[creesch]

Just going to recycle this comment I made in reply to an almost identical comment as yours. I don't think you folks realize how big space actually is.

The speed of light is 1079 252 848 km/h, the fastest space craft ever made was the Parker Solar probe (using a sling shot) clocking in at 692 000 km/h. So at that speed it would take, 1559 years to travel one light year.

This planet sits at a distance of 48 light years, so it would 74 832 years to get there. Just for good measure, when it gets there it would also take 48 years for us to know that since radio travels at the speed of light.

Note, that the speed of the spacecraft I mentioned was the peak speed. Space is big, really big.

[chrsw]

Science fiction has entertained and inspired millions of people and we should all be grateful for that but it has also distorted what people think space really is.

When you consider the scale of space it becomes pretty understandable why the Milky Way isn't teeming with civilizations sending large amounts of mass all over the galaxy. A realization one comes to despite the facts that it has taken humans a blink of an eye (on a galactic timescale) to go from tools to rockets and the Milky way is billions of years older than the entire history of the Earth.

[RetroTechie]

We simply don't kow.

On a scale of probable -> less probable, you have:

Self-organizing chemicals -> replication -> evolution -> multi-cellular life -> creatures that move around -> intelligent life -> use of tools -> basic technology like wheels, steam engine -> industrialization -> advanced tech -> automation -> space faring -> capable of interstellar travel -> capable of intergalactic travel. Powered by energy sources of increasing complexity/sophistication & scale.

This whole evolution requires a stable environment. Dinosaur-killing asteroid & it's back to square 1. Also (for example) how would intelligent life on a waterworld (which basically excludes electronics as we know it) become space-faring?

So it's not unlogical to expect that microbial life could be 'everywhere', tool-using intelligent creatures are rare, and interstellar-capable civilizations are so few & far between that (on average) they're just too distant in space or time.

Doesn't matter who visits who if neither party can cross the ocean in between.

[teachrdan]

I blame Star Wars, kinda. Watching it with my kid, I can't help but notice that everywhere they travel in space -- even by accident -- they end up by a planet that can support human life in terms of temperature, atmosphere, and gravity. Mandalore (the Mandalorian home planet, natch) has a moon that doesn't only support life; it also has the exact same gravity as Mandalore!

Sentient life in hospitable environments is as unavoidable in the Star Wars universe as it is absent in ours.

[globular-toast]

Project Hail Mary does a pretty good job, although probably doesn't come across in the film. SF that doesn't even bother using wormholes or some other FTL travel (e.g. warp speed) is quite annoying, though.

[creesch]

I mean, even there they pretty use the Astrophage as a plot device to fill in the huge gap in technology needed to cover those distances. They make it clear that they would have no chance to cover those distances without the Astrophage, but it is very convenient.

[globular-toast]

Sure, it's fiction. But at least there is a device.

[leobuskin]

If I understand correctly, time spent within this interstellar ship reference frame would be significantly less than 75k years. And at 1c speed, 48 years on Earth would be ~2 years of "flight" for the passengers, correct me if I'm wrong.

[creesch]

You are not wrong, but it still wouldn't make a whole lot of difference. First of all with any technology we currently have, including hypothetical proposals, we can't even get close to 1c. The best we can do, and this assumes purely hypothetical unproven ideas, is accelerate to a fraction of the speed of light. Acceleration itself will take up a significant amount of time and even then we are nowhere near the speed of light. Project Orion would in theory be able to do 3% to 10% of the speed of light. That's about the only proposed propulsion we actually have the technology for in the sense that we might be able to build it this decade.

So let's be optimistic and assume we can reach 10% of c (unlikely), that is 10 years for one light year, meaning that it takes about five centuries. Practically speaking 10% of c is unlikely, it takes about a month to accelerate to those speeds you'd need an insane amount of mass in the form of bombs to explode to just get up to speed. Which is why 3% is more "realistic". Oh, did I mention that there is no realistic way to slow down either? In theory it is just detonating the same amount of bombs in front of the craft, but in order to take that mass on your journey you'd need a lot more mass to get up to speed and the numbers get silly rather quickly.

So "realistically" at 3% of c we are talking about roughly 1500 years to just speed past our target.

Also, the original remark was about sending probes, not humans. But at 3% or 10% of c time dilation isn't much of a factor either so you'd need a generational craft if you want to send people.

Again, space is big, really big.

[eaenki]

Man, that’s not how intelligence works. Eventually if a civilization doesn’t blow itself up, it will achieve anything, and it’s not incremental steps. Speed has never been incremental steps. in 1810 you would’ve been thinking about faster horses or some shit like that. Def not rockets. OP said hundreds of years. In hundreds of years from now our rulers will definitely have that kind of tech, whatever tech it is.

[bluGill]

Often technology is approaching an asymptotic limit that it will not go beyond. Know about a hand waving will change the laws of physics. There's every reason to believe that the speed of light is a maximum that we will never be able to choose because it requires infinite energy. While it is true we don't know everything, and there are certainly parts of it we don't know, the things we do know will have to obey and predict the things that we currently do know to be true. The laws of relativity, although annoying, are very good at describing things. If anything replaces relativity, it's going to replace it while still predicting exactly the same things that relatively does that we have verified. That doesn't leave much room for a theory that might and faster travel.

