Speed of light question

Discussion in 'Physics & Math' started by LuckAse, Feb 7, 2010.

  1. LuckAse Registered Member

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    Why is the speed of light such a stigma for space travel and whatnot.

    Isn't it just a speed. Shouldn't it be irrelevent in space? Or is there some sort of barrier that there is no possible way to go faster than that??
     
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  3. DRZion Theoretical Experimentalist Valued Senior Member

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    Well, yes, the speed of light is widely considered to be as fast as one can go.. but this isn't really the limiting factor in space travel - nothing we can build right now can even approach the speed of light.

    However, if you do build such a 'relativistic' space ship (one which can go close to the speed of light) and your only dream is to explore space you can still do this going slower than the speed of light. The more you accelerate the ship the sooner you will get there even though it seems like there is a limit.

    The reason that you can still get there faster is that as you approach the speed of light c time begins to go by slower for you. And as time goes by slower, the universe around you will begin look like it is contracting in the dimension in which you are travelling.. It will seem as if the star, planet, cluster, whatnot you are trying to reach is getting closer as you go faster because of relativistic effects.

    The problem is that if you ever want to make it back and report your results you will find that a large amount of time has passed since you left and that it would be vary difficult to actually coordinate missions and such things in space if there was no hope to make it back to the world in which you were born. You would come back 30 years older but the earth would have aged thousands of years.

    Essentially, you can still explore space in a ship that goes slower than light but its not something that could be incorporated into society because of the huge amount of time it would take to travel between stars.
     
    Last edited: Feb 7, 2010
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  5. MikeO Registered Senior Member

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    I'd say that the speed of light is just the opposite of a stigmatized speed.

    It's a hallowed speed.

    At the very logical beginning of Relativity Theory it's regarded as a LAW, that light travels at that one SPECIAL speed, ALL the time, no matter what, in vacuum. This was in response to all the experimental data, the most famous being the Michelson-Morley experiment.

    It's assumed. It's a Postulate. All else is derived from it.

    In that logical derivation following this assumption, Space and Time literally bow down to this special speed, and that's why I called it hallowed.

    The speed of a source of light and the speed of an observer cannot affect it. Classical notions of space and time must "re-adjust" themselves (Lorentz transformations) to make sure the measured speed if any photon is always the same for all observers, regardless of any relative speeds or multiple observers, or source speed.

    Any attempt to go beyond the speed of light is matched by space, time, mass and energy algebraic "adjustments" to prevent it.
     
    Last edited: Feb 7, 2010
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  7. LuckAse Registered Member

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    Wait so your saying if you go faster than light then you are speeding up time it self. (for you atleasat)

    I have never heard of this theory.
     
  8. MikeO Registered Senior Member

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    If you TRY to go up to the speed of light, all kinds of things happen, time slowing is one of them. This is what Einstein's Theory of Relativity is, at it's very beginning.

    To put it a little more accurately, if you try to make an object go very fast, time on that thing slows down. For you, the object measures a little more massive, and it seems to resist your effort to make it go faster. The math (Einstein's) by which this adjustment happens says that you can't make it go as fast as light. The closer it gets to light speed, the more massive it gets and you soon run out of energy needed to get it to go faster.
     
  9. LuckAse Registered Member

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    Well lets just say we had a propulsion system that had basicly unlimited power, and that system kept going faster and faster. so as soon as it hits the speed of light its going to be slowing down time.

    So if you had a ship that went 3.1536 * 10^3 times lightspeed then you could travel a lightyear a second, which inturn means to you. you would be in that amount of time, but to everyone else you would be gone for a year?
     
  10. MikeO Registered Senior Member

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    What's the difference between having a proplusion system that has "basicly" unlimited power, and one that has "plain old garden variety" unlimited power?
     
  11. LuckAse Registered Member

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    Nothing is unlimited except for cycles and space.... Thats the only reason i said that...
     
  12. BobG Registered Senior Member

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    Remember that in special relativity you can only speak of the relative velocity of two reference frames. So a more useful way of thinking of it is that there is a limit to how fast we can observe another body with mass move at. So the example of a ship traveling to a star 10 light years from Earth it would not be possible for them to travel there and back in less than 20 years.

    However for someone on the ship there is no theoretical limit to how quickly the journey would seem to them. This is not because it is possible for them to measure the Earth moving away from them faster than the speed of light but from their reference frame the distance to the star gets shorter due to length contraction.
     
  13. Pete It's not rocket surgery Registered Senior Member

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    10,167
    There's no limit to rapidity, to momentum, or to kinetic energy.
    And the higher those go, the closer your speed gets to light speed. If you could have infinite momentum, kinetic energy, or rapidity, then your speed would be the speed of light.

    Try this:
    Einstein Light "the finer points of relativity in less time than it takes to eat a sandwich."
     
  14. MikeO Registered Senior Member

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    LuckAse,

    By asking you about "basically" unlimited power I was trying to show you that all power IS limited. It just doesn't get you anwhere in science to start off a question with any kind of unlimited power. That's science fiction, not science.

    If you have a space ship, it has only so much power, and then it runs out of gas.
     
  15. LuckAse Registered Member

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    Ya i understand that. I was saying if there was something capable of propelling something as fast as light.
     
  16. MikeO Registered Senior Member

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    There are two "somethings" in your last sentence.

    If you tell me the mass of something#2, and how much power is in the "capable" something#1, then the equations will tell you how fast something#2 will go, assuming no wasted energy.

    That calculated speed will always be less than light speed. The math sez so.

    If some energy is wasted in the effort, as it always is, then the speed of something#2 will be even less than the first calculation.

