Accelerating to a sizable % of C - Physical effects?

[hypersonic]

Just been pondering this..

Imagine we DID have some form of exotic propulsion that could help a ship attain a significant % of the speed of light, 20% - %50 or even greater.

If it COULD accelerate to a large % of light speed , what 'physical' limit might there be 'speed-wise' well before getting anywhere near light speed?

My thinking is around the assumption that if matter is accelerated towards C, it's density increases?, to the point that if you are at light speed, you'll be infinately dense???

Is this 'squashing' 'crushing' or whatever it is, a phenomonen that the ship 'would' actually experience, or is it one of those strange perception things... like time dilation. That 'locally' everything would 'seem' fine, but to an observer you'd appear 'denser'?

If it is the former, what 'speed' limit might have to be imposed upon a ship & it's crew before any 'noticable' effect on the perceived density started to have a detrimental effect. A bit like having a car that can go 150MPH, but a speed limit of 70mph is imposed for the sake of safety.

Or am i completely talking out of my Arse!?? LOL

Cheers
Al

 

[Urwumpe]

You have to remember the rocket equation.

For reaching the speed of light, you would need a massless thruster (no dry mass) emitting only light. This is of course impossible. So the mass fraction and the specific impulse define the top speed you can reach.

 

[Linguofreak]

Is this 'squashing' 'crushing' or whatever it is, a phenomonen that the ship 'would' actually experience, or is it one of those strange perception things... like time dilation. That 'locally' everything would 'seem' fine, but to an observer you'd appear 'denser'?

Time dilation, mass increase, length contraction, etc. are all effects that depend on reference frame. So those on board the ship wouldn't notice anything strange.

Safety considerations for near c travel would involve such things as radiation hazards and collision risks.

As you get closer to c, visible light gets blueshifted into the ultraviolet, and if you get going fast enough, eventually into the X-ray or even gamma range. Also, the only difference between a normal helium nucleus and an alpha particle, or a normal electron and a beta particle is how fast it's going, which means effectively that interstellar gas becomes ionizing radiation if you're moving at relativisic speeds. So between interstellar gas and the blueshifting of light, a spacecraft travelling at a significant fraction of c will have to deal with alot of radiation coming along its direction of motion.

As for collision danger, things can be bad before you even get to relativistic speeds. An object moving at 3 km/s has a kinetic energy equal to the yield of its weight in TNT, and kinetic energy goes up with the square of velocity at speeds much lower than c (in other words, twice as fast hurts four times as much, three times as fast hurts nine times as much). Once you start to approach c, kinetic energy starts going up much faster with velocity, and at 0.86c, the kinetic energy of an object is equivalent to the annihilation of its rest mass in a matter-antimatter reaction. In other words, a gram hitting at 0.86c yields 21 kilotons. 47 grams yields roughly a megaton. That's 8 or 9 US quarters, 9 or 10 British 20 pence coins, five pound sterling coins, 6 or 7 one Euro coins, 3 and a quarter tablespoons of water, or 6 tablespoons of flour. So hitting a pebble will have fatal results, not to mention blundering into the side of a comet.

 

[steph]

That might not be entirely true, although I might be wrong. Since the mass and density of the ship increase, shouldn't it be harder for radiation & objects to damage the ship?

 

[garyw]

That might not be entirely true, although I might be wrong. Since the mass and density of the ship increase, shouldn't it be harder for radiation & objects to damage the ship?

Mass increases with acceleration but not the tensile strength of the material.

In other words, just because your ship has more mass it doesn't mean the forward shields are any stronger.

Other problems with a sizeable percentage of C are navigation errors due to stellar abberation. Also, you can't use normal star trackers as the stars themselves have changes in the amount of light reaching the trackers.

 

[steph]

Other problems with a sizeable percentage of C are navigation errors due to stellar abberation. Also, you can't use normal star trackers as the stars themselves have changes in the amount of light reaching the trackers.

Indeed. I can hardly imagine a viable way of orientating during close to c travel. I guess, since it would be a direct flight anyway, that a course could be plotted, Millenium Falcon-style. But at such huge distances, a tenth of a degree off when you start the engines means you end up waaaay too far from your destination . Or that you end up in a star .

 

[garyw]

Indeed. I can hardly imagine a viable way of orientating during close to c travel. I guess, since it would be a direct flight anyway, that a course could be plotted, Millenium Falcon-style. But at such huge distances, a tenth of a degree off when you start the engines means you end up waaaay too far from your destination . Or that you end up in a star .

Oh, it's possible but you have to take those effects into account. You WILL need course corrections due to other gravitational influences.

And then there is the problem of data transmission - How do you transmit data to Earth? A simple transmission requires megawatts of power over those distances and the radio waves spread...............

 

[David]

Mass increases with acceleration but not the tensile strength of the material.

In other words, just because your ship has more mass it doesn't mean the forward shields are any stronger.

I question this. As the ship becomes more massive, the particles constituting it, become more massive, and therefore they would, to a greater extent, resist accelerative displacement by oncoming particles.

This raises another interesting consideration: as the particles become more massive, they would also, to a greater extent, resist the electrostatic forces that stabilize them, in positional reference to one another. The result could be a random tendency of the ship, to disintegrate.

