Tuco
I got Tuco'd!
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The Astronomy Thread
- Thread starter Araxen
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bro.
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Just look at you go today.
Chanur
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Chanur
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The universe might not change but our understanding of how it works sure as hell does.
Kharzette
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Forget the flawed outside observer formulae and just think about the basic fundamental principle of relativity: Speed is relative.
Lets say you boost up to 0.5 C from the perspective of an earth goer. Now shut your engines off. From the ship side perspective you are standing still and earth is moving away at 0.5 C.
Now switch them back on. Is it any harder to accelerate from what seems to be a standstill than it was when you left earth? It's the same at higher relative speeds as well (though you do get a bit of drag inside galaxies from hydrogen atoms).
You can just keep accelerating like that for years if you have the juice to do so. There is no speed limit.
The only difference is the hour hand on clocks back home would be spinning faster. A 20 year trip out to the great attractor would mean many millions of years go by back home.
Fucker
Log Wizard
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It is entirely possible that our misunderstanding of the universe alters how it works. I call it George Floyd's Theory of Surreality.
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Yes, it is. That's an easy one.
Closing your eyes doesn't make your ship go faster. Neither does painting them red. But you could give it a shot and see which one helps more
To give a shitty analogy that doesn't match the physics but is easy to visualize, take a car to the top of a really big hill and start going down it, throw it in neutral and coast. Now throw it back in gear (let's ignore transmission gearing for a second). Once in gear press the gas... nothing happens, you don't just start adding acceleration, not until your engine matches the existing power and can start to turn the shaft.
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Burns
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What do you mean there is no speed limit? The speed of light is the speed limit and you can never reach it, even with infinite energy/power. If you use the example of 1g acceleration, after about a year it starts hitting huge diminishing returns. So much so that it would not be worth hauling the fuel to stay at 1g after a certain timeframe (probably).
Captain Suave
Caesar si viveret, ad remum dareris.
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This is correct. Relativity is such a mindfuck and overturns the most basic heuristics used by our brains. Reality is deeply, deeply weird.
Distance, time, and mass-energy all trade off against each other. From the perspective of the accelerating observer you experience 1G (or whatever) "forever". The acceleration continues to add kinetic energy to your mass-energy total, which compresses your perception of spacetime in front of you and reduces the perceived distance between you and what you're traveling towards so you don't violate c. You see massive blue/redshift along your direction of travel (the CMB will look like a gamma ray burst and fry you). While you hit c from your perspective, an infinite amount of time has passed for the outside universe. A non-accelerating observer will see you asymptotically approach c due to the time dilation.
For a finite example, if you tried to go to Andromeda at 1G from your internal perspective you could make the trip there and back in less than 60 experienced years. You'd find that six million years had passed on Earth, though, and you never violated c relative to any observers. For you it was a shorter distance, and for them it was a longer time.
Anyone really interested in this should read this book. It does a great job explaining relativity if you can tolerate a small amount of math.
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Cybsled
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Based on relativity, there is diminishing returns to acceleration. The closer to light speed you get, the greater the energy cost as a function of your mass. For that reason it is thought that nothing with any large mass (like a starship) can be accelerated to the speed of light realistically
Even if you kept accelerating, your speed in theory would just be adding more fractions of a percentage towards C, but never actually reaching C.
Even if you kept accelerating, your speed in theory would just be adding more fractions of a percentage towards C, but never actually reaching C.
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Captain Suave
Caesar si viveret, ad remum dareris.
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This explanation was popular for a while but I think it was a shortcut to get around having to explain the weirder parts of relativity. "Increasing mass" sort of applies an intuitively palatable reason why you couldn't accelerate to c from the perspective of an outside observer, but it's not what's literally happening from the perspective of people on the ship. (Relativistic mass includes kinetic energy.) I've got a friend who is an an experimental astronomer and he says these days the preferred explanations stick to time dilation and length contraction.
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That's great to explain what you the star ship passenger experience but it's actually not what is being discussed.
You are limited in how much you can accelerate regardless if you are an outside observer or not. Closing your eyes doesn't change how much you can accelerate or the energy required to continue to accelerate.
Kharzette thinks that you can add acceleration (via engine thrust) to a point, lets call it 0.5c which she used as an example, turn off your engines, and then close your eyes. From an outside observer you the starship have a velocity of 0.5c, but from within the spaceship you are motionless. Then you turn your engines back on and can add more acceleration starting from 0 (not from 0.5c) and accelerate again, up to 0.5c, then turn off your engines. You only needed the energy to accelerate to 0.5c two times, not the energy required to accelerate to 1c. In her explanation, you can continue to close your eyes, turn off your engines, and reset your speed to 0 as many times as you want, and achieve speeds many many times the speed of light....by closing your eyes.
This is not how the math works. no need to bring time dilation into it, we're talking about the fundamentals of how propulsion works, talking newton's first laws here not anything more complex.
Your speed increases your mass, which increases the amount of thrust you need to add in order to add acceleration. Regardless of the observer. The amount of thrust you need to add to increase speed will increase exponentially as you approach c. You can't "reset" it by closing your eyes.
edit: Oh ok I think i'm misunderstanding her point. She is talking about relativism of the spaceship, not the closing your eyes thing, my bad. Yes if you could accelerate to almost c, you could cross the galaxy in 12 years ship time but in real time it would be like 150k years. You can't really use this as a method of colonizing the galaxy though.
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Captain Suave
Caesar si viveret, ad remum dareris.
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That is how it works, though, at least assuming you had a propulsion system that could provide velocity-invariant thrust. It's the same amount of energy, not that you could ever expend it. The trick is that as you approach c for you space compresses to zero distance and for everything else your time stretches to infinity. As you hit c from your perspective the universe has ended.
It increases your relativistic mass-energy which effects your experience of space-time, not your rest mass. Newtonian mechanics break down.
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Burns
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My impression is that it is more like a spaceship that is traveling on a huge strip of rubber. You can apply the same amount of thrust to achieve 1g (if that's the target), but the closer you get to c, the more stretched out spacetime gets. Meaning the individual experiences the same 1g, but the ship does not travel as far per unit of energy. This "slowing" happens more and more the closer you get to c.
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I'll let her clarify her position i'm still confused on it, well particular this:
Whether you describe it as time or mass approaches infinity doesn't really matter, the point is that energy required to accelerate to c is infinity in either viewpoint
It sounds like she thinks you can just keep turning it off and turning it back on and continue to accelerate past c, which is false.
Whether you describe it as time or mass approaches infinity doesn't really matter, the point is that energy required to accelerate to c is infinity in either viewpoint
Furry
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The biggest issue mathematically with the lorentz transformation is that if you hold that it takes more energy to accelerate the closer you get to C, an extremely finely tuned gyroscope would be able to detect what neutral speed is, which defeats the entire purpose gallileo's boat. To put it simply, if it takes more effort to accelerate toward C, then in any frame of reference you should be able to accelerate more easily toward C, rather than away from it. The closer you get to C the more notable this effect would become.
It kinda ruins the whole point of relativity, but the math predicts it as stands. Not something we'll likely be able to test for anytime soon, since our frame of refrence likely isn't a substantial way towards C, so relativity goons are safe for the moment.
Cad
scientia potentia est
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I thought the way it worked was that the people on the ship can experience a 1g acceleration essentially forever, and time dilation means as they crowd the speed of light more and more they will seem to go faster even if to an outside observer their acceleration starts to slow. To the ship that can produce a 1g acceleration in space, it would experience (on board the ship) a 1g acceleration all the way to .99999999c, right? But to an outside observer its acceleration would start to slow down at some point.