Are we alone in the Universe?

[Christophe]

which means that a realistic journey at the speed of light will have to last at least two years if one does not want to undergo a painful acceleration of several g ...
But hey, we can also hope to find the trick for anti-gravity (therefore anti-acceleration). There is work ...

I said this especially to get an idea of ​​the energy and the acceleration time necessary to feel the speed of light ...

Otherwise 1G is useless for us: it is the vertical acceleration that we undergo from our birth ... the acceleration of a vessel that would accelerate to 1G would therefore be imperceptible.

I think that the human body would quite easily support between 1.5 and 2G for long periods of time, it's just the movements that will be more painful! So much the better for the muscles: they will atrophy less!

[Gaston]

...
ps: you have to undergo 1G acceleration for a little less than a year to reach the speed of light. Order of magnitude to have in mind .... then do not forget to brake In short, it is bad to go for a walk in the stars

which means that a realistic journey at the speed of light will have to last at least two years if one does not want to undergo a painful acceleration of several g ...

But to maintain an acceleration of 1g you need more and more force as you approach the speed of light.

The energy required to reach a speed V is equal to mc² (1 / √ (1-V² / c²) -1)

To accelerate 1 kg from 0 to 0,999999c, it is necessary to provide an energy of 1 * 9 10 ^ 16 * (1 / √2 10 ^ -6 -1) = 6,4 10 ^ 19 J = 1,7 10 ^ 13 kWh.

17 Tera Watt hour per kg (without taking engine efficiency into account)

[Christophe]

Ah yes anyway and there we are only talking about energy ... no technology!

I mean by that that at the moment we have not found better than action-reaction to propel in space (even if there are other ideas like solar sails) ... action-reaction which consumes a lot of on-board mass ... to take into account in the calculation what should increase tenfold 17 TWh / kg - if we talk about useful kg! Then brake too ... as said above!

Conclusion: there is more to discover the anti gravity

Otherwise we can take care of planet Earth too ... just saying...

[Janic]

Otherwise we can take care of planet Earth too ... I say that I say nothing ...

you're too down to earth!

[Christophe]

Really?

I thought I was too dreamy !!

[Exnihiloest]

... But to maintain an acceleration of 1g you need more and more force as you approach the speed of light.

The energy required to reach a speed V is equal to mc² (1 / √ (1-V² / c²) -1)

To accelerate 1 kg from 0 to 0,999999c, it is necessary to provide an energy of 1 * 9 10 ^ 16 * (1 / √2 10 ^ -6 -1) = 6,4 10 ^ 19 J = 1,7 10 ^ 13 kWh.

17 Tera Watt hour per kg (without taking engine efficiency into account)

Yes, it is considerable.
I was wondering, knowing that the total energy available on board the ship is E = m.c², what maximum speed we could reach by consuming part of the mass of the ship as "fuel", for example half. As the mass of the vessel will then decrease with time, as for a classic rocket, there would be a small integral calculation to do, a priori Ec = ∫v.dp = ∫vd (γmv) with γ = 1 / √ (1 -v² / c²).

[Christophe]

It is mandatory to keep (at least) 50% of the fuel mass for deceleration ... so the integral must be made on 100% to 75% mass for acceleration ... and 75% to 50% for the deceleration considering that 50% of the mass of the vessel is fuel ...

For integral calculus, I leave that to the maths

[Exnihiloest]

...
Conclusion: there is more to discover the anti gravity

Even with that, because it is unlikely that anti-gravity is contrary to the conservation of energy. So there will always be somewhere we need it to reach the final energy balance. Between the laws of physics and those of Murphy, there is often not much difference.

As for sen-no-sen's "wormhole", it might work but on the energy side, I think I remember that it would be insane for a hole large enough for the passage of a vessel capable of carrying passengers.

In the 19th century, physics started from almost zero, progress was spectacular, but today this is no longer the case. I think that it will first be necessary to create artificial intelligences capable of going beyond the possibilities of the human brain if we want solutions to this kind of problem.

[Christophe]

Not sure at all ... it all depends on the nature of the physical transformation ...

Before nuclear physics, no one could have imagined the considerable energy contained in atoms ... so nature can hold surprises ...

Otherwise yes for AI or the transfer of human consciousness (I am convinced that Google will get there before 2050) ... These are the themes of the (good) films Oblivion and Transcendence ... (among others ...)

https://www.youtube.com/watch?v=2LA_Na_WJe8

https://www.youtube.com/watch?v=HXNdqJF_igo

[Gaston]

It is mandatory to keep (at least) 50% of the fuel mass for deceleration ... so the integral must be made on 100% to 75% mass for acceleration ... and 75% to 50% for the deceleration considering that 50% of the mass of the vessel is fuel ...

For integral calculus, I leave that to the maths

By simplifying a bit, I think we can do without integral calculus.

If we consume 25% of the mass to accelerate, we therefore have an energy of 0,25 mc² on one side and a kinetic energy at the end of acceleration of 0,75 mc² (1 / √ (1-V² / c²) -1)

So :
1 / √ (1-V² / c²) = (0,25 / 0,75) + 1 = 4/3
√ (1-V² / c²) = 3/4
1-V² / c² = 9/16
V² / c² = 1-9 / 16
V = √ (7/16) c
V = 0,66 c

In fact, we can do a little better because we need less fuel to brake than to accelerate (because the vessel is lighter during the braking phase).

Note that "consuming" 25% of the material is much better than what a fusion engine would do: the fusion of hydrogen to produce helium consumes "only" 0,69% of the mass of the initial hydrogen.
But even with an anti-matter engine that would destroy 100% of the fuel, if we consume 49,99% of the mass of the vessel to accelerate and 49,99% to decelerate, we only reach 0,87 c

To exceed this speed, you need an engine that draws its energy from somewhere other than an on-board mass.