Relativistic Travel.

[daniel l.]

Now, I'm not a very knowledgeable person in terms of physics. but I know that time slows down for you when travelling at speeds close to lightspeed. and the effect gets stronger the closer you get to 1c, this means, that you could cross entire galaxies in a matter of so little as seconds depending on your velocity (This can vary, Anything from the natural amount of time that it would take, to a nearly instantaneous jump. It all depends on how close to the speed of light you are.). Of course, time would continue normally outside of your ship so you'd find upon arrival that thousands of years have passed. But for a crew that had nothing left to lose, or a civilization that has achieved immortality, then it could be an easy method of travel.

what do you guys think? Would it work? Would it be a workable system?

[monophonic]

As far as physics is concerned, yes. The rest is "just" engineering. And the energies required are so ridiculously high they would be thrown out from any sci-fi show as absolutely unbelievable. So, to summarize: no.

[DoctorDavinci]

I'll just leave this here ... 

 

[Bornholio]

One well known piece of matter has been detected with the "seconds' to cross the galaxy.  A proton hit the upper atmosphere and was detected by the Chicago air shower array called the "oh my god particle". https://en.wikipedia.org/wiki/Oh-My-God_particle

Its energy was equivalent to a 94mph fastball. In one proton.  Your calculator does not have enough digits to display the number of 9's behind .9c at the time there was no known emitter within the range needed (at that speed the background microwaves slow you down like water on a ship hull). It lead directly to discovering that the center of our galaxy hid a super-massive black hole. Its estimated that it needed to ride several explosive shock-waves generated by the black hole.  A proton has 938MeV or 9.4x10^12, this proton had 3x10^20eV in kinetic energy and exploded into a cone of millions of secondary particles like muons and electrons.

All this demonstrates the extreme top end of RE. at a significant fraction of light speed you posses more kinetic energy than mass energy.  Your interaction with matter moving at normal speeds is more energetic and lethal than a spray of antimatter. And it gets worse as your speed goes up.  At speeds needed to be useful for time dilation stray electrons and protons in the solar wind would gamma-ray cook your ship as you come in contact.  Avoiding this would require diverting them and be a huge drag force.

Also imagine Saturn rockets except instead of Kerosene and Oxygen, fueled with antimatter and matter.  They still don't get you to that "really useful" range of dilation.  The Enterprise can't possibly carry enough antimatter to get to 0.5c never mind meaningful dilation.

Edited March 23, 2017 by Bornholio
clarify, link

[p1t1o]

I just read a book by Alastair Reynolds called "The House of Suns" in which a faction of humanity spends its time circumnavigating the galaxy at high relativistic speeds, exploring and meeting once per circuit.

They have been around for approx 6 million years due to time dilation, most of them alive the whole time. Whilst the rest of humanity is engaged in what is called "turnover", in that empires and civilisations rise and fall, worlds move from high tech golden-age civilisations and fall back to stone age conditions and rise back up again in generally predictable cycles.

Good book, recommended. Also the rest of his books.

***

Also there is a well-known thought experiment that delineates how if you were to somehow build a ship that can accelerate at 1G continuously forever (the thought experiment does away with worrying how) time dilation would get so extreme that you could cross the entire observable universe in as little as a century of ship-time.

Edited March 23, 2017 by p1t1o

[Shpaget]

Once you get to five or six nines, you'd be facing quite a bit of gamma radiation from all the blueshifted starlight. Come close (astronomically speaking) to a star, and you're zapped.

No worries, though. Dust particles will nuke you long before that.

[StrandedonEarth]

10 hours ago, p1t1o said:

I just read a book by Alastair Reynolds called "The House of Suns" in which a faction of humanity spends its time circumnavigating the galaxy at high relativistic speeds, exploring and meeting once per circuit.

Thanks for the suggestion, I just put it on hold at the library. Only one copy in the entire system, and it's on a shelf 30 miles away...

[YNM]

Two problems :

1. Propulsion. "Tyrrany of rocket equation" comes to mind.

2. Right of way. Sector ZZ9 Plural Z Alpha and all the other sectors are not clear for this.

[0111narwhalz]

RE: Rocket Equation

Staged beam-core AM? Tsiolkovsky only counts for single stages. Since the engine itself is so heavy, and makes so little thrust anyway, you could probably just use drop tanks.

