# A Math of exobiology

1. Mar 5, 2016

### Fizica7

I see there are a few similar topics in this subforum so I guess this is the best place for this topic... Unless there's a dedicated exo/astrobiology subforum.

Keeping it very simple:
a) we are sentient multicellular organism on a random planet in a random galaxy.
True or false...
b) we are the only ones everywhere.
True or false...

If a and b are true then we are the rarest thing in the universe.
If a is true and b false then we contemplate c)

c) a vehicle coasting at considerable fractions of c ( v/c ), then according to relativity the t' (traveler time increment) to t (observed time increment) is:

v/c ---- t'/t
0.0 ---- 1
0.866 ---- 0.5
0.900 ---- 0.436
0.990 ---- 0.141
0.999 ---- 0.0447
0.9999 ---- 0.01414
0.99999 ---- 0.00447
0.999999 ---- 0.00141
1 ---- 0

Ignoring 1c and 0, the last line of the table for obvious energy requirements, if vehicle is traveling at 0.866c it will traverse 1 light year in 0.5 years... aka vehicle appears to travel for 1 real earth clock year, but inside occupant clock only measures 0.5 year of elapsed time, 6 months.
If it's 0.999999 then 1 light year will effectively last 0.00141 years or 12.5 hours onboard, while the destination wait 1 actual year for vehicle to arrive.
If these calculations are correct then I don't see why distances are a problem for interstellar travel as long as the traveler has no intention of ever returning home to find every loved one has aged... If exploration is the ultimate objective then then onboard time is obviously insignificant.

edit: I've inserted some lines in that "table" cause I'm not sure how it looks in desktop, on my Android it doesn't allow desktop mode for the forum.

Last edited: Mar 5, 2016
2. Mar 5, 2016

### Staff: Mentor

How do you accelerate to 0.999999 c?

If acceleration is not an issue at all, then interstellar travel is not hard. Still with the caveat that you won't ever see anyone you know again, apart from those on the same ship. Unless we find ways to make humans live significantly longer, or just go to the nearest stars within a lifetime.
But that's like saying winning any competition is not hard - just beat all opponents, the rest (??) is trivial.

3. Mar 5, 2016

### Fizica7

100g for minutes/days/weeks(depending on ly distance) acceleration then coasting at 1g, then reverse 100g before destination.

Edit: Not necessarily 100g, but for example
5g 275 days= 0.999c.....or
10g 225 days=0.9999c...or
20g 110 days= 0.9999c etc.

Last edited: Mar 5, 2016
4. Mar 5, 2016

### Alltimegreat1

It's an interesting idea, but nothing we can reasonably expect to become feasible in the next 100+ years. We can, however, take action right now and begin seeding nearby celestial objects with microscopic life. As discussed in other posts, this could involve releasing hardy microbes on both poles of Mercury. We must ensure that every planet, moon, and asteroid within reach fulfills its maximum potential for sustaining complex life forms.

5. Mar 5, 2016

### phinds

Have you done ANY research on how many G's the human body can stand and for how long?

6. Mar 5, 2016

### Ophiolite

Or, indeed, quite what propulsion system is going to deliver this acceleration for a sustained period. Generation ships would be more plausible a solution.

7. Mar 5, 2016

### Fizica7

The amount people can withstand without blacking out depends on the direction of the g-loading.
Also a very small person, like the world's smallest person from Guinness records, say 1m tall will feel g-loading half that of a person that is 2m tall, no ?
And as for the propulsion, are we talking spherical acceleration type field or virtual static field(magnetohydrodynamic) ? Or even better 2 fields superimposed(variable) to cancel out the g-loading on crew?

Edit: What's this paper from NASA about?

Edit: And what I'm unsure of if it's an actual real quote from an undisclosed "Dr. B" is:
"We also have the next level of propulsion, it is called virtual field, which are called hydrodynamic waves…”.

8. Mar 5, 2016

### phinds

We're not talking about blacking out we're talking about sustained level G force.

No, I can't even begin to figure how you came to that conclusion.

Now you're getting into magic not physics and that's not a good idea on this forum.

9. Mar 5, 2016

### Fizica7

10. Mar 5, 2016

### Staff: Mentor

100 g are both unrealistic and unnecessary. Anyway, it is not about the passengers, it is about the propulsion system.

Accelerating a single human to 0.999999 c needs an energy of about 5*1021 J. That's the current world energy consumption of 10 years. And this number is only the single human, not the spacecraft, food and so on.
To make things worse, there is no way to accelerate a spacecraft in such a way that all the energy goes to the spacecraft. Even if you would convert the whole mass of all matter in the solar system (including the sun) to a massive nuclear rocket with 100% efficiency, it would not be sufficient to reach that speed.

The parts that are not overly speculative (and marked as those) yes, but those do not allow accelerations to such high speeds.

11. Mar 5, 2016

### Fizica7

What about that NASA paper? It's also mentioned in the wiki article.
Is nobody curious to see what actually it contains and give a layman description in a sentence or two?

Last edited: Mar 5, 2016
12. Mar 5, 2016

### Staff: Mentor

It is from 1979. It mentions in the abstract (and everywhere in the main text) that the concept is highly speculative. If something would have been behind the idea, there would be follow-up studies.
They even put "propulsion" in quotation marks.

13. Mar 5, 2016

### Fizica7

Is that kind of study normal for those years, or was it ahead of its time but classified until recently? I mean does anyone remember such thermology being used in the '70s in public research institutions?
I've heard somewhere that the military/black projects are 30-50 years ahead of the public ones... any truth in that?