    The math that rules all this is simple algebra. No calculus is needed.
     
  17. LuckAse Registered Member

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    86
    What if we build a cannon on mars that would be the size of austrailla reaches into space. And just say it could lunch a projectile at light speed. The projectile being a human ship. Once it was in space it would have no reason to slow down as long as it dosn't hit any suns, black holes, etc.

    So then if we discovered a habitable planet. We could colinize this way...

    Is this at all plasuable (not considing the way the cannon thing projects them)

    What im asking mostly is that nothing is going to slow down an object at light speed is it? like letting of the gas of a car.....is what im comparing it to.
     
  18. Pandaemoni Valued Senior Member

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    3,634
    The problem is that no cannon can shoot a projectile with a mass at the speed of light.

    Imagine that you had a rocket, and that all the energy in the universe were at your disposal to power it. The faster you go, the more energy the rocket has. The more energy the rocket has, the more massive it becomes (because E=mc^2, or conversely m=E/c^2). The more massive it becomes, the harder it is to accelerate.

    Relativity (or the lorentzian transformations) shows that, in order for a particle (be it a rocket or a single proton) to reach the speed of light, you would need an infinite amount of energy, because at the speed of light that massive object would an infinite mass. The universe itself has only a finite amount of energy (vast though it is).

    If the rocket had no mass (like a photon has no rest mass), then it could travel at the speed of light.

    Worse, the closer to the speed of light you get, the more time slows. If you were very close to the speed of light, the entire Stelliferous Era could be over in the blink of an eye, and there would be no stars left, no new stars forming and no planets to colonize.
     
    Last edited: Feb 7, 2010
  19. MikeO Registered Senior Member

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    LuckAse,

    Pandaemoni is right. It sounds more and more like you want a science fiction forum in which to pose your questions. If you want people to play along it's got to be in the fictional category, because that where you insist on beginning.

    Aside from humor and a minor amount of eccentric stretching (like my bringing up but not dwelling on Frank Tipler on another thread:bugeye

    Please Register or Log in to view the hidden image!

    , we're just not here to play the type of game you are proposing.

    I suggest you learn some basic Phyisics to play here or find a SciFi forum where you can run wild.
     
  20. CptBork Valued Senior Member

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    6,460
    In particle accelerators and colliders, the whole point is to inject an enormous amount of energy into a small number of very light particles. For example, the beam circulating around the LHC will roughly have as much power in it as a 500lb. bomb like the ones dropped by the US air force. Yet if you took all the particles in the beam and bunched them together under a microscope, the whole collection would still be too small to see.

    In effect, a particle accelerator is like the "Australia-sized cannon", but the objects being shot out of the cannon are subatomic particles instead of spaceships. You put in a large quantity of energy, you get particles going at \(0.999c\). Add more energy in, and they go up further, to \(0.9999c\), and so on, getting closer and closer to the speed of light without ever actually reaching it. The relativity equation \(E=mc^2\) says that energy and mass are equivalent, so the more energy you add to the particles, the heavier they get, and the more energy it takes to continue accelerating them towards the speed of light. Relativity says you need an infinite amount of energy to reach the speed of light (unless you have wormholes or some other hypothetical non-kinetic means of propulsion). Even though particles in our accelerators reach as close to the speed of light as they do, we accelerate them because we want to smack them together at high energies, not because we want them to be travelling near lightspeed.
     
  21. LuckAse Registered Member

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    I am not trying to play a game, im trying to learn. And i learn best in social situations. If you don't want to discuss then don't post. Isn' t it that simple?
     
  22. Read-Only Valued Senior Member

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    10,296
    Don't worry about people like that. The problem is they are used to seeing cranks here who post nonsense and sometimes they can't tell the difference between those people and the ones who really want to learn something new.

    Let me take a shot at it for you: The speed of light IS a limit, not something like the speed of sound that can be broken. It's one of the few true limits in the universe - just like Absolute Zero. You can't get any colder than Absolute Zero and you cannot travel faster than the speed of light.

    And to be more accurate, you, I, a spaceship or anything that has mass cannot even reach the speed of light.

    And the reason is very straightforward. It's a logarithmic scale - meaning in order to just gain a little more of something you have to put MUCH more of something into it. In this case, it's speed and energy. Let's assume you have enough energy to get your ship moving at 10% the speed of light. To get it up another 10% would require THOUSANDS of times of more energy than it took to get that first 10%!! See where this is going? It's all because your ship is actually gaining mass as you go faster. And I'm sure you understand it takes a lot more energy to double the speed of a freight train than it does to double the speed of a car.

    To actually get an object with mass to reach the speed of light would require an infinite amount of energy (which, of course, is impossible to get) and that's all because your ship now has infinite mass. It a no-win case.

    Does that help, or does it still leave you with a question?
     
  23. skaught The field its covered in blood Valued Senior Member

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    4,103
    Einsteins equations. E=MC2. Energy equals mass times the speed of light squared. A traveling body has more mass than a body at rest. And the faster a body is traveling, the more mass it has. Light has no mass. Therefore, it is not bound by this rule. Therefore, it is the cosmic speed limit so to speak. A body that has mass, say a spaceship, Requires energy to propel it, and it also contains more energy, which is converted to mass. The faster it goes, the more energy is required to propel it. As it approaches light speed, the amount of mass it has approaches infinity, and therefore it requires infinite energy to propel it. It is impossible, thus far, to exceed infinite energy. Therefore, a traveling body that has mass, cannot exceed or reach light speed. At least not with current technologies.
     

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