How far could a spaceship go if we never ran out of thrust? (2020)

https://www.forbes.com/sites/startswithabang/2021/12/30/how-far-could-a-spaceship-go-if-we-never-ran-out-of-thrust/

by ec109685 • 5 years ago

280 331 5 years ago

adrianN2• 5 years ago

The social effects of relativistic time dilation are an important topic in "The Forever War".

Fantastic sci-fi novel with continuing modern relevance. Often interpreted as metaphor for the author's experience in the Vietnam War, and his return to American society after what felt like a period of otherworldy time-dilation.

The graphic novel version is great too, if you can find a copy:

https://en.wikipedia.org/wiki/The_Forever_War_(comics)

quickthrower23• 5 years ago

I never knew you could get that far in that amount of time (experienced by passengers) with just 1g of force so it’s thoroughly interesting and in some sense everything is quite close: as long as you are OK with a one way ticket.

londons_explore2• 5 years ago

A one way ticket with no messages back to/from home.

mattowen_uk• 5 years ago

For such a long trip, the only logical ship type would be a self-sustaining generational colony ship full of hundreds of people. The concept of 'home' would quickly shift from being the Earth to being your ship, so staying in contact with your origin planet would become irrelevant.

senectus1• 5 years ago

after the last year I imagine quite a few people would put their hand up for that.

but also, what about deceleration?

You gotta stop some time to smell the roses... so would you cut that acceleration time in half to decelerate?

CodeGlitch2• 5 years ago

Also why stop at 1g? People could be trained to live in 1.2 or even 1.5g.

simiones2• 5 years ago

It's important to note though that this kind of ship is still impossible as far as I remember - even with matter/antimatter reactions (which theoretically gives you E = mc^2 energy, the maximum possible per kg), you can't get enough energy to accelerate to the mass of the fuel to 1g, nevermind the rest of the ship, for the duration required for interstellar travel.

grey413• 5 years ago

The amount of energy required for fast interstellar travel is mind-boggling. People do not comprehend the scale. Even with ridiculous things like massless fuel it would take multiple times the entire yearly energy expenditure of the earth for an ISS sized ship to travel 10 light years before the passengers died of old age.

rbanffy2• 5 years ago

Interesting to note that when you are travelling close to c, even intergalactic vacuum requires a lot of mass ahead of you so the ship is not vaporised.

Remember that when you are travelling to that galaxy 18 billion light years away, you’ll hit every photon it sent our way over 18 billion years in just about 45 years.

bobsmooth• 5 years ago

I always knew intergalactic hydrogen might be a problem but I never considered the effect of travelling really fast on photon absorption.

dvdkhlng• 5 years ago

If you travel close to C, those photons will be blue-shifted into (depending on velocity) very energetic photons (x-ray, gamma spectrum) that may be rather difficult to shield against.

rbanffy2• 5 years ago

The hydrogen may be a problem well before the light or CBR become another.

jsilence3• 5 years ago

Nah, just put a solar panel at the front of the ship. Free energy!!

nindalf• 5 years ago

And use that energy to sustain the acceleration. Sounds like a perpetual motion machine!

wcoenen• 5 years ago

Even ignoring galaxies, there's also the cosmic microwave background.

It turns out that there is a rest frame in which this background looks the same in all directions. But if you keep accelerating in one direction, the CMB coming from there will keep blueshifting: from microwave to IR, to visible, and eventually hard gamma radiation.

eru6• 5 years ago

It turns out that there is a rest frame in which this background looks the same in all directions.

I was really surprised when I heard this for the first time a while ago. Because it means that our universe does have a _preferred_ frame.

nabla9• 5 years ago

CMB rest frame is important and special unique frame to use as a reference.

Relativity means that there are no special frames where the laws of physics are different.

remcob• 5 years ago

Could that radiative energy be turned into propulsion, at least theoretically?

marcyb5st5• 5 years ago

Yes, but photons carry momentum even if they are massless, and you can't convert more than 100% of that momentum to energy for propulsion. So, if you achieve perfect efficiency, you can avoid them from slowing you down and still have to rely on internal energy sources to accelerate you .

littlestymaar3• 5 years ago

It's even worse than this:

- all those photons are blue-shifted and becomes hard gamma rays.

- once you get close enough from c, all the stars in the universe appear to be either right in front of you, or right behind you, which means you get hit not only by gamma photons coming from the galaxy you're aiming at, but gamma photons coming from half the universe!

rakoo• 5 years ago

once you get close enough from c, all the stars in the universe appear to be either right in front of you, or right behind you,

I don't understand that one, could you please expand on how it works ?

hinkley4• 5 years ago

I think this is why the Alcubierre drive will become critical even at well below light speed. Assuming I understand the physics correctly, the bubble of space around the ship is not moving (very fast) relative to the ship and so moving at fractional c will see an increase in flux but not the blue shift. You’re still hitting every spec of dust in your path, but not turn the entire cone of the universe in front of you into gamma rays.