Edit: Aren't follow up studies in effect the ones NASA is doing with solar flare activity ?

14. Mar 5, 2016

### Staff: Mentor

A lot of weird things get studied all the time, and then get dropped - because they do not work.
"I've heard somewhere" is not a reliable source.

15. Mar 5, 2016

### Fizica7

Yeah I know it's not reliable... that's why I'm asking those with possible connections if, and only if, there is some truth to that.
So the paper mentions magnetic line merging and something to do with solar flares and there being a very big unexpected output of energy or something at the point of the magnetic lines merging.
Doesn't NASA have like at least one dedicated camera that monitors solar flares 24/7? They've been doing it for years.

16. Mar 5, 2016

### Staff: Mentor

There are tons of cameras monitoring the sun. Including the side that is not visible from Earth, via the STEREO satellites (or currently satellite, as connection to one doesn't work).
I don't see how this would be relevant to the topic.
What do you expect? Someone joining the discussion with "yeah all those rumors are true, I'm working on [whatever] which is so top secret so I cannot tell you about its existence"?
Sure, some military research projects develop things that you cannot buy on the market. But you cannot be decades ahead with projects, simply because military research relies on civil research way too much.

17. Mar 5, 2016

### Fizica7

What does that mean in therms of the best source of energy like matter antimatter annihilation? How many kg/tons ?

18. Mar 5, 2016

### Staff: Mentor

With matter/antimatter annihilation and if you magically manage to fully convert it to photons that leave the rocket in a collimated way, you would still need something like 1500 times the payload mass as fuel, half of it antimatter. And that's only the acceleration part. Want to decelerate? 3 million times the payload mass.

2*1025 J. The world energy consumption of 40000 years.
With current efficiencies of antimatter production, more like a few trillion years of the current world energy consumption.
Again, just for a single human body (of 80 kg, but a factor of 2 doesn't really matter here).

Can we agree that this is a problem?

19. Mar 5, 2016

### Fizica7

Why accelerating is 1500 times and decelerating 3 mil times ?
Edit : is it because of the increase in energy(kinetic?) you get by approaching c?
I mean if you actually wrote 3 mil seriously... Then say it takes 1500 units of energy to spin a flywheel close to c, then when I want to slow it down via an electric generator, I get 3 million units of energy? That's a deal I could take : )

Last edited: Mar 5, 2016
20. Mar 6, 2016

### Staff: Mentor

It is a result of the rocket equation. A rocket is not a flywheel, you have to carry around fuel. To change the velocity by 0.999999 c, you have to use 1499/1500 of the rocket mass as reaction mass. Starting with 3 million times the payload, you reach the speed with 2000 times the payload mass - sufficient to change your speed by 0.999999 c again (with some safety margin). You need most of the fuel to accelerate more fuel.

There are some concepts that avoid carrying around fuel, but those are all highly speculative, and most of them won't work if you go somewhere for the first time because no infrastructure exists there yet.

21. Mar 6, 2016

### Fizica7

I just don't see it... You start out with a total 1500 tons, 1 ton ship/crew/instruments and 1499 tons fuel. You get to 0.999999c then you have to decelerate so you're thinking... oooops have no fuel left to decelerate... so you go back in time lol and put an extra 1499 tons of fuel for decelerating, only now you weigh 2999 tons... So wait... Your initial 1499 tons won't cut it to accelerate to 0.999999 so you add more fuel instead of initial 1499 but then you'll need even more fuel than 1500 to decelerate... do we have a catch 22?

Edit: can't we use a solar sail in reverse like an air brake... sure space is empty but not a perfect vacuum... so even the smallest particles, striking out "brake parachute", will either rip it to shreds or get us from 0.999999 to maybe 0.99 still a huge difference on the deceleration fuel needed, no?

Last edited: Mar 6, 2016
22. Mar 6, 2016

### Staff: Mentor

Sort of. But you can directly consider the 1500 tons as "payload" you have to accelerate to 0.999999c, in order to be able to decelerate 1 ton later.
If accelerating 1 ton needs a 1500 ton rocket, then accelerating 1500 tons needs a 1500^2 ton rocket.
Oh well, realistic conditions make it even worse, because you need a ridiculous amount of shielding against anything. Every grain of sand impacts with the energy of a nuclear weapon.

23. Mar 6, 2016

### Fizica7

Well this is interesting... so a ship impacting a grain of sand at 0.999999 is like a nuke... what about the impacting something 1 mil times smaller in mass like a single particle... surely we child have the front of the ship armored to support a RPG blast... then at the destination we manufacture a new front armor and replaced the damaged one... like replacing the used disk brake on a car.
Problem is if we send a single particle(or more) ahead of us, would we be able to deliberately rear end it out would it still be going 0.999999 or would it surpass that and get maybe 0.999999999 or 1? But really concerned with that... I'm hoping there is a particle which is so massive of cumbersome that it naturally never travels at c or even 0.9 but maybe 0.899 so then even if we true it in front, it will somehow lose speed and we'll get our brake.

Last edited: Mar 6, 2016
24. Mar 6, 2016

### Staff: Mentor

Individual particles hitting will lead to radiation damage in the material, most notably at the front.
It will fly off and then it's gone. Where is the point?
That does not make sense.

Note that there is no absolute speed. Speed is always relative. And particles do not care about arbitrary reference frames. The physics is the same in every reference frame.

25. Mar 6, 2016

### Fizica7

I wanted to write not really concerned with that... but my predictive text...
Edit: and if we trow it in front.