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Comment by species9606 | Hacker News Reader

> I read somewhere (don't remember where) that if a ship constantly accelerates in space, it can reach another star system in a few decades and another galaxy in less than a century.

The problem is, it also has to slow down and stop at the destination. To do that, it would have to take all the deceleration fuel with it, and the amount of fuel needed goes up exponentially with the amount of deceleration required.[1] There’s no known or even theoretical form of propulsion with the specific impulse needed to get us to the next star system in under 600 years.

[1] https://en.m.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

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I skipped over deceleration because 1) our probes can transmit something significant about a galaxy even at that speed and 2) over time, we can probably figure out a way to decelerate using a galaxy's natural resources (similar to how we use a planet's gravity for slingshot)

Surely, given a century, our scientists will figure out something.

There aren’t any resources in interstellar space. It’s a near-perfect vacuum and the temperature is a uniform 3 Kelvins.

There are huge swaths of interstellar dust (mostly hydrogen) which can be used to slow the probe down.

If not, then we can use a galaxy's resources to slow us down. Basically a complex version of planetary-slingshot.

My argument is, given a century, we are likely to be able to find some way to decelerate. Consider our accomplishments in the last century (airflight, spaceflight, computers, nuclear, internet)

Sorry this may seem a little snarky but - "They will think of something" - the universal band-aid for I want it to be true but I rationally don't know how.

When ever I hear that, the optimist in me wants it to be true. The pessimist thinks otherwise and nowadays the pessimist usually wins.

We will have hotels in orbit by the 1970's - they will think of something! That was a legitimate thing that the Hiltons proposed back in the 1960's.

I used "they will think of something" as a all-encapsulating solution for what humanity will do in the next century. Predicting the next 10 yrs is almost impossible, let alone the next century.

Your example of hotels in orbit is an incorrect example. If humanity wanted to build a hotel in orbit, we would have a hotel in space (we already have a crappy hotel - ISS). I don't consider Hilton's incompetence to represent humanity's incompetence.

I don't want to defend the Hiltons but that is just one example of something that was very common during that time period. In the 50's/60's - the idea that we would not solve the fundamental issues of the era over the coming decades would have been laughable.

When it comes to material shortages, fusion power, limits of computer chip scaling, global warming, over fishing, plastic waste, hyper effective battery storage, nuclear deescalation etc... have all been answered a lot with - they will think of something. Yes, there have been improvements but with most of these things, we have also missed the mark by a long shot. And decades later, we haven't. Sometimes it is right, look at what we did with CFC's. But it is by no means something I would hitch my wagon to.

John Michael Greer calls phrases like these 'Thought-stoppers' Little saying that we have that mean we don't have to face the ugly truth of something or are just trying to be a little too optimistic about the future in the face of hard times. "Housing prices only go up", "They will think of something", "Stock prices only go up", "It is different this time", "The fundamentals don't matter any more" etc.

If it is just a probe that blasts past, that does not count as interstellar travel.

There would be very little left of a vehicle after being blasted by relativistic hydrogen nuclei for 3M years on its way to Andromeda. And, who would be listening for its report 6M years later, if it could get to Andromeda intact? Or even 500,000 years later, from one of the Magellanic Clouds?

It would make sense to gather up your whole civilization and set out at a statelier pace, perpendicular to the galactic plane, to get clear of the numerous hazards that all threaten to sterilize your whole solar system when you are in the thick of a galaxy. Then it wouldn't matter if it took a million years to get clear. Probably you induce a polar jet from the sun for propulsion, and bring the whole solar system with you. (You would leave the Oort cloud behind, sadly.)

The amount of energy required to beam a signal through galaxies far exceeds the capabilities of any probe.

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