Edited March 24, 2017 by 0111narwhalz

[YNM]

1 hour ago, 0111narwhalz said:

RE: Rocket Equation

Staged beam-core AM? Tsiolkovsky only counts for single stages. Since the engine itself is so heavy, and makes so little thrust anyway, you could probably just use drop tanks.

The point is, accelerating things to 0.9999....something (still real and different than 1) c takes an insanely huge amount of energy. Look up the oh-my-god particle - can you imagine a mote of dust, even to dust of dusts itself, holds energy as much as a pitched baseball ?

Edited March 24, 2017 by YNM

[p1t1o]

14 hours ago, Shpaget said:

Once you get to five or six nines, you'd be facing quite a bit of gamma radiation from all the blueshifted starlight. Come close (astronomically speaking) to a star, and you're zapped.

No worries, though. Dust particles will nuke you long before that.

Thats why you build your ship inside 60 gigatons of ice

What do you mean "heavy"?

 

[FleshJeb]

It's a science fiction staple:

https://en.wikipedia.org/wiki/Tau_Zero

https://en.wikipedia.org/wiki/A_World_Out_of_Time

[wumpus]

1 hour ago, FleshJeb said:

It's a science fiction staple:

https://en.wikipedia.org/wiki/Tau_Zero

https://en.wikipedia.org/wiki/A_World_Out_of_Time

I was thinking "Forever War", but these appear to precede it.  The really hard parts are infinite Isp (presumably using antimatter) and "navigation shields" to avoid the high energy bombardment mentioned above in the thread.  Things should get going after about a year of accelerating at one g (basically giving you roughly the momentum of m_restc(=m_effectivev).

 

[Shpaget]

22 hours ago, p1t1o said:

Thats why you build your ship inside 60 gigatons of ice

What do you mean "heavy"?

 

Hmmm, I wonder how long it would last.

Let's go and do the math! I'm doing the calculation and googlinglive as I type, so I don't know what result will I get.

First, let's figure out the kinetic energy of a typical micro particle found in the interplanetary space. They are usually under 100 micrometers, so, let's take 50 um. The volume of sphere of that diameter is 6.545x10^-14 m^3, with the average M class asteroid density of around 5 g/cm^3, that brings us to the mass of 3,27x10^-7 kg.

So, the kinetic energy of that particle at 0,999999c would be 2,07x10^13 J, which is roughly equivalent to a 5 kt nuke, which is a modest sized tactical nuke.

Now, let's see how often would our spacecraft be struck by such particle. I'm having trouble finding the data on the frequency of such particles in space but I did find the estimate that Earth is struck by 37,000-78,000 tons of the stuff each year. Let's take the low number of 40 000 tons, or 40 000 000 kg per year. There would be roughly 120 000 000 000 000 particles that hit the Earth in such a scenario. If we take our spaceship to have a rather tiny cross section of just 200 m^2, that means, our ship would be struck around 180 times in one Earth orbit, which it would cover in just under an hour.

This article

https://www.quora.com/What-is-the-size-of-a-crater-left-by-the-average-thermonuclear-bomb

states that a 104 kt (subterranean) bomb excavated 11 000 000 tons of material, so our 20 times smaller bomb would dig up 500 000 tons. To reach our 60 gigatons mark, we would need 120 000 strikes, which would occur in roughly 25 days.

Shield not heavy enough.

Edited March 25, 2017 by Shpaget

[daniel l.]

9 minutes ago, Shpaget said:

Hmmm, I wonder how long it would last.

Let's go and do the math! I'm doing the calculation and googlinglive as I type, so I don't know what result will I get.

First, let's figure out the kinetic energy of a typical micro particle found in the interplanetary space. They are usually under 100 micrometers, so, let's take 50 um. The volume of sphere of that diameter is 6.545x10^-14 m^3, with the average M class asteroid density of around 5 g/cm^3, that brings us to the mass of 3,27x10^-7 kg.

So, the kinetic energy of that particle at 0,999999c would be 2,07x10^13 J, which is roughly equivalent to a 5 kt nuke, which is a modest sized tactical nuke.