At some point the warp drive might be cheaper than the shielding.

IX-103• 5 years ago

  once you get close enough from c, all the stars in the universe appear to be either right in front of you, or right behind you

That's not really right. There is a distortion where things appear more in front of you than they are at the time you see them, but that's only because they were at that angle, but by the time the light gets to you they're not where they appear.

Also there's nothing that would shift light to appear behind you other than your movement away from objects that you have passed.

MichaelZuo• 5 years ago

Yes, shielding would be even more difficult at those speeds than ‘unlimited thrust’.

xwdv• 5 years ago

If you happened to be a civilization that lived at the very edge of the universe, such that every star was in one direction and there was only black emptiness in the other, could you the accelerate indefinitely into the blackness without worrying about having mass to shield you?

taneq3• 5 years ago

This reminds me of the Lighthuggers in Alastair Reynolds' Revelation Space novels. They're powered by handwavey 'Coinjoiner drives' that sidestep the question of reaction mass or power sources, and so are able to accelerate to very close to the speed of light (hence the name). They have a few interesting features:

1) Uniquely (to my knowledge for starships in hard-ish scifi) they're are 'aerodynamically' shaped, or at least long and pointy to minimize friction with interstellar mass.

2) Their front surfaces are covered in a thick layer of water ice which acts as an ablative shield against said mass and radiation.

3) The fact that they can accelerate at over 1G means that they can land tail-first on an Earth-type planet.

londons_explore2• 5 years ago

Say you take the one-way ticket to travel to a far off galaxy at 1g acceleration to go mine space-diamonds...

What when someone else in a few hundred earth years invents the 1.1g rocket to go mine those same space diamonds? They will arrive millions of (local) years before you. By the time you arrive, the space diamonds will be all mined and you'll be seen as a cave man.

That reason alone means it's never worth departing on a long journey, because someone else always has an incentive to overtake you and get there millions of years sooner.

adrianN2• 5 years ago

Aha, but if everyone thinks that way you will actually be the only one daring enough to embark on that journey and have all the space diamonds for yourself!

ehnto• 5 years ago

By that reasoning, no-one ever leaves. If no-one had ever left, you may as well have left and be there already.

I think the reason to leave will have to be something other than space-diamonds, or other monetary needs. More like planetary conquest and scientific advancement.

jusssi• 5 years ago

In addition, something approacing from opposite direction might already be there when you decide to launch, digging away at the diamonds. Or a local star might have gone nova and vaporized the whole diamond field.

RavlaAlvar• 5 years ago

Or someone who invented a device that can fold space time.

vidarh• 5 years ago

Quite a few scifi stories have explored the idea of someone leapfrogged that way. I think it'd be a major concern of sending someone that way.

[For one light take on this, the original Marvel "Guardians of the Galaxy" (the year 3000 versions) have Vance Astro, Major Victory, go on a 1000 year journey to Alpha Centauri, only to find other humans got there centuries earlier and were waiting for his arrival]

est313• 5 years ago

Currently we are in a phase of rapid scientific progress, but there is no law that this will continue forever. One day we'll hit diminishing returns and instead of discovering new things, science will be about applying the knowledge discovered in the past correctly, as well as not losing it. Thankfully we are still far away from this.

withinboredom• 5 years ago

Not only that, but whatever star the space diamonds are orbiting probably won’t be there any more.

mewpmewp2• 5 years ago

It would be quite a fun expedition though, knowing that when you reach your destination there could already be many others who have reached that point so you can see how everything has advanced. Assuming your goals are oriented more towards curiosity rather than making money.

You sacrifice 30 years to see what someone potentially achieved within 1 million years. I'm sure there would be people willing to do that.

Let's say I'm an uber billionaire (trillionaire in the future), aged 45, I might think that I have tried already everything there's to try on earth and want to see the future. I would build a ship with more than enough entertainment for following 30 years and invite bunch of other people and just start with the journey.

Maybe I could even leave some money behind for other groups to keep building better solutions that would reach the destination much sooner so they can already start building out the destination and have millions of years of time to do that before I reach there.

It would be an enormous risk of course, but it could also pay off very well if for example you still own a large proportion of the business you leave behind to build the following spaceships and if it ever should reach the destination was still legally upholding the ownership you have. In fact in this case you could be magnitudes more richer in the new location when you arrive as compared to when you left 30 years ago in your time.

Or if something like cryogenic freeze is possible, you could also do that for some of the years if you ever got bored in the ship.

neartheplain2• 5 years ago

That's also a common Star Trek plot point. Many episodes involve the Enterprise catching up to a ship launched from Earth in the pre-warp era, typically an early colony or exploration vessel. The most of famous of these might be Khan Noonien Singh's "Botany Bay:"

https://memory-alpha.fandom.com/wiki/SS_Botany_Bay

topynate• 5 years ago

They will arrive millions of (local) years before you.

No they won't – in the frame of reference of the galaxy, both you and your pursuer will spend most of the journey traveling at very close to the speed of light. The difference won't be enough to catch up.