It seems to me that there is some correlation, here. Any impacts by oncoming particles, are basically applications of electrostatic forces (since matter is mostly empty space). So, because of the increase in mass, collisions would tend to result, really, in a practical effect of the oncoming particles' passing through the ship, since the ship's particles would not be accelerated by the "collisions," and neither would the oncoming particles. I wonder if this implies a violation of conservation of momentum in collisions, or instead represents a reconsideration of whether there really are collisions.

(BTW, mass increases with velocity, not acceleration)

 

[Kaito]

My friend (who is a nerd, but a cool nerd) thought of a way to perceive the Speed of light: Like the sound barrier.

The problem was that the air would be pushing against the ship, and if it wasn't built right, it would blow apart. But, once we pass the sound barrier, supersonic flight becomes "easy" for the airframe to handle.

He thinks this same principle applies to the speed of light. It will be VERY hard to get there (like, the ships blowing apart), but once we pass it, it will be relatively easy for the frame to handle

 

[Linguofreak]

That might not be entirely true, although I might be wrong. Since the mass and density of the ship increase, shouldn't it be harder for radiation & objects to damage the ship?

The mass and density of the ship do not increase as seen in the ship's reference frame. It doesn't matter if we look at it as the ship travelling at 0.86 c and hitting the pebble, or the pebble travelling at 0.86 c and hitting the ship. The effects on the ship and the pebble are the same whichever way you look at it.


-----Posted Added-----

My friend (who is a nerd, but a cool nerd) thought of a way to perceive the Speed of light: Like the sound barrier.

The problem was that the air would be pushing against the ship, and if it wasn't built right, it would blow apart. But, once we pass the sound barrier, supersonic flight becomes "easy" for the airframe to handle.

He thinks this same principle applies to the speed of light. It will be VERY hard to get there (like, the ships blowing apart), but once we pass it, it will be relatively easy for the frame to handle

They are not at all the same. The sound barrier was a limit due to our incomplete understanding of how to design aircraft that could travel through air faster than sound and the fact that air does things at supersonic speeds that can be dangerous to a manned aircraft. And even though we didn't know how to build a man-carrying airplane that could *safely* exceed the speed of sound, gun bullets had been exceeding the speed of sound for centuries (since they didn't need to be able to carry a live human). So had the tips of bullwhips.

The "light barrier" is not a matter of dangers and difficulties. In empty space with nothing to collide with a spacecraft could get arbitrarily close to the speed of light with no ill effects. The "light barrier" is more a matter of the structure of space and time. For an object with a non-zero rest mass to reach the speed of light requires an infinite amount of energy (and thus infinite fuel). Also, exceeding the speed of light, even if you find some way to get around the energy barrier, always allows time travel, and since we do not see any time travellers appearing, it is a safe assumption that time travel is impossible.

So things like the sound barrier and some of the collision-related limitations we've been discussing on fast sublight travel are human limitations: limitations on how fast you can safely propel a human or a manmade object with a specific purpose. If there are no restrictions on safety, you can get things going very fast indeed. But the light barrier is a universal limitation: with sufficient technology you can get anything arbitrarily close to the speed of light safely. But *nothing*, regardless of purpose or safety, can travel faster than light. (There are a few special cases, but they have limited usefulness). It is a physical limitation hardwired into the universe.

 

[Kaito]

To answer the original question: I think the physical limit would be the ships strength, because as discussed before, the faster you travel, the more mass you have, and etc, etc, bang, you die.

To respond to the above:
Well, while the speed limit is "hardwired" into the universe, I believe that someday, we will find a way to exceed the light barrier, or find ways to bypass it. Such as the "warp drive": Expanding space behind you, and contracting it in front of you. I'm not physicist, so I'm not sure on the whole properties of this whole thing, but I'm just speculating here...:

What if we could generate perpetual energy, and use that energy to not only speed the ship up, but reduce its mass. So, the mass would remain "constant", but still speeding up. And by reducing its mass, i mean take energy out of the ship (because if E=MC², then M=E/C² (if i did my math right)). So, then technically, we could take mass away by taking energy away (and since you cant "Destroy" energy, it could be redirected to power the ship).

Thoughts/comments on the above?

 

[tblaxland]

What if we could generate perpetual energy, and use that energy to not only speed the ship up, but reduce its mass. So, the mass would remain "constant", but still speeding up. And by reducing its mass, i mean take energy out of the ship (because if E=MC², then M=E/C² (if i did my math right)). So, then technically, we could take mass away by taking energy away (and since you cant "Destroy" energy, it could be redirected to power the ship).

Thoughts/comments on the above?

