Does Einstein ’s possibility of relativity imply that interstellar quad change of location is impossible ?
Paul Mainwood :
The opposite . It make interstellar travelpossible — or at least possible within human lifetimes .
The reason is speedup . man are fairly puny creatures , and we ca n’t stomach much acceleration . visit much more than 1 thousand of acceleration onto a human for an lengthy period of time , and we will have all kinds of health problem . ( Impose much more than 10 universal gravitational constant and these wellness problems will let in immediate unconsciousness and a speedy last . )
To travel anywhere significant , we need to accelerate up to your traveling speed , and then decelerate again at the other end . If we ’re limited to , say , 1.5 g for extended time period , then in a non - relativistic , Newtonian populace , this gives us a major problem : Everyone ’s travel to die before we get there . The only way of aim the sentence down is to apply strong acceleration , so we need to transmit automaton , or at least something much problematical than we ticklish purse of mostly piddle .
But relativity theory help a pot . As soon as we get anywhere near the fastness of light , then the local time on the starship dilates , and we can get to place in much less ( spaceship ) time than it would take in a Newtonian universe . ( Or , looking at it from the point of scene of someone on the starship : they will see the distances contract as they accelerate up to near promiscuous - amphetamine — the effect is the same , they will get there quicker . )
Here ’s a quick tabular array I knocked together on the assumption that we ca n’t accelerate any faster than 1.5 g. We quicken up at that rate for half the journey , and then slow down at the same charge per unit in the second one-half to stop just beside wherever we are visit .
you may see that to get to destinations much beyond 50 light yr off , we are receive massive advantages from relativity . And beyond 1000 light age , it ’s only thanks to relativistic effects that we ’re getting there within a human lifespan .
Indeed , if we bear on the table , we ’ll incur that we can get across the entire seeable universe ( 47 billion abstemious - class or so ) within a human life ( 28 years or so ) by exploiting relativistic effects .
So , by using Einstein’s theory of relativity , it seems we can get anywhere we like !
Well … not quite .
Two problems .
First , the effect is only usable to thetravelers . The Earth times will be much much longer . ( raspy rule to hold the Earth - clip for a return journey [ is to ] double the figure of light years in the board and add 0.25 to get the meter in year ) . So if they return , they will happen many thousand years have elapsed on earth : their families will live and die without them . So , even we did send IE , we on Earth would never find out what they had strike . Though perhaps for some explorers , even this would be a confirming : “ Take a trip-up to Betelgeuse ! For only an 18 year one shot - trip , you get an interstellar adventure and a bonus : time - travel to 1300 years in the Earth ’s future ! ”
Second , a more immediate and practical problem : The amount of vim it takes to speed something up to the relativistic speeds we are using here is — quite literally — astronomic . Taking the journey to the Crab Nebula as an example , we ’d need to furnish about 7 x 1020J of kinetic energy per kilogram of spaceship to get up to the top speed we ’re using .
Thatisa lot . But it ’s available : the Sun set out 3X1026W , so in possibility , you ’d only need a few second of Solar yield ( plus a Dyson Sphere ) to gather up enough energy to get a reasonably sized ship up to that speed . This also assumes you could transfer this vigor to the ship without increasing its mass : for instance , via a laser anchored to a prominent major planet or star ; if our ship needs to contain its chemical substance or subject / anti - matter fuel and accelerate that too , then you campaign into the “ tyranny of the rocket equation ” and we ’re lose . Many orders of magnitude more fuel will be needed .
But I ’m just going to airily care for all that as an engineering military issue ( albeit one far beyond anything we can attack with currently conceivable technology ) . Assuming we can get our spaceships up to those speeds , we can see how relativityhelpsinterstellar locomotion . sideboard - intuitive , but true .
This post in the first place look on Quora . Click here to view .