Put another way, in the frame of reference of the galaxy, you get to Andromeda (2.5 million light-years away) only about two years later than light would. Your pursuer, traveling at 1.1 g, would get there about a year and 9 months after light. So anyone chasing you would have to take off within about three months – and after a year, nothing could catch you.

This arrival time delay relative to light is pretty much constant (for fixed g) for any distance over about 1000 light years. For this reason, sci-fi authors who want ships to be overtaken by later models either slow the old ships down to much less than light-speed (i.e. generation ships) or introduce FTL travel.

sudhirj• 5 years ago

The implications of time dilation when moving near c are also explored in the Three Body Problem trilogy, and pushed to the extreme as well. It’s quite a mindfuck if you still have ties to the place you’re leaving, but interesting if you don’t.

There’s all the interesting idea of just accelerating forever, till the end of the universe (which comes faster than you think if you’re going that fast).

simonh4• 5 years ago

We're really spoiled by modern rapid global travel. In the 1930s half of my maternal grandmother's family emigrated to New Zealand. I've only ever met two of those relatives once in the 1990s, but before jet travel such contact was impractical for most people. That's why whole family groups, or even communities would move together.

edna3145• 5 years ago

The time dilation aspect in space travel is the most neglected in popular sci-fi. In many of these, there are intricate installations of some sort cryogenic sleep devices because the script authors assume that it takes you 150 years of travel at light speed to get to a place that is 150 light years away.

CodeGlitch2• 5 years ago

Interstellar explores this idea really well. Also see Andy Wiers' new book "Hail Mary", which I can thoroughly recommend. In Hail Mary he doesn't use cryogenics but a different mechanism.

nahuel0x• 5 years ago

Interstellar merged relativity effects with emotional ones, that's a brilliant literary stroke analogous to the ones from the s.f. masters.

eesmith6• 5 years ago

... what? It's been part of SF for decades.

The first three that come to mind are: Heinlein's "Time for the Stars", Haldeman's "The Forever War", and Anderson's "Tau Zero".

From those titles, a DDG search finds http://sf-encyclopedia.com/entry/relativity listing more, also containing the line "Very many sf stories use relativistic time dilation for one-way Time Travel into the future."

edna3145• 5 years ago

I'm sure it has been, but I'm mainly talking about popular sci-fi movies. I'm sure you have at least one in mind where they have these 'sleep' devices.

akvadrako3• 5 years ago

There are very few sci-fi movies or books where relativity is important and they treat it seriously. Tau Zero is one, I'm not sure about Time for the Stars, but Forever War does have FTL.

I created a list of all these works I could find a few years ago. Here is one link:

https://tvtropes.org/pmwiki/discussion.php?id=l6q90mvssgscsj...

I think this is a complete list of the films and tv series:

  - The Star Lost
  - Pandorum
  - Passengers (2016)

simonh4• 5 years ago

That's a very basic error, but I can't offhand remember coming across a story where the author made this mistake. After all, if the ship's top speed is even modestly below light speed the journey really could take many decades. Can you give an example?

edna3145• 5 years ago

I wasn't referring to the author in the article, but rather an unspecified collection of 'popular' SciFi, where this aspect is not explained. It is true that, even if you reach speeds of 0.5c you only get a ~15% time dilation.

jobigoud• 5 years ago

the script authors assume that it takes you 150 years of travel at light speed to get to a place that is 150 light years away

Or maybe they know you wouldn't travel at light speed in the first place.

air7• 5 years ago

"In fact, so long as you kept adhering to this plan, you could choose any destination at all that’s presently within 18 billion light-years of us, and reach it after merely 45 years, max, had passed. That ~18 billion light-year figure is the limit of the reachable Universe, set by the expansion of the Universe and the effects of dark energy. Everything beyond that point is currently unreachable with our present understanding of physics"

What happens if I just keep going?

hoseja• 5 years ago

Notice the "presently".

Lariscus• 5 years ago

You would never reach your destination and at some point you would be stranded in dark space. This kurzgesagt video has some info on this topic.[1]

[1] <https://www.youtube.com/watch?v=uzkD5SeuwzM>

stouset2• 5 years ago

I don’t quite understand this. I think I’d maybe understand if space dilated to the point where you couldn’t quite hit that edge. Though now that I say it that “solution” seems to come with a whole bunch of problematic consequences.

But “not getting to anything past the furthest thing we can see from earth today” seems fundamentally incompatible with the idea of reaching those farthest points in a reasonably bounded timeframe. There is stuff beyond the limits we can see, it’s just further than light has had a chance to travel so far (and may ever travel).

My intuition is that as you approached those far objects, you’d observe them rapidly evolving forward in time until they reached their “present day” situation, able to see billions in light years in all directions with Earth right at the edge.