Now, let's see how often would our spacecraft be struck by such particle. I'm having trouble finding the data on the frequency of such particles in space but I did find the estimate that Earth is struck by 37,000-78,000 tons of the stuff each year. Let's take the low number of 40 000 tons, or 40 000 000 kg per year. There would be roughly 120 000 000 000 000 particles that hit the Earth in such a scenario. If we take our spaceship to have a rather tiny cross section of just 200 m^2, that means, our ship would be struck around 180 times in one Earth orbit, which it would cover in just under an hour.

This article

https://www.quora.com/What-is-the-size-of-a-crater-left-by-the-average-thermonuclear-bomb

states that a 104 kt (subterranean) bomb excavated 11 000 000 tons of material, so our 20 times smaller bomb would dig up 500 000 tons. To reach our 60 gigatons mark, we would need 120 000 strikes, which would occur in roughly 25 days.

Shield not heavy enough.

Electromagnetic deflectors could work. Or perhaps lasers? If you had the power for achieving such velocities, you might be able to make a terawatt laser that fires in the forward path of your ship, due to the high velocity of ship vs laser, I can imagine that the laser would end up compressing itself into a dense buffer zone that would incinerate anything that got close.

[Shpaget]

That would only add the energy of the laser to the energy of the particle. Double the trouble.

[daniel l.]

2 minutes ago, Shpaget said:

That would only add the energy of the laser to the energy of the particle. Double the trouble.

If you're firing against the motion in which the particle is moving? Wouldn't that decelerate it?

[Shpaget]

Perhaps, but you only trade kinetic energy for thermal. Total is the same.

[daniel l.]

35 minutes ago, Shpaget said:

Perhaps, but you only trade kinetic energy for thermal. Total is the same.

But if the majority of space particles are no bigger than a sand grain, then should a powerful concentrated light buffer not vaporize it instantly?

[RCgothic]

At those speeds the difference between hitting a solid and a gas is negligible. Might help if there's time enough for the generated gas to diffuse out of the path, but see again the ridiculously fast speeds involved.

[daniel l.]

4 minutes ago, RCgothic said:

At those speeds the difference between hitting a solid and a gas is negligible. Might help if there's time enough for the generated gas to diffuse out of the path, but see again the ridiculously fast speeds involved.

Would it be easier to diffuse a gas with an electromagnetic field?

[Green Baron]

A sandgrain (SiO2 silt) of 0.1mg (10^⁻7kg) hit at 0.8c (240,000,000m/s) (where relativity doesn't count that much yet) has a kinetic energy of 0.0000005 * 240,000,000² = 28800000000J or 28.8GJ (maybe someone check this). That is roughly 7 metric tons of TNT exploding on impact on the hull. We know what a few tens of grams of explosive do to an airliner hull.

Yes, a star trek reflector shield and correctly calibrated dilicium crystals would solve the problem :-)

Also, as you reach c, you literally run out of space (which is compressed in direction of travel) and time. You cannot look forward because there is no "in front of", and there is no reaction time. The dust particle on the other side literally has all the time of the universe.

Until ~0.8c you might be fine with the classic "view of things", though no known energy source could accelerate a massive object like a ship to that speed. "Breakthrough Star Shot" is far from 0.8c yet their proposed laser parks are just dreams as are their "ships" of a few gram.

EM-fields: does dust fly from a transmitting antenna ? Ok, alien ships explode if exposed to loud music :-)

 

Search: kinetic energy, electromagnetism, this forum (!), general relativity, relativistic mass, time dilation. Many of your questions can be answered when browsing through physics forums ...

 

 

Edited March 25, 2017 by Green Baron
, and .

[kerbiloid]

Moving at 0.99... c it's not enough to vapourize the dust, you must accelerate it away from your path.
Shooting it from 3000 km, you have 3000 / 300 000 = 0.01 s until you reach the plasma cloud. So, the vapourized atoms will pass just several meters aside.

You should either shoot them from millions km to let the plasma cloud dissipate itself, or push the atoms with the laser radiation in fron of your ship until they get off your way,
Anyway you need a megalaser accelerating atoms before you.

And the faster you move - the smaller particles are dangerous, the more powerful front laser you need.
Or magnetic shield - absolutely no difference. Anyway, an electromagnetic emitter pushing the dust forward.

