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Old 12-13-2011, 07:51 AM
 
Location: Hiding from Antifa?
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If the nearest possible planet capable of sustaining any form of life is 600 years away, then we probably have at least 1100 years left, before another life form discovers our first radio transmissions powerful enough to be seen, and then travels here to see what we are all about.

Looking at human nature and other life forms on this planet, I don't hold out much hope that these other, curious, life forms will be all that friendly to us. Besides our own human instincts, most life forms on this planet survive because they have innate fear of anything different. Look at the known life forms here that have gone to extinction, and you will probably find that they did not have the proper amount of instinct to get away from other, more dangerous, life forms and thereby died off. A little fear might be a good thing when it comes to letting other life forms know we are here.
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Old 12-14-2011, 08:59 AM
 
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Originally Posted by eskercurve View Post
The meaning is, if we had the ability to go 90% the speed of light, and went to the nearest star, Alpha Centauri, it would take roughly 5.5 years to get there according to a person on the Earth, but to a person on a spaceship going there, it would only take 2.75 years, assuming instantaneous acceleration and stopping.
to
That's the example and answer as that's what i was trying to allude at .

O.k. another thought here is that since mass expands by a factor of 2.7 at the speed of light i could percieve how we could create a spacecraft to survive that journey as i'm guessing something akin to an mimetic poly-alloy (remember T-1000 in Terminator 2) however how could a human survive that journey as the expansion ''should'' kill them?
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Old 12-14-2011, 01:04 PM
 
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Originally Posted by 6 Foot 3 View Post
That's the example and answer as that's what i was trying to allude at .

O.k. another thought here is that since mass expands by a factor of 2.7 at the speed of light i could percieve how we could create a spacecraft to survive that journey as i'm guessing something akin to an mimetic poly-alloy (remember T-1000 in Terminator 2) however how could a human survive that journey as the expansion ''should'' kill them?
Part of the problem is that it changes both space and time. It's probably impossible to reach the speed of light for a number of good reasons. Even at a speeds near the speed of light, time and space change from the perspective of the traveler. The journey over vast distances would seem to be almost instantanious. If you could almost reach the speed of light, you could cross the universe in almost an instant. I have no idea exactly how you would control a spacecraft to reach a specific destination at such enormous speed. I should mention that it isn't that time and space in the universe change, it's that time and space for the traveler changes. That relates to the earlier point that it differs from the point of view of the observer, whether the observer is stationary or is the traveler.

The speed of light as the fastest anything can travel only pertains to things within the structure of the universe. It does not necessarily pertain to the expansion of space which can exceed the speed of light. If the speed of light is the maximum limit, then it would mean reaching a point where time and space are equal to zero. Time completely stops. Space has no length.

Back to the idea that it would take 600 years to reach Kepler-22b traveling at the speed of light, it's worth keeping in mind that's based on our point of view back here on Earth. If the traveler made a return trip back to the Earth, he would find the planet is 1200 years older than when he first departed.

Another big problem with traveling at or near the speed of light is the amount of energy required to do that. It mght require as much or more energy than there is in the entire universe. You'd need a REALLY BIG spacecraft. LOL!

Here are some interesting non-technical views by astrophysicist Ethan Siegel on the subject.

Q & A: The Speed of Light | Starts With A Bang!
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Old 12-14-2011, 10:11 PM
 
Location: US Empire, Pac NW
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Originally Posted by 6 Foot 3 View Post
That's the example and answer as that's what i was trying to allude at .

O.k. another thought here is that since mass expands by a factor of 2.7 at the speed of light i could percieve how we could create a spacecraft to survive that journey as i'm guessing something akin to an mimetic poly-alloy (remember T-1000 in Terminator 2) however how could a human survive that journey as the expansion ''should'' kill them?
According to physics, F=ma. "a" is acceleration and "m" is your weight (technically your mass), and F is the sum of the total forces on the mass.

So long as your material is strong enough, it can survive the acceleration to near light speed just fine, then once you're there, it has no forces acting on it at all, so surviving near light speed is not a problem at all. The only problem is speeding up in a meaningful amount of time requires a constant 1g or 2g acceleration for up to a year straight! That means if you weigh 180 lb, then for a full year you will need to survive living in a space which is very VERY hard to move around.