But then what happens when you look at Earth? Surely you don’t see it’s billions of years old past. You’d have to see it at least as old as it was when you left. But something doesn’t seem quite right about that to me. Surely I’m missing something.

gambiting• 5 years ago

As far as I understand - you'll come back to where you started.

simonh4• 5 years ago

I'm afraid not, the accelerating expansion of the universe will stretch out space ahead of you faster than you can traverse it. From your perspective the galaxies will become sparser and sparser over time until you're in an ever colder eternal black void.

DarkWiiPlayer• 5 years ago

The way I understand it is that it's not impossible to cover the distance, but that by the time you do, the distance between your starting point and your destination will have (at least) doubled due to the expansion of space.

So you're still as far away from your destination as in the beginning (or even further), but now you're the same distance from your starting position as well and are effectively stranded.

perihelions• 5 years ago

Well, an accelerating mass emits gravitational waves; and your spaceship is asymptotically infinite-mass; so at some point you destroy the universe. (Or at least the parts that are causally connected to you -- I guess cosmic expansion would save parts of it?)

I don't know whether you observe this or not.

Gunax• 5 years ago

There is a misconception that expanding space prevents us from ever reaching a destination. It's counter-intuitive (https://en.wikipedia.org/wiki/Ant_on_a_rubber_rope) but falls out of the math. If space expands at a constant rate, you could eventually reach any destination at any velocity.

But if the expansion of space is accelerating (which we believe currently), this is not true. There really would be destinations that are unreachable.

You would continue to travel further from your origin, but also witness your destination accelerate away.

stavros11• 5 years ago

But what if you accelerate faster than it does?

secondcoming• 5 years ago

Can scientists count the number of far distant stars that are no longer visible due to space accelerating?

philiplu• 5 years ago

For a hard science fictional version of this, check out Poul Anderson’s “Tau Zero”, from 1970, according to Wikipedia. I read it a few years after that, and it’s stuck with me since. A ship with a Bussard ramjet runs into troubles and has to keep accelerating, into the far future.

eesmith6• 5 years ago

Those interested in this topic may also like the extensive background materials and guidelines at Project Rho, eg, http://www.projectrho.com/public_html/rocket/slowerlight3.ph... .

bencollier49• 5 years ago

"spacecrafts" - urgh! Who wrote this?

jillesvangurp• 5 years ago

Relativistic speeds are a plot point in Andy Weir's recent book "The Hail Mary Project". You might know him from the Martian a few years ago.

Scott Manly did a Youtube episode on all sorts of weird propulsion mechanisms that people have come up with over the years a few months ago: https://www.youtube.com/watch?v=QEZv_OXA_NI. There are some interesting concepts in there. Including the anti matter based concept discussed in the article. Particularly fusion looks like it might get us some interesting amounts of delta v.

JoachimS• 5 years ago

Relativistic speeds are a plot point in Andy Weir's recent book "The Hail Mary Project". You might know him from the Martian a few years ago.

Just read the book and can highly recommend it. One of the good thing about it is that the main protagonists are nice, curious and friendly. No backstabbing, suprise turns of evilness to create suspense. A pleasant read.

vagrantJin5• 5 years ago

Can confirm, it is a really good read. I especially liked that the protagonist really does things a normal person would do despite the extraordinary circumstances. I wish hollywood could take notes.

stavros11• 5 years ago

No backstabbing, suprise turns of evilness to create suspense.

Spoiler alert, kind of.

pomian2• 5 years ago

All of Andy Weir's books are really good. There is even a surprising one that's fun. Also recommend Saturn Run, by John Sandford, while we are on this topic.

philipswood2• 5 years ago

Tau Zero by Poul Anderson also has a plot built around time dilation.

Koshkin4• 5 years ago

Sure, with the comfortable acceleration of g during the first half of the journey and decelerating during the rest of it, I could arrive to, say, Andromeda galaxy in a few dozen years. The biggest question, though, for me is: OK, I’m here, now what? (Having a vivid imagination, as a child I once imagined myself standing on the Moon’s surface, looking at the distant Earth shining just above the horizon and the eerie landscape below. The first and the only thought I had at that moment was: “What the hell am I doing here?”)

praptak• 5 years ago

Surely astronomers have a list of objects which are expected to be interesting from a closer distance?

cmenge• 5 years ago

I guess the point is: you can't really tell anyone about it, because they have died tens of thousands of years ago. So it's "bring your friends"?!

Koshkin4• 5 years ago

I doubt it; besides, astronomers love their telescopes!

Torkel2• 5 years ago

The year is 1492. You're imagining standing on the shore of a vast continent, unexplored by your people. The only feeling/thought you have at that imagined moment is “What the hell am I doing here?”

That is perfectly reasonable! But I hope you can appreciate that the imagined feeling/thought is not shared by everyone.

stavros11• 5 years ago

That's not very comparable, because you could easily live a very fulfilling life in a new continent (well, except Australia, I guess?), but being on the surface of the moon would be a constant struggle for survival.

jasonwatkinspdx2• 5 years ago

These two situations are vastly different.

