into pieces at first, but then I realized that the better idea is just to find a large enough refrigerator and put the giraffe in. My answer for question 2 was the same, which I stand is correct, because the question asks "How do you put an elephant into [b]a[/b] refrigerator?". The assumption that you have to put the elephant in the same refrigerator as the giraffe is just arbitrary and plain wrong! I got question 3 right, I thought this was pretty obvious given the provided answers to the two previous questions... For question 4 though, I have to admit I completely missed the point, but my idea was if there is a bridge, just cross it, and otherwise ask the locals how they do it. Edit: Yes I do realize the quiz is silly
  15. Mini-Contest: ASCII Fishtank

    I'm going to enter this contest. I have some free time this month, plus this looks like fun I strongly suggest anybody that's willing to participate to have a look at [url="http://www.benryves.com/tutorials/winconsole/"]Benryves' Windows Console[/url] tutorial to learn how to setup a 80x25 or 80x50 console window without a scrollbar, with no flickering and with user input. So far I have bubbles and one type of fish that only moves in a straight line