So, while one torch throws atoms back pushing your ship forward, another one pushes atoms forward sending your ship back.
The greater is velocity - the lesser is their thrust difference.

Reaching some velocity depending on the dust cloud density you will just spend your engine thrust to withdraw your front torch thrust.
If you switch off your engine, you still need your front flamethrower, and it will be braking down your speed.
On other hand, you can say you are braking down by intension.

So # 1.
Your physically possible speed is limited by the interstellar atoms density on your route and probably _{need to calc} is much, much lesser than those famous "nines after period".

So # 2.
If you are going to use an interstellar rocketship, you must have two similar engines or torches: front and rear.
On start you begin using the rear one to accelerate.
Once your speed gets enough high to be afraid, you switch on the front one and begin to kill'em all with fire, increasing the front torch power parsec by parsec.
Reaching some midpoint, you have two torches pushing the ship with the same force, i.e. get zero thrust, and can no more accelerate.
You shut down the rear engine and continue decelerating with the front one which is also your flamethrower, decreasing the front torch power parsec by parsec.
You arrive to your destination with zero speed and shutdown the front torch.

So, matching your acceleration with a desired distance, you vary the flight range (as you must hold the front torch fired all the way).

As you don't want to push two superengines against the botton of each other, in fact your need a big toroidal ship with bidirectional plasma flow.
Then you don't have two engines to be switched on/off, but just redistribute your bidirectional torch radiation.
Also then you can use the engine magnetic field to suck the surrounding gas from safe directions and to use it as reactive mass.

P.S.
I'm now thinking, where are other siblings of the oh-my-god-proton. Any dust particle had zillions of them.
 

Edited March 26, 2017 by kerbiloid

[Green Baron]

Spaceballs's Mega Maid comes to my mind :-)

Nope, needs a ludicrous long cable.

[p1t1o]

On 3/25/2017 at 7:45 AM, Shpaget said:

Hmmm, I wonder how long it would last.

Let's go and do the math! I'm doing the calculation and googlinglive as I type, so I don't know what result will I get.

First, let's figure out the kinetic energy of a typical micro particle found in the interplanetary space. They are usually under 100 micrometers, so, let's take 50 um. The volume of sphere of that diameter is 6.545x10^-14 m^3, with the average M class asteroid density of around 5 g/cm^3, that brings us to the mass of 3,27x10^-7 kg.

So, the kinetic energy of that particle at 0,999999c would be 2,07x10^13 J, which is roughly equivalent to a 5 kt nuke, which is a modest sized tactical nuke.

Now, let's see how often would our spacecraft be struck by such particle. I'm having trouble finding the data on the frequency of such particles in space but I did find the estimate that Earth is struck by 37,000-78,000 tons of the stuff each year. Let's take the low number of 40 000 tons, or 40 000 000 kg per year. There would be roughly 120 000 000 000 000 particles that hit the Earth in such a scenario. If we take our spaceship to have a rather tiny cross section of just 200 m^2, that means, our ship would be struck around 180 times in one Earth orbit, which it would cover in just under an hour.

This article

https://www.quora.com/What-is-the-size-of-a-crater-left-by-the-average-thermonuclear-bomb

states that a 104 kt (subterranean) bomb excavated 11 000 000 tons of material, so our 20 times smaller bomb would dig up 500 000 tons. To reach our 60 gigatons mark, we would need 120 000 strikes, which would occur in roughly 25 days.

Shield not heavy enough.

Not for nothing, but you chose a *very* high relativistic speed there, knock 30km/s off your speed (so two 9's less) and the kinetic energy of incoming particles drops by a factor of 10.

Though I couldnt find much in the way of densities, it was clear that one can expect the solar system to be an area of increased density.

I would also wager that there is a better approximation than comparing it to subterranean nukes - the energy is not going to be released at depth but quite close to the striking surface.

But even so, under some conditions it still might not be enough

For the Daedalus designs, albeit considering a much lower relativistic speed, used boron as a shield due to its high heat of vaporisation.

Either way, if you are going to put that many 9's in your relativistic speedometer, you are going to need a very heavy shield indeed, or some other way of dealing with it.

Edited March 27, 2017 by p1t1o