This is also a very eurocentric point of view that ignores that people were already living in the Americas. What happened in 1492 was not grand explorers finding undiscovered country in the star trek sense. It was conquerers finding a new land they were ignorant of rich with resources they could take by force via superior military power.

scotty794• 5 years ago

“What the hell am I doing here?”

I ask myself the same question whenever I leave my city.

I guess I'm not really a traveller person.

hutzlibu3• 5 years ago

Slightly related:

I just discovered Andymon.

A 1982 sci-fi novel, where a interstellar spaceship reaches the destination star, after travelling a very long, but unknown time (part of the plot).

I do not want to spoiler too much, but it was written by a academic physics/philosopher and his wife a mathematician. Deep shit. Should be standard read in schools.

drittich• 5 years ago

Do you know if there's an English translation?

hutzlibu3• 5 years ago

I assumed there is, but also could not find one right now. Would be a shame, if there isn't.

vagrantJin5• 5 years ago

You over-estimate teenagers. But worst of all, you over-estimate the department of education.

hutzlibu3• 5 years ago

I am not a fan of mandatory books, but I know I would have loved to read and talk about this book in school. It covers everything scientific, as well as philosophical existential questions.

andrewflnr3• 5 years ago

Teenagers are idiots in many ways, but also hunger for real, deep ideas. Maybe if they weren't so consistently underestimated they would take things more seriously.

jcims5• 5 years ago

The ‘specific impulse’ of a rocket engine is one measure of its ability to convert the energy in its fuel into forward thrust. Its unit is ‘seconds’, and its measure could be interpreted as ‘how long could one pound of fuel produce one pound of thrust’.

If your rocket starts off 2/3rds fuel by mass, this will result in an average acceleration of 1g as the mass of the fuel is consumed.

The most efficient chemical rockets we have today have a specific impulse in the ~470 second range. The highest specific impulse thrusters of any sort that we have in wide use today are ‘ion thrusters’, which have specific impulses in the 50,000 second range (but can’t generate much thrust at all).

So 10-12 hours at 1g is about as much as we can do with existing hardware.

Taek• 5 years ago

I've always pretended to myself that I understand what impulse means but today you've helped me actually understand it. Thank you!

fouronnes3• 5 years ago

GP is a nice reverse engineered explanation, but the actual origin of using seconds as a unit is to avoid having to compare metric and imperial units of speed. Isp is just exit velocity divided by g and it's conveniently in seconds, a pretty universal unit. And "one pound of thrust" only makes sense when you're in Earth's gravity field with gravity losses. Otherwise it's more precise to use Newtons for thrust.

HPsquared2• 5 years ago

For this kind of thing it's helpful to think about the dimensions and units involved.

In mechanics, "impulse" is a word for a unit of momentum. Momentum has dimensions (Mass * Speed), or (force * time), and can be stated in units of Newton-seconds.

"Specific" impulse is simply Impulse per unit mass of fuel (i.e. Newton-seconds per kilogram). The convention of stating it in units of seconds is based on Earth gravity (Newtons per kilogram).

If a system has specific impulse of 100 seconds, 1 kilogram of fuel would be able to accelerate a mass of 1kg at an acceleration of 1 G, for 100 seconds.

blkhawk• 5 years ago

Hours? You mean Minutes.

whimsicalism• 5 years ago

Where are you getting that from?

ben_w• 5 years ago

50,000 seconds would be 13.89 hours, though I’ll grant you “with existing technology” would preclude getting enough electrical power into an ion drive for that to do one whole gee.

Gravityloss3• 5 years ago

One very common misconception that higher specific impulse (ISP) is always good. Electric propulsion is different from chemical.

In chemical propulsion, you have the energy in the propellants. There higher ISP is better.

In electric propulsion, you use an external power source. Usually your propellant or reaction mass is inert, like Xenon. There, if you up the specific impulse but keep acceleration and delta vee the same, your power source mass increases. At some point your power source mass is a lot bigger than your propellant mass. Hence, your total mass for the same misaion would be less with lower specific impulse.

So in electric propulsion there can be too high ISP for a given mission and power source technology.

sdenton42• 5 years ago

I've heard this before, but it seems to me that the 'problem' isn't the too-high ISP, but rather the heavy power source. For rockets, we've got the rocket equation which gives the exact fuel trade-off (carrying more takes you further, but also means carrying more weight). Is there a similar 'hard' relationship between ISP and power supply mass for electric drive systems?

andyxor• 5 years ago

nuclear pulse propulsion such as in the 1950s project Orion designs was estimated to be around 6000sec (theoretically up to 100k sec) https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion

euroderf2• 5 years ago

So 10-12 hours at 1g is about as much as we can do with existing hardware.