[creesch]

> Def not rockets. OP said hundreds of years.

Yeah to reach it with current tech. No shifting goal posts, thank you very much.

> In hundreds of years from now our rulers will definitely have that kind of tech, whatever tech it is.

Also, I should point out that technological progress isn't linear and guaranteed. Also, "our rulers" what ...?

[teaearlgraycold]

If we’re talking about human technology available in a few hundred years, don’t discount far more exotic options. I’ve heard people talk of theoretical terrestrial lasers pushing on tiny probes. With an absolutely gigantic laser and magical material at the back of the probe that won’t instantly vaporize there’s enough energy to get something the size of a smartphone up to a reasonable proportion of the speed of light.

I can’t prescribe this theoretical technology to the problem. But I also think it’s unreasonable to set the limit using known technology and then discount the idea altogether. We have no idea what will be possible in 300 years.

[mr_mitm]

Note that you can't use these lasers to slow down the probe, which will dramatically limit the things the probe can do at the destination. I'm not even sure what kind of interesting things a probe the size of a smartphone could do, let alone phone home.

[perilunar]

> you can't use these lasers to slow down the probe

You can, but you need a couple of solar sails. You beam the laser at the sails to accelerate, then at the halfway point one of the sails detaches and becomes a reflector, which lights up the now flipped probe and remaining sail to decelerate them.

[throwawayben]

send an unending chain of them and you solve the transmission problem _and_ they don't have to slow down as you'll always have another on the way past whatever you're targeting

[zelphirkalt]

How many times the Earth's materials would we consume doing that? And wouldn't it block ma lazor from reaching the previous probes and accelerating them?

[pandoro]

Exactly. Imagine what would be possible after a billion year of technological evolution, heck even just 100'000 years. We already know that space time metric engineering is theoretically possible within our current understanding of physics, we don't have either the technology or access to energy density necessary to do it. And that's only within our limited understanding of how the universe works.

[jl6]

If you have a billion year long civilization, it would probably be easier to genetically/medically engineer humans to live forever, so that a 75,000 year space voyage doesn’t seem so long. Easier than near-lightspeed space travel at any rate.

[jimbokun]

Could you expand on what “space time metric engineering” is?

[pandoro]

The general idea is to deliberately shape the geometry of spacetime to allow for effects such as faster-than-light travel (relative to another region of spacetime).

Einstein's field equations link geometry to matter and energy:

G_μν = 8πG/c⁴ · T_μν

Left side describes how spacetime curves (the metric tensor). Right side represents what's causing the curvature (the stress-energy tensor): mass, energy, momentum. The usual approach is: you specify T_μν (what matter is where) and solve for the resulting curvature. Metric engineering takes the backward approach. You pick the geometry you want first: e.g a bubble that carries its contents faster than light relative to the outside universe. Then you work out what T_μν would have to be to produce that geometry: what distribution of energy and stress the equations demand.

The classic example of spacetime metric engineering is the Alcubierre drive.

The limitation with this is that the required T_μν has negative energy density in some regions (the bubble walls) which violate some assumptions about how "reasonable" matter behaves. But Quantum Field theory allows such local regions of negative densities and we have created such regions in labs experimentally already (Casimir effect). We "just" don't know how to sustain the effect at bigger (atomic) distances.

[perilunar]

At the distances involved even the beam from a gigantic laser will be spread out enough not to vaporise anything — you won't need a magic material, just a very large, thin, and highly reflective solar sail.

[ourmandave]

Seriously even the nearest star is 6,200+ years at Parker probe speed.

[globular-toast]

The comment you replied to doesn't appear to be misunderstanding the size of the galaxy, they mention acceleration to near the speed of light so they're probably thinking 100 years to get there and another 48 to receive signals back. The missing part is the propulsion system capable of doing that.

[creesch]

> The missing part is the propulsion system capable of doing that.

That is a pretty big missing part. Not as big as the galaxy, but still huge.

[Den_VR]

> the fastest space craft ever made was the Parker Solar probe (using a sling shot) clocking in at 692 000 km/h…

After 44 days of acceleration. On a multi-millennia mission we’re talking a velocity likely 300x what the Parker Solar Probe achieved (while falling into the Sun).

[tgv]

I think we can't even build a radio transmitter that covers 48 light years.

[jimbokun]

I want to know what future technologies could accelerate an object to a significant fraction of the speed of light.

What kinds of scientific breakthroughs would be required? Could those breakthroughs be achieved in the next 2 or 3 centuries?

[creesch]

> I want to know what future technologies could accelerate an object to a significant fraction of the speed of light.

With all due respect, this has been extensively debated online and is extremely easy to look up.

> Could those breakthroughs be achieved in the next 2 or 3 centuries?

Any predictions on future scientific breakthroughs are wishful thinking. Even directions that seem promising at some point can end up being dead ends and we simply don't know what we will or will not achieve.

With current technologies, even hypothetical ones we can't get there in a time period that is under a few centuries at best and over a millennium at worse. Even for the centuries figure we'd require technologies we haven't been able to crack yet.