After all, we have airplanes that survive 10 g's of force for the military regularly.

If you have a robotic explorer, it doesn't matter as much. Normal metals we have today could survive the journey. It does, however, compound the problem of acceleration.
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Old 12-15-2011, 12:11 AM
 
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Originally Posted by eskercurve View Post
According to physics, F=ma. "a" is acceleration and "m" is your weight (technically your mass), and F is the sum of the total forces on the mass.

So long as your material is strong enough, it can survive the acceleration to near light speed just fine, then once you're there, it has no forces acting on it at all, so surviving near light speed is not a problem at all. The only problem is speeding up in a meaningful amount of time requires a constant 1g or 2g acceleration for up to a year straight! That means if you weigh 180 lb, then for a full year you will need to survive living in a space which is very VERY hard to move around.

After all, we have airplanes that survive 10 g's of force for the military regularly.

If you have a robotic explorer, it doesn't matter as much. Normal metals we have today could survive the journey. It does, however, compound the problem of acceleration.
Speaking of G force, an article in NOVA (link below) says fighter pilots handle 8 or 9 G's. During prolonged periods they wear anti-G suits that inflate to keep the blood in the upper body. Space shuttle astronauts experience less during launch with little to no problem. A good part of it is the design of the seats. Re-entry can be a problem though after having spent time in micro-gravity. The article also recounts the rocket sled tests of John Stapp who experienced an astonishing 46.2 G's. "For an instant, his 168-pound body had weighed over 7,700 pounds." Almost 4 tons! As you indicated, it's not so much the speed that's the problem, it's the acceleration, especially rapid or prolonged acceleration.

NOVA | All About G Forces

Human Spaceflight


Quote:
So long as your material is strong enough, it can survive the acceleration to near light speed just fine, then once you're there, it has no forces acting on it at all, so surviving near light speed is not a problem at all. The only problem is speeding up in a meaningful amount of time requires a constant 1g or 2g acceleration for up to a year straight! That means if you weigh 180 lb, then for a full year you will need to survive living in a space which is very VERY hard to move around.
I'm not sure what you mean here. Are you saying it would only take up to a year of accelerating at 1 to 2 G's to reach light speed? 1 G would be the G-force normally experienced on Earth by a stationary object. Or do you mean in constant increments?
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Old 12-15-2011, 09:09 PM
 
Location: US Empire, Pac NW
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Originally Posted by NightBazaar View Post


I'm not sure what you mean here. Are you saying it would only take up to a year of accelerating at 1 to 2 G's to reach light speed? 1 G would be the G-force normally experienced on Earth by a stationary object. Or do you mean in constant increments?
1-2 G's constant acceleration. Remember, in space, you're at 0 G relative to earth's gravitational pull (we're still being pulled by the sun but it's all relative anyway with light speed). So 1-G would be 9.8 m/s^2 constantly.

The speed of light is 3 x 10^8 m/s in velocity. If we accelerate at 1 G = 9.8 m/s^2 constantly, it would take approximately 30,600,000 seconds to reach light speed, which is roughly 354 days.
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Old 12-17-2011, 11:39 AM
 
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Originally Posted by eskercurve View Post
1-2 G's constant acceleration. Remember, in space, you're at 0 G relative to earth's gravitational pull (we're still being pulled by the sun but it's all relative anyway with light speed). So 1-G would be 9.8 m/s^2 constantly.

The speed of light is 3 x 10^8 m/s in velocity. If we accelerate at 1 G = 9.8 m/s^2 constantly, it would take approximately 30,600,000 seconds to reach light speed, which is roughly 354 days.
Thanks. I have to admit it makes my head spin. I had to do a little hunting on the subject. I agree with the point you made, but help me out here. How that would work in a practical sense with regards to an interstellar spacecraft traveling at or near the speed of light?