So 9.8m/s2 times 36ks yields about 360km/s. Not bad. Altho only a thousandth of the speed of light :-(

wombatmobile• 5 years ago

American singer Elvis Presley explored this theme in 1968.

https://youtube.com/watch?v=7Skrq8unUlE

teekert2• 5 years ago

Since mass increases with speed, will this spaceship collapse and become a black hole? Or is it just massive from the observer reference frame?

nuccy• 5 years ago

Mass is not increasing in the frame of reference of the ship, so no, it will not collapse into a black hole regardless of how much energy it received externally (e.g. laser beam from Earth) to accelerate closer to the speed of light.

teekert2• 5 years ago

But it will attract massive objects (like stars) at some speed then?

FartyMcFarter• 5 years ago

Forbes's UI is infuriating.

littlestymaar3• 5 years ago

Alastair Reynolds' novel Pushing Ice (2006)[1] covers exactly this topic: a bunch of humans are trapped on an alien spaceship accelerating indefinitely, and all the involved relativistic effects are covered in the book. While it's not Reynolds best book, it's definitely worth reading just for the clarity and accuracy of the description of the relativistic effects (Reynolds is a former ESA astrophysicist).

[1] https://www.goodreads.com/book/show/89186.Pushing_Ice

milansm• 5 years ago

Which book would you consider his best? I’ve only read House of Suns, and it was great.

littlestymaar3• 5 years ago

Not an individual book, but the entire Revelation Space series is one of my favorite SF piece ever.

JamesBrooks• 5 years ago

House of Suns left me sad that it was a standalone novel, I was itching for more!

gilbetron2• 5 years ago

Definitely the Revelation Space series is awesome. For something a bit different, Revenger was really cool - it has two sequels now that are on my queue to read so I can't speak to them.

robotomir• 5 years ago

I think Chasm City is his best book, but it requires context from other Revelation Space novels to be enjoyed fully.

KineticLensman2• 5 years ago

I liked Century Rain for the well-done mix of Casablanca-style film detective noir finding himself in hard SF story

dekhn• 5 years ago

I'd read Revelation Space, Chasm City, and possibly The Prefect if you like Yellowstone and want to see what it was like before the plague.

rsynnott5• 5 years ago

Tau Zero by Poul Anderson is another one on the same line; a Bussard ramjet damaged such that it couldn't turn around. Because the Bussard ramjet provides both propulsion and radiation/particle shielding, they can't turn it off, so just get faster and faster...

javajosh• 5 years ago

Another one: The World at the End of Time, Frederik Pohl. A star being ("Wan-To") accelerates another star indefinitely, dragging its (inhabited) system with it.

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

sgtnoodle• 5 years ago

It was an interesting book, but the interpersonal dialog was rather tough to get through. It really picked up some momentum toward the end though!

snowwrestler• 5 years ago

In The Forever War by Joe Haldeman, soldiers are sent out on relativistic journeys to fight a war with aliens. Each time they come back, Earth culture has changed, and eventually it becomes unrecognizable to the soldiers, and Earthlings forget or stop caring about the war.

It was an allegory for the U.S. involvement in the war in Vietnam, in which Haldeman fought.

mlinhares• 5 years ago

This was one of the best war movies I've ever read, almost ever other one I read felt bland in comparison.

scotty794• 5 years ago

There's a pretty cool comic book based on Forever War

KineticLensman2• 5 years ago

... and Earthlings forget or stop caring about the war.

[spoilers]

Not quite. Humans develop (via cloning and other tech) to the point where they can finally communicate with the hive-mind aliens, and realise that the whole 1000-year war has essentially been a mistake from the outset.

It was an allegory for the U.S. involvement in the war in Vietnam

Yes. The obvious allegory is that to the very few baseline humans who survive the entire war due to time dilation effects the whole thing was a complete waste of time.

A key subplot in the book is that humanity adopts homosexuality such that in the latter stages of the war, the baseline heterosexual veterans are perceived as weird sexual deviants. This seems to me allegory for the difficulty Vietnam vets had in readjusting to civilian life.

dharmab• 5 years ago

[spoilers]

The main character is spacially and temporally separated from his love interest/comrade during the war. At the end, he receives a letter saying she's been in cryo sleep aboard a ship experiencing time dilation to wait for his return.

hinkley4• 5 years ago

There’s a short story in the Expanse Universe where Solomon Epstein is killed by his experimental propulsion system when it accelerates so fast that he can’t reach the controls to turn it off and then blacks out.

The drive is named posthumously after him based on the design notes found on his computer by his widow.

austincheney• 5 years ago

I remember watching that episode. Such a great series.

I think this is a slightly different phenomenon though. The problem with Epstein is rapid acceleration resulting in an increased gravitational force relative to the speed of acceleration well beyond 1g and continuing to accelerate faster until fuel is exhausted.

