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Thread: why not

  1. #1 why not 
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    i know u guys a really sick of simaler questions like this but im going to ask anyway please dont flame me. but its said even if you can travel at 50% light speed next to say a beam of light it will still be moven away from u at the speed of light why is this. if to cars for example travel towards each other at 50kmh the combined speed is 100kmh. then when to beams of light are going towarads each other wouldnt that make the combined speed double light speed.
    i thought the speed of light was not a speed limit.
    can someone please try explain why its a constant speed even if you are doing 99% of its speed.. i never studied physics i wish i did now but it seems very complicated. so sorry if this is anoying question


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  3. #2  
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    The bottom line is that the speed of light isn't a speed. It's a velocity. There's a big difference. Have you ever heard the expression no time passes for a photon? It's true. If you go real fast you experience less time. That's what Special Relativity is all about. A photon travelling at c experiences no time. This means that as far as the photon is concerned, speed = distance over time, and a time of zero means its speed is infinite.


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  4. #3  
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    Quote Originally Posted by Farsight
    The bottom line is that the speed of light isn't a speed. It's a velocity. There's a big difference. Have you ever heard the expression no time passes for a photon? It's true. If you go real fast you experience less time. That's what Special Relativity is all about. A photon travelling at c experiences no time. This means that as far as the photon is concerned, speed = distance over time, and a time of zero means its speed is infinite.
    velocity infers no particular speed. using mirrors you can bounce that light back and forth, it goes nowhere but at the the constant speed of 186kmps.

    i think his question relates to understanding the cum effect of speed to another object. maybe he should have stuck to the cars.
    if you travel at 25mph and one is in front going 50mph verses one going 100 mph. the time before the object (car) is no longer visible will take 3 times longer for the slow car. the same would be true moving along with a beam. that one particular beam (not the light), would take additional time to vanish according to your speed. the actual speed still that 186k mps hasn't changed.
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  5. #4 Re: why not 
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    Quote Originally Posted by Tommy4711
    i know u guys a really sick of simaler questions like this but im going to ask anyway please dont flame me. but its said even if you can travel at 50% light speed next to say a beam of light it will still be moven away from u at the speed of light why is this. if to cars for example travel towards each other at 50kmh the combined speed is 100kmh. then when to beams of light are going towarads each other wouldnt that make the combined speed double light speed.
    i thought the speed of light was not a speed limit.
    can someone please try explain why its a constant speed even if you are doing 99% of its speed.. i never studied physics i wish i did now but it seems very complicated. so sorry if this is anoying question
    Here's a simple explanation, Light travels 300,000km/sec - if you travel at 50% of the speed of light then time will (for you) slow by half) so now your stopwatch when it says 1 second, the light has travelled 300,000km
    so it appears to you to still be travelling at the full speed.

    The guy standing still also see's it travel at 300,000km/sec as his watch reads a 'true' second.

    It's all down to a thing called 'time dilation'.
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  6. #5  
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    ok thanks good explanations.
    curious whats the fastest we have been able to move any type of matter.
    anything close to light speed?
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  7. #6  
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    I think the odd proton has come close to it in one of the accelerators, try the cerne web-site it might give a clue. On the larger scale we have chucked things around at no more than 10-20Km/ second most of these speeds though achieved in space. If you have a TV or PC with a tube rather than an LCD display, the beam of electrons which strikes the phosphor atoms on glass and produces photons is (if I remember correctly travelling forwards at up to 40% of the speed of light, and if your screen is 25inch 1000 lines 30 frames/second then the 'sideways' sweeping of the beam is around 18 miles per second, and on the 'flyback' is around 90 miles per second.
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  8. #7  
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    Check out ultra-high-energy cosmic rays, tommy:

    http://en.wikipedia.org/wiki/Cosmic_ray
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  9. #8  
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    so with time dialation my monitor is probably only half as old as i thought it was lol.. ok my next question.. i dont really know the laws of relativity or special relativity but basicly it tells us there is no way we could travel the speed of light, please correct me if i am wrong because i really have no idea. now lets say we descover say a black hole in space, and say we fly something into it. wont it travel in faster then the speed of light and break these laws. because a black hole is something that has so much gravity that not even light can escape it.. and what happens with time dialation here. lets say we did try shine a light out of a black hole if we ever did see it wouldnt we see it forever.. anyway see if you can explain it to make sence for me please. as you can tell i dont know alot about it but i am very intrested. everytime i try look anything up its explained as if i should allready know what im reading thabnks guys
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  10. #9  
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    The real answer is - we don't know what happens beyond the event horizon, it's all guess work, like I show you a sealed box that weighs a kilogram and rattles when you shake it, you guess it's a brick, but it could be a parrot or a cassete/mp3 player o an alien or a bomb or.......

    We believe the laws of our universe 'breakdown' at this point, though the truth is probably that the laws of the universe don't breakdown - it's just we don't have the right laws that include what happens there.

    Black holes have not yet proven to exist, although there is a lot of mathematical and some observational evidence that strongly points to their existence.

    As for reading up on it, you just have to read as many different accounts as you can, either you then get an insight (not everbody does) or you give up, to understand it, takes a big leap of faith, you have to just 'accept' concepts that are alien to you, and maybe....

    There are lots or different theories in cosmology, like open/flat/closed universe, we don't know the age of the universe, when anybody says a star is 'x' light years away, they mean +/- 50% but never say it, oddly enough we don't even know what's at the centre of our own planet! - we just have a model we think accounts for the way it behave, nobody understands gravity, electricity, photons - again we have models that predict behaviour but that's it. We dont know why the universe is expanding, or the rate of expansion, or even what's in it! as only about 2% is visible to us (if I remember correctly) 80% is missing, galaxies don't behave the way they should - hell I could go on all night!

    I'll probably be crucified for this post.

    So don't worry about it, it'll probably all change in a few years, when it will get probably get a lot more complex...
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  11. #10 Re: why not 
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    Quote Originally Posted by Megabrain
    Here's a simple explanation, Light travels 300,000km/sec - if you travel at 50% of the speed of light then time will (for you) slow by half) so now your stopwatch when it says 1 second, the light has travelled 300,000km so it appears to you to still be travelling at the full speed.

    The guy standing still also see's it travel at 300,000km/sec as his watch reads a 'true' second.

    It's all down to a thing called 'time dilation'.
    Almost megabrain. If you are traveling at 0.5c relative to some other inertial observer then 1 minute to him on his clock corresponds to 53 seconds on your clock . This distinction is important as time doesn't slow down for you and you notice noting spectacular when traveling in a black box at 0.5c relative to someone else (we are doing that right now) - but compared to some other observers notion of time our clocks are running slower, as theirs appears to be doing as observed by us.

    Length contraction and time dilation always conspire together to insure that every inertial observer measures the speed of light to be c. It is a good exercise in special relativity to check that fact.
    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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  12. #11  
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    Tommy: time dilation is the wrong approach. There is no fundamental "stuff" out there called time to get dilated. All that's happening is that your experience of time changes. If you could travel at c you would experience no time, and because Speed = Distance / Time you would perceive your speed to be infinite. That's why "the speed of light" is a misnomer, it's not really a speed. If you keep on thinking of it as a speed, you tie yourself up in all kind of knots.

    As megabrain says, Black Holes aren't actually proven. But people are pretty confident that they're out there. The trick is to imagine yourself falling into a black hole from an "infinite" height, so you've got all the time in the world to accelerate faster and faster and faster as the black hole pulls you in. The place where your velocity reaches c is where you cross the event horizon. To get out of the black hole now, you'd have to stop, turn around, and fire your rockets until your velocity is c going the other way. But you can't stop, and even with unlimited fuel you can't go faster than c. It's a one way street. There's no going back. All directions lead into the centre of the black hole. Aw, it's weird.

    It gets weirder. Because when you were falling into the black hole, I was powering up my rockets. As you fell faster and faster I was just starting my burn. And just as you were passing the event horizon, I overtook you at a blistering clip. You were travelling at c, and as far as you were concerned, my speed was infinite.

    There are some marvellous things in physics. But you just can't see them if you think light has a speed. It doesn't. That's what Special Relativity is all about.
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