The speed of light in a vacuum is roughly 186 thousand miles per second, which is almost 670 million miles per hour. That's the top-most speed light can travel under ideal (perfect) conditions which assumes there's nothing else to interfere with it. We can assume that the expansion of space of the universe is not bound by the speed of light. As such we can assume that the speed of light applies to everything known in the universe.

For our interstellar starship, we'd have to take into consideration that the speed of light is fine for massless particles like photons. The big problem is that there's a lot of stuff in the galaxy, as well as universe, such as gasses, dust, solid objects, atoms, etc. The speed of light isn't constant in all materials and can be slowed down. Protons have been accelerated to near light speed by particle colliders under very controlled conditions, but still not at the speed of light.

Another big problem dealing with the speed of light is that the energy required rapidly and profoundly increases because mass increases as you get closer to the velocity of light speed. I think you mentioned earlier that it would require a VERY BIG spacecraft. I could be wrong, but I would think that a spacecraft even near the speed of light to begin to disintegrate with atoms of the craft separating or breaking down. As stated in one of the links below, "Our definitions of kinetic energy and momentum no longer work in the realm of special relativity." And even of that could be avoided, there's the problem of precise control. As also indicated, it would require some completely different physics.

That said, even if travel at or near the speed of light is impossible, that doesn't mean interstellar travel is impossible. Other ways are possible (though not proven) at slower speeds. A very large craft able to support multiple generations of people is one possibiity. It might also be possible to somehow use spacetime as a shortcut means to travel. Wormholes might also be possible shortcuts, although I think that's about as unlikely as traveling at the speed of light. Wormholes are hypothetical, and probably unstable to use for a variety of different reasons.

The only was I can imagine traveling at the speed of light is if the spacecraft can be broken down as information of evey atom and their placement and transmitted to a destination. Of course, that would also mean the need for a receiver on the other end which can reassemble that information back into a physical form.

Your thoughts on the views above will be appreciated.


Q & A: The Speed of Light | Starts With A Bang!

How Fast is the Speed of Light?

http://onlinephys.com/chapter123sci230.pdf
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Old 12-17-2011, 11:46 AM
 
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Remember, in space, you're at 0 G relative to earth's gravitational pull
Actually, in space you do experience Earth's gravitational pull depending on your distance from the planet. In low Earth orbit, you experience microgravity.
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Old 12-17-2011, 12:08 PM
 
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Originally Posted by orogenicman View Post
Actually, in space you do experience Earth's gravitational pull depending on your distance from the planet. In low Earth orbit, you experience microgravity.
Agreed. I'd take it a step farther by saying that gravity from all objects might not have any defined limit, but just gets progressively weaker with distance. Even if the combined gravitational forces from all objects is very weak, it could have an influence, one way or another, at very large scales. The gravitational attraction between the Earth and the Moon creates tidal effects.
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Old 12-17-2011, 08:42 PM
 
Location: US Empire, Pac NW
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Originally Posted by NightBazaar View Post
Yeah, as I said, there's LOTS of issues with interstellar travel.

You hit the nail on the head re: the energy it takes to accelerate as you start experiencing relativistic effects. As your mass increases, of course you need more energy to accelerate.

Newtonian and relativistic effects start to break apart when you get closer, but we can still approximate their effects for small accelerations (like 9.8 m/s^s). So I don't think there's any issues there ...

The bigger issue is how do you avoid stuff along the way? We don't have any way of predicting what's out there that we have to protect against. If its dust or micrometeors, we can deflect those with a shield in front of us made of a very strong material, like steel. Formed at an oblique angle to all sides (so shaped like a cone) I'm pretty sure we could simply deflect them. But that's empty weight to lug around while accelerating ... making the journey harder.

You are right in that anything we design would have to have at least one generation whose sole job is to upkeep the thing and likely will never see their destination.

That all assumes there isn't some way to travel in an interstellar fashion. I am somewhat heartened that in the middle of the 20th century, people thought supersonic flight was impossible. In fact there was a famous equation many thought would hold .. the incompressible fluid equation. But as it turns out, as soon as you get enough energy to go supersonic, it levels out more until you get going really fast, like re-entry fast (Mach 20).
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