The scenario in the article is about indefinite acceleration. Indefinite acceleration doesn’t have to be fast to eventually reach near light speed provided enough time.

ovi256• 5 years ago

This has been depicted in The Expanse TV show, FWIW. It's a neat horror scene.

velominati• 5 years ago

Project Hail Mary by Andy Weir (author of The Martian) goes into the relativistic effects as well, and it includes a crazy (made-up) fuel that could make it possible. Great easy read: https://www.goodreads.com/book/show/54493401-project-hail-ma...

ftkftk• 5 years ago

Excellent book. The audio book is really well done as well - narrated by Ray Porter.

pierrebai• 5 years ago

I would not classify it as great, but somewhat below par. I made a list of things I did not like about the book, but it would spoil many things. Not spoiling bits:

    - All characters are two-dimensional. The further from the main protagonist, the more 2D.
    - Dialogues go from wooden to cringe-worthy, with few exceptions.
    - Protagonist swings from super over- cautious to careless and back.
    - Alien with deus-ex-machina syndrome, always having the perfect tech, material or skill to fill in the lacks of the protagonist.
    - Tired trope of amnesia to make the protagonist remember stuff progrssively for the reader.
    - Extreme over-usage of flash-back, linked to previous point, but oh boy! Half the book is flashback. Waaay over-used story-telling tech.

The science, outside of the magic fuel and magic alien material is mostly correct. That's the main strong point of the book.

deepsun• 5 years ago

At relativistic speeds, you'd be vaporized, or at least ionized by interstellar gas, e.g. there are about 1 atom of hydrogen in one cubic cm.

There was a paper considering making a shield against it, either lead, or electric field, or magnetic field, and resources required for it.

cookieswumchorr• 5 years ago

shit, looks like i started packing too early

dghf2• 5 years ago

One thing I've never been quite clear on:

If it weren’t for Einstein’s relativity, you might think that, with each second that passes by, you’d simply increase your speed by another 9.8 m/s. If you started off at rest, it would only take you a little less than a year — about 354 days — to reach the speed of light: 299,792,458 m/s. Of course, that’s a physical impossibility, as no massive object can ever reach, much less exceed, the speed of light.
The way this would play out, in practice, is that your speed would increase by 9.8 m/s with each second that goes by, at least, initially.

From the point of view of an external observer, this seems clear enough: the ship's acceleration would reduce, at first gradually, then ever more sharply as its velocity approached c.

But what about from the point of view of the ship's crew? Would they also measure a drop in acceleration -- e.g., would they weigh less?

Or would it be that they would measure the same acceleration, but the final picosecond (according to their clock), which would without relativity push their velocity to and past c, instead stretches out infinitely, thanks to ever-increasing time dilatation?

cout2• 5 years ago

As I understand, the crew would not notice any difference, since time is slowed in their frame of reference relative to that of an observer.

ruszki• 5 years ago

The crew would feel as they accelerate by a constant 9.8 m/s^2. They would not feel any slow down in time. For an external observer, the crew would never reach speed of light, but they would close the gap continuously.

JohnPrine2• 5 years ago

so after 354 days would the crew believe they had exceeded the speed of light?

api• 5 years ago

The theoretical limit is "to the edge of the Hubble horizon, as long as you don't mind it being a one way trip."

As you approach 'c' time dilation shrinks time for you. Keep accelerating and eventually a million years outside your reference frame is mere days or hours inside the spacecraft. You could travel to the Andromeda galaxy or beyond as long as you were okay never returning to Earth or returning to a different geological epoch than the one you left. Go far enough and the sun might be in its red giant phase when you get back. You may have aged a few years or decades.

This of course requires stupid amounts of energy and theoretical near maximum specific impulse, what I once heard called a "physicists' nightmare propulsion system." Something like a "photon rocket" or a relativistic velocity ion drive (propellant exit velocity near 'c') plus a very efficient fusion or antimatter reactor might be able to get you there. It was called a physicists' nightmare because if containment fails you become a flash of gamma rays in less than a nanosecond.

One of my favorite wild speculations is that hypervelocity massive particles like the "OMG particle" are the jet wash from someone's engine.

Robotbeat• 5 years ago

Can someone calculate at which point a 100 ton spacecraft accelerating at a constant 1gee (local) would have a total kinetic energy exceeding the mass energy of the entire (observable… as in, within our light cone) universe?

scotty794• 5 years ago

I'm not sure but I think that with constant acceletation, your kinetc energy raises with time squared. And the whole c speed limit just affects how kinetic energy relates to speed.

wuliwong• 5 years ago

This video from the "Cool Worlds" youtube channel is a fun walk through this idea.

https://www.youtube.com/watch?v=b_TkFhj9mgk

dctoedt• 5 years ago

One of Heinlein's juvenile novels (Have Spacesuit, Will Travel?) describes TFA's concept of accelerating at 1g until the halfway mark, then doing a "skew flip maneuver" (I think that was the phrase Heinlein used) to decelerate at 1g. [0]

[0] https://en-academic.com/dic.nsf/enwiki/2241027

jamesdmiller2• 5 years ago

Does the expansion of the universe reduce how much you have to slow down if you wish to land on a very distant planet?

platz• 5 years ago

no because expansion only happens on the largest scales

jamesdmiller2• 5 years ago

But if I travel for 45 years at 1-g doesn't the largest scale of the universe become significant to my travels?

tomxor• 5 years ago

And all at 1g... I wonder what forces the human body is capable of adapting to over a long period.