You think developing perpetual energy would be any easier than accelerating to faster than light? Notwithstanding, even if you took all the mass of the spaceship except a minimalist payload and converted it into kinetic energy, the payload will still not be exceeding the speed of light. The payload's velocity will be determined simply by the payload mass fraction for your spaceship and hence could be arbitrarily close to the speed of light, but still not exceed it. You can do the math yourself if you like:
http://en.wikipedia.org/wiki/Kinetic_energy#Relativistic_kinetic_energy_of_rigid_bodies

 

[Kaito]

You think developing perpetual energy would be any easier than accelerating to faster than light? Notwithstanding, even if you took all the mass of the spaceship except a minimalist payload and converted it into kinetic energy, the payload will still not be exceeding the speed of light. The payload's velocity will be determined simply by the payload mass fraction for your spaceship and hence could be arbitrarily close to the speed of light, but still not exceed it. You can do the math yourself if you like:
http://en.wikipedia.org/wiki/Kinetic_energy#Relativistic_kinetic_energy_of_rigid_bodies

Math has never been my strong suit.
I was more looking at the theory of it, not reality of perpetual energy. O well, worth a shot. I'll leave this subject up to the real scientists

 

[TSPenguin]

Your suggestion would however allow us to freely travel the solar system with very little problems. Which is way cool!

 

[JamesG]

Finding a way to convert your ship to energy, "beaming" it to your destination, and then re-converting it back into mass (think StarTrek "transporter" concept taken to its most rediculous), is probably the only hypothetically "realistic" method for light-speed travel with the laws of physics as we know them. But accomplishing this technology is as plausable as building a rocket with enough omph to reach >3/4 c.

Flipping this thread around, literally.
How about attempting to decellerate relative to Earth or more importantly, in relation to the universe itself? Our concept and impression of time comes from our planet's motion thru the universe. If you could "slow down" would not time speed up for the observer (get a few more hours in the day)?

 

[tblaxland]

How about attempting to decellerate relative to Earth or more importantly, in relation to the universe itself? Our concept and impression of time comes from our planet's motion thru the universe. If you could "slow down" would not time speed up for the observer (get a few more hours in the day)?

Yes. See the Hafele–Keating experiment:
http://en.wikipedia.org/wiki/Hafele-Keating_experiment

 

[Linguofreak]

Finding a way to convert your ship to energy, "beaming" it to your destination, and then re-converting it back into mass (think StarTrek "transporter" concept taken to its most rediculous), is probably the only hypothetically "realistic" method for light-speed travel with the laws of physics as we know them. But accomplishing this technology is as plausable as building a rocket with enough omph to reach >3/4 c.

Flipping this thread around, literally.
How about attempting to decellerate relative to Earth or more importantly, in relation to the universe itself? Our concept and impression of time comes from our planet's motion thru the universe. If you could "slow down" would not time speed up for the observer (get a few more hours in the day)?

Well, The lowest speed you can get relative to the Earth is zero. To do that, you'd have to fly at the Earth's rotational velocity in the opposite direction. I believe at the equator this is roughly 1000 mph (or 500 m/s). You would gain some minuscule fraction of a second from relativistic effects, but it's so small as to not be worth calculating. But, since you wouldn't be moving with the Earth's surface as it spun, your "day" (in terms of how long it took the sun to rise, set, and rise again), would be a year long. (Since the Earth is moving around the sun, but you aren't moving around the Earth). The stars would not appear to move at all over the course of the year.

There's no real way to slow down relative to the universe itself, since it doesn't really have a velocity, but the closest you could get would be to find the velocity at which the cosmic microwave background is about the same temperature in all directions. I believe this corresponds to a velocity of abouit 600 km/s relative to the sun in a certain direction.

 

[steph]

We have yet to reach 0.01 of c, and we already think of ways to break c. Our current technology is mostly helpless when trying to reach accelerate big objects to close to c speeds.
Of course, in an ideal world, if most of the funds used for the army&such would go to scientific research, I guess it is reasonable to say that probes capable of maybe 1% of c using nuke pulse or antimatter propulsion, provided that a cheaper of producing it becomes available, could be constructed.

 

[jedidia]

To answer the original question: I think the physical limit would be the ships strength, because as discussed before, the faster you travel, the more mass you have, and etc, etc, bang, you die.

Physical Limit is NOT an issue. You're trying to break the speed of light without thinking in the lines of special relativity.

For a start, the basics of special relativity is summarized in one sentence: "The physical properties in any stable frame of reference are the same".

Stable frame of reference means a frame that does neither accelerate nor decelerate. Physical limits of a ship would only answer to the question of how fast you could accelerate, not of how fast you can be going.

Take the nice old question: "Is the train moving or is it the station?"

When you have a stable frame of reference (i.e. moving at constant speed) The answer lies solely in the eye of the beholder. If you put a train station into space and let your ship fly by, no matter at which velocity, the one will not experience more strain than the other. And if there are no other objects around, there is no telling wheather the train moves or the station.
When sitting inside a spaceship, there is no telling weather you move through the universe or the universe passes you by. There is NO difference whatsoever... as long you're not aplying energy, i.e. accelerating or decelerating (which is, from a relativistic point of view, exactly the same, since there is no absolute frame for comparison).

When locked into a cell without connection to the outside in a ship that moves at 99% C, there would be no way you could tell that the ship is moving at all!

For a practical example, fire up Orbiter, plot a course to mercury, analyze your trajectory and then try to answer the question: Am I Catching up to mercury... or is mercury catching up to me?

 

[Nexiss]

just a thought, what about slipstring drive theory?