Don't have to go light speed, thanks to relativity. If we could achieve and sustain even 1G acceleration, live humans could make the 100LY trip in approx. 9 years (spaceship time). You could leave, visit the planet, and come back only 18 years older and tell the next-next-next-next-next generation all about it.

EDIT: To be fair, 1G over 100LY will result in a maximum speed around 0.9998c so I guess you would have to approximately approach light speed for this trip.

True, but we can only manage 1G for minutes, and even hours is a pretty far off.

Without exotic tech like anti-matter or bending space time nothing is particularly close to light speed. Even city size laser arrays are targeting 1-3% of light speed .... for a few grams!

It's a mind boggling amount of energy to get any decent fraction of the speed of light, even without the relativistic increases in mass.

cut that is half. You have got to decelerate to a near stop, much less zip past by your target.

Mo' acceleration, mo' trolley problems.

Go on vacation; come back; everyone's dead.

Alright, alright, alright.

At those speeds you will have problems with the rocket equation even if you have an mass-to-energy drive.

Is this really how time dilation works?

Speed through space + Time adds up to the speed of light or something like that (not a physicist). So as you get closer and closer to the speed of light, your motion through time (from your point of view) slows tremendously. So a few years to you, could be centuries to outside observers. Source: some Kip Thorne lectures I saw like 15 years ago.

It’s interesting that space and time are so intrinsically linked. So space “needs” time and vice-versa. I would love to be able to take an peak behind the curtain how it all works (as I think the relativity theory is rather descriptive, not the true mechanism)

I mean (so Energy is massaccel^2) so does that make space and time equal to energy.

i need a coffee for this one*

Yeah, I just try to learn a bit of the high level "understanding" of how the experts say things like time dilation work, but that's about it. I don't try to extrapolate what little I know as it would likely all be nonsense without a full understanding of the math of all of this stuff: relativity, quantum mechanics, cosmology...etc. Not that it isn't good to think about this stuff.

Yip, although there's also length contraction in play. The universe just starts contorting itself to ensure nothing ever exceeds the speed of light.

What the GP post is referring to is called a 'relativistic rocket'. You can find plenty of calculators for them, like here [1]. It leads to really mind-bending scenarios. For instance a single human could easily travel a billion light years within their lifetime, requiring "only" to travel at 1G acceleration for 40 years. Of course in that time a billion years would have really passed outside of our relativistic rocket.

If it ultimately turns out that there is no fundamental law of the universe that makes long-term rates of relatively low acceleration impossible, then the future will be a simply unimaginable place. Time itself will start to lose meaning as it becomes as variable as distance is today, at least for those able to travel.

[1] - https://www.anycalculator.com/starshipcalculator.html

Yea, the calculators really help show how wild it is. I could outlive Earth's sun by simply accelerating away at 1.25G for ~35 years (ship time), not to mention how stacked I'd be from the workout of merely existing at 1.25G for half my life. The very concept of simultaneity is completely whack at such distances, times, and speeds.

But more importantly - will we be able to do that Superman movie trick where we just fly around the sun EXCEEDING the speed of light so we can go back in time?

Joking mainly. With this much time dilation it would be fascinating to just send out tons of probes in different directions at high speed and constant acceleration - this would massively extend their service life - and potentially also massively extend our knowledge of the universe as well. Of course relatively to the people on Earth it would take a long ass time.

"The universe just starts contorting itself to ensure nothing ever exceeds the speed of light."

This pretty well describes what it's like walking around in a game. Everything looks and acts pretty normal and rational up close, yet I can walk across a continent in a few minutes, yet each individual step along the way looked normal.

Better stock up on antimatter.