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Comment by marcyb5st | Hacker News Reader

Yeah, it is and the math get's really counterintuitive to grasp since humans (at least me) have trouble thinking in exponential terms.

If you accelerate at 1g constantly for 1y you travel 0.5 light years. You do that for 10.5 years and you reach the center of the milky way. You do that for another 4 (~14 total) years and you are in the Andromeda galaxy, and you do that for another 10 years (~24 years total) and you reach what today is considered the edge of the observable universe.

By the time you get there you are basically traveling at a rounding error from C.

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> If you accelerate at 1g constantly for 1y you travel 0.5 light years

Can't we accelerate past 1G constantly? Or do we expend so much energy doing it that we can't realistically do it with today's technology?

We can't necessarily survive that well when under acceleration greater than 9.81 metres per second per second for extended periods of time.

Gravity on Earth varies about .7%.

Increasing the acceleration a little bit more than that (eg to 1%) would make a difference.

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

> "Increasing the acceleration a little bit more than that (eg to 1%) would make a difference."

Wouldn't that be only a few months on a decades-long journey at 1.01G vs 1G??

I was thinking of journeys that are hundreds or thousands of years.

If the acceleration was too great but survivable, what happens? I can’t imagine my back, knees or ankles would like it.

We can easily accelerate past 1g... 1g is just chosen for human comfort, but running any rocket engine continuously for a year requires an impossible amount of fuel.

We need a massive rocket to escape the earths gravity (1g). That takes us minutes and a crap ton of fuel. The issue is to keep doing that with fuel and oxidiser constantly for 1, 2 or 10 or 25 years is a monumental amount of energy, which is a monumental amount of weight, which is a monumental amount of volume... Also you also need the exact same amount of fuel to stop again.... So yeah ... We don't got it yet

We can't do it with any rocket-like propulsive technology. By the time you get anywhere close to c the front of your spacecraft is being abraded into nothing by interstellar gas, larger particles of dust will kill you, and colliding with anything bigger creates an explosion that can be seen for light years. You need to be flying a large asteroid to even think about surviving it - you still won't for long, but you will have time to think about it - and the energy requirements are wildly impractical.

Magic warp bubble tech is the bare minimum, and we're nowhere close to inventing that.

Sadly there is no realistic approach to get there (even assuming fantasy-levels of technology).

Chemical rockets are currently the only thing that allow sustaining such accelerations briefly for human-size payloads, but the low exhaust velocity and exponential reaction mass requirement make sustaining it for days/months/years completely impossible.

You'd have to supply the energy externally (i.e. some sort of beam propulsion), but getting any significant fraction of g out of such a system (with human-sized payloads) seems unlikely within the next centuries, especially as the distance increases.

> You'd have to supply the energy externally (i.e. some sort of beam propulsion), but getting any significant fraction of g out of such a system (with human-sized payloads) seems unlikely within the next centuries, especially as the distance increases.

Or some form of ram scope, plenty of H everywhere, but those also have the issue of you collecting things while going at relativistic speeds.

You need ablative ships cruising ahead of you..

Not with current technology. That was kind of the physics “trick” in the book ‘Project Hail Mary’, where the astrophage provided enough energy and propulsion to be able to sustain 1G of acceleration.

The astrophage was pumped around the ship to act as shielding for cosmic rays too.

> Can't we accelerate past 1G constantly?

It's hard to accelerate at or beyond 1G for very long with current technology. Roughly speaking, the rocket runs out of fuel soon. Packing more fuel makes the rocket heavier, meaning diminishing returns when using the fuel. The mass required grows exponentially. See "The tyranny of the rocket equation"

> You do that for 10.5 years and you reach the center of the milky way

But that would be pretty pointless without taking the time to decelerate :)

oh, so that’s where all the aliens are … up and cruising around at .99g

> math get's really counterintuitive to grasp

People always say that about speed of light stuff, but I don’t get it. Do you have any more examples of counterintuitive math?

Because what you’re describing is basically the equivalent to compound interest in finance. (e.g. investing $100 at 10% interest over 10 years results in $260)

One million seconds is 11 days, a billion seconds is 31 years.

Thanks! But same here imho:

              1,000 seconds =          ~0.01 days (~17 min)
          1,000,000 seconds =         ~11.57 days (~12 days) 
      1,000,000,000 seconds =     ~11,574.07 days (~32 years)
  1,000,000,000,000 seconds = ~11,574,074.07 days (~32k years)

It all seems quite logical once you put everything into the same unit, I think.

Maybe it's just our human calendar/time unit rollercoaster (60*60*24*30*12) that's playing tricks on us here.

Of course it is logical, we are not discussing the math.

But it isn't intuitive, you're not used to numbers that big or that grow that fast.

Few things go from a million to a billion, especially when related to time.

It’s the units that make it seem unintuitive. 12 days is roughly 0.032 years, and 17 minutes is likewise 0.000032 years. It’s relative to how we were taught to view smaller lengths of time. Of course you could argue measuring time by the rotation of heavenly bodies is more intuitive than counting on your fingers for the hours in a day and days in a lunar cycle.

Going from a million to a billion isn't some special relationship. It's just * 1000. It's the same as going 11000 or 101000.

I find it frustrating that people seem to think that someone going from 1M to 1B is somehow different to other numerical operations. It's not. It's 1000 times bigger, it's not a huge deal.

And any exponential growth is also a multiplication, it's not a big deal, just giving example on what they asked before.

Somehow people are interpreting this as some kind of math trick.

It's not a trick, our brains are not wire to deal with numbers growing quickly, but we do understand the math.

Only abstractly. If you are living in the process, it is hard and very few people live that.

Which process, though? Every human alive easily went from millions of cells to billions of cells to trillions of cells.

The proper time (that is, the time the traveler measures on a clock) goes to zero very quickly towards the end. Even with both axes plotted logarithmically, it's just a sudden drop at the end towards light speed.

- [pic](https://home.davidgoffredo.com/hackernews/proper-time-one-li...)

- [plot](https://home.davidgoffredo.com/hackernews/proper-time-one-li...)

Links seem to be broken?

No, but IPv6 only these days. I never set up dynamic DNS.

Can you explain for dummies how... a normal person with a normal web browser should access this?

Enable ipv6

Not an option for me. I have a residential ISP that gives me symmetrical gigabit fiber, but has no support for IPv6.

Have an IPv6 connection.

So basically "go fuck yourself" if your ISP does not yet support IPv6?

I'm not saying that I couldn't fire up Cloudflare Warp, but I think it's a legit issue for average users [0]?

[0] https://xkcd.com/2501/

Funnily enough, I use Cloudflare Warp at work, and it breaks my site for what I think are DNS related reasons. Maybe there are some more exotic DNS keys that I need to add.

Or I could go back to IPv4 with dynamic DNS, but that would mean changing domain registrars.

NS record for domains usually can be pointed at someone else than the registrar it's on, just fine(unless DNS infra of either one or both goes down). That's entirely separate to registrar transfer.

Still can switch isp usually

I don't see any AAAA record for your domain.

Interesting

    david@carbon12:~ $ dig +short AAAA home.davidgoffredo.com
    2603:7000:5101:de1c::cafe:babe

I'll have to look into it, thanks for the QA testing everyone.

I am on IPv6 and I cannot access your site.

ftfy

pic: http://numpad0.com/imgs/home.davidgoffredo.com/proper-time-o...

plot: http://numpad0.com/imgs/home.davidgoffredo.com/proper-time-o...

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