What happens if say we double the thrust, presumably halving the timescales and doubling the experienced "gravity"... would a human body be able to adapt and get stronger? or would we experience adverse side effects? (not necessarily mutually exclusive). It could even be a way to acclimatise to a different planet's mass before arriving.

[EDIT]

Looks like 2g is reasonable. The limit is higher but it sounds a bit ridiculous, astronauts would all have to compete in the strongman competitions for 4g. Any higher and we wouldn't be able to walk without breaking our bones.

https://www.discovermagazine.com/the-sciences/whats-the-maxi...

P4u1• 5 years ago

Thanks, I was wondering the exact same thing!

rtkwe• 5 years ago

That number would probably also change over time especially as people grew up in that gravity, putting more stress on their bones which should cause them to grow thicker (see ancient skeletons of longbowmen for a small example and imagine that the extra forces are there all the time).

irrational• 5 years ago

So, if you constantly accelerate for 45 years you will travel 18 billion light years to the edge of the observable universe. But, if you continue for another 45 years you won’t move beyond that point? Or do you move beyond that point but don’t reach anywhere, it’s all darkness? Or do you seem to stand still while the observable universe behind you expands past you to where you can no longer see it?

kazinator• 5 years ago

If you use as much thrust as you can, you can get wherever you are going in less time in the moving frame of reference. So that it to say, the difference between going say, 0.99C and 0.9999C is not that significant from the outside frame of reference, being just 1%, the difference in how much time slows down inside the ship is large.

dehrmann• 5 years ago

When we take a look at conventional rockets that we launch from Earth, it surprises most people to learn that they barely accelerate more rapidly than gravity accelerates us here on Earth.

This is actually pretty obvious when you look at a launch and how slowly it accelerates.

LeoPanthera• 5 years ago

This concept is explored in the second sequel to "2001: A Space Odyssey", "2061", albeit without approaching relativistic speeds.

Clarke explores the idea that in a future where fusion reactors can be built, a spacecraft can have a fusion-powered motor for which the fuel is simply water. In the book, a spacecraft travels from Earth (or maybe Mars, it's been a while since I read it) to Jupiter, and does it the "brute force" way by simply pointing at Jupiter and thrusting at 1G until they are half way there, and then turning around and slowing down at 1G until they arrive.

This has the bonus side effect of allowing the spacecraft to have normal gravity inside it.

wavefunction• 5 years ago

Forever? Seems self-evident.

btbuildem• 5 years ago

So in a way, this is time travel. If you wanted to see what the world looks like in five thousand years, you could get on a spaceship, accelerate way out to wherever and back, and voila! you've fast-forwarded five millennia.

A fascinating thought. The ship and crew would surely be long forgotten. You may be greeted as an alien visitor, until the people of that time recognize your relatively ancient technology from fragments of historical records. Too bad you speak a language nobody else even remembers.

Or perhaps you emerge as gods on a pillar of fire from the sky, witnessed by the primitive-again survivors of whatever has played out since you left.

I'm strangely tempted. If you offer me a ticket on such a ship, I might just come along.

justsid• 5 years ago

Don’t forget to become a bubble boy to avoid catching all of the new diseases that you have 0 immune system protection against.

journey_161622• 5 years ago

In 5,000 years from now the medicine will be so far ahead it would probably not matter.

wildmanx• 5 years ago

"If we never ran out of thrust, we could hypothetically reach anywhere in the Universe that a photon emitted today could reach."

versus

"I am a Ph.D. astrophysicist"

I'm confused.

In other words: How is he planning to catch up to a photon?

maweki• 5 years ago

Not catching up. But reaching the destination. That's limited though, as space expands. And any place is reachable that the photon is able to reach as these parts* are not expanding faster than the speed of light.

* The whole space between start and destination, of course

valiant-comma• 5 years ago

Saturn Run (by John Sanford and Ctien) explored using a VASIMR propulsion system to maintain long-term thrust. Without giving away spoilers, I can say I enjoyed the overall story and intrigue. Sort of hard sci-fi geopolitical thriller, and the authors did their best to avoid hand-wavy physics.

journey_161622• 5 years ago

27,000 light years in just 20 years. This is crazy, I never would have thought these relativistic effects have such impact. I guess we could create a travel into the future this way if the rocket was designed to eventually come back to Earth.

I was wondering, what if there was a spaceship circling outside the solar system at near light speed (not dwelving into whether it is possible ever to design such a ship or what the centigular forces inside would be), if there were people on such ship, that would experience 27,000 years in 20 years, would it be possible to communicate with them given the close proximity? Wouldn't it be weird that they are experiencing time in a much different way?

Heck, even with a rocket that is simply moving away from Earth, the messages that are sent should eventually reach the ship? (because it's not travelling faster than light, and at times it's even slower) How can the ship receive 27,000 years worth of messages in 20 years?

How far could a spaceship go if we never ran out of thrust? (2020)

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