Another theoretical possibility is that any Alien life that is exploring the universe could be more resistant to acceleration / deceleration than we squishy humans are.

Perhaps they figured out AI or have made space-adapted biological life forms that can survive constant acceleration at 25Gs and are sending them out to scout the universe for other life, and once they find it they would signal back to the home planet.

25G of constant acceleration would kill any human, especially if it were maintained for the time it would take to approach light speed, but for an AI or a creature specifically developed to survive that it would make a trip to the Solar System from Alpha Centauri take 5-8 years.

Then again, if they could do 1G of constant acceleration that would only add like 2 years to the total trip. Long enough to be one-way for most people but short enough to be survivable under ideal circumstances.

Assuming they stopped outside of Neptune's or Pluto's orbit they would still have a few years of travel to make it to Earth but they would have started detecting our broadcasts long before arriving.

I'm not saying this happened, rather that it becomes plausible when you take some liberties with the starting conditions.

▲ nobody9999 7 days ago | parent | next [-]

>25G of constant acceleration would kill any human, especially if it were maintained for the time it would take to approach light speed

>Then again, if they could do 1G of constant acceleration that would only add like 2 years to the total trip. Long enough to be one-way for most people but short enough to be survivable under ideal circumstances.

It would take ~2 weeks to to approach light speed while continuously accelerating at 25G. It would only take ~1 year to do so at 1G continuous acceleration.

On cosmic time and distance scales, those are essentially the same, especially since once we approach the speed of light, there's no going faster.

As such, tolerance for G forces seems pretty irrelevant for interstellar travel.

Doing so within the confines of a solar system is another matter altogether, I'd expect.

▲ BizarroLand 7 days ago | parent [-]

Humans die under 10g for more than a few minutes. Admittedly, we could position the humans to be in the optimal direction, but even 2g sustained for months would undoubtedly cause issues.

I picked 25G as it would be an insane but reasonable acceleration, and time is always a factor. Trimming 2 years off of a voyage might seem worthless on an intergalactic scale, since once you are more than a few solar systems away you're on the scale of AI scouts and generation ships, but for a close star like Alpha Centauri, 2 years (each way) might be the difference between a one way death march and the possibility of a heroic return home.

▲ zeven7 4 days ago | parent | next [-]

Grandfather paradox says the riders on the ship won’t experience most of the time of the ride

▲ nobody9999 3 days ago | parent [-]

>Grandfather paradox says the riders on the ship won’t experience most of the time of the ride

No. The Grandfather Paradox[0] says nothing of the kind:

   The consistency paradox, commonly known as the grandfather paradox, occurs 
   when the past is changed in any way.[5] The paradox of changing the past 
   stems from modal logic: if it is necessarily true that the past happened in a 
   certain way, then it is false and impossible for the past to have occurred in 
   any other way, so any change to the past would be a paradox.[13] Consistency 
   paradoxes occur whenever any change to the past is possible.[6]
   
   A common example given is a time traveler killing their grandfather before 
   their parents' conception, thus preventing the conception of themselves. If 
   the traveler were not born, they could not kill their grandfather; therefore, 
   the grandfather proceeds to beget the traveler's ancestor who begets the 
   traveler. This scenario is self-contradictory.[5] One proposed resolution for 
   this paradox is that a time traveller can do anything that did happen, but 
   cannot do anything that did not happen.[5] Another proposed resolution is 
   simply that time travel is impossible.[14]

[0] https://en.wikipedia.org/wiki/Temporal_paradox

	▲	zeven7 2 days ago \| parent [-]
		Sorry I spoke quickly. I meant the twin paradox and reached for the wrong label

▲ JumpCrisscross 6 days ago | parent | prev [-]

> Humans die under 10g for more than a few minutes

With no air?

	▲	BizarroLand 5 hours ago \| parent [-]
		It's not about the air. Its about our fundamental squishyness. At 10g, a 150lb man would weigh 1,500 lbs. His heart isn't strong enough to move blood that suddenly weighs 90lbs/gallon that also has to push other blood that also weighs that same amount. His blood vessels, paper thin and easily torn under normal weight, suddenly have 10 times the amount of pressure to resist. He's fine for a few moments, jet pilots experience short bursts of 10g during flights quite often, occasionally more. Might pass out after 10-20 seconds, but after 10 minutes, his brain, starved of oxygen and squished under its own weight, ceases to function. His heart or his blood vessels rip and tear from the strain, and his body falls apart inside of its own skin. It's not pretty, but it would probably be a fairly painless way to go. Getting back to your question, his ability to breathe is not relevant under those situations. The absence of oxygen would accelerate his demise no more than it would under any other situation.

▲ jandrese 6 days ago | parent | prev [-]

A fun exercise is to calculate how much mass in rocket fuel you would need to accelerate at 25G for two weeks. Or even to accelerate at 1G for a year. Even if you assume a ridiculously high ISP like 1 million seconds (our current best engines are around 8,000 ISP, and they're severely limited in thrust) and close to unlimited energy to add to the mass. Like you're using antimatter to kick propellant out the back at relativistic velocities.

Now add in the mass to slow down once you begin to approach your destination.

	▲	BizarroLand 6 days ago \| parent [-]
		I know I am not taking relativity into account but outside of that it's something like 250 kilograms (~550lbs) of antimatter (and that value again for the matter for it to react to) or the equivalent in other fuels. The only difference is how quickly you burn through it. Which doesn't sound like a lot but its probably as much or more antimatter than exists in the entire solar system, so if it were the fuel then whoever was using it would need to have figured out a method to create and store antimatter in bulk along with the ability to react antimatter as rocket fuel without destroying the rocket its fueling.