Alpha Centauri - Depature: 2070 :: Back at Home: 2087

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kmarinas86

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<font color="black">An important rule for future space travelers:<br />"If you want to be home really soon, within the life time of your friends and family, you should travel at .707 c, and not any faster than that."<br /><br />If you travel too fast, your trip away from home will mean good bye forever to a generation of people on Earth. Travel slow enough and fast enough, departuring at the year 2070, and you'll be back from Alpha Centauri not so much later than the year 2087, if your stay at Centauri needn't be long.</font><br /><br />http://home.sailormoon.com/kmarinas86/alphacentauri.xls<br /><br />edit: I was wrong about this one - the spreadsheet has been edit since.

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dragon04

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Huh?<br /><br />If you travel to Alpha Centauri at c, you'd be able to make the round trip in 8.6 years' Earth time. <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

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odysseus145

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C is impossible to reach and the closer you get to c the more time becomes distorted. I'm no expert on relativity, but I think that if you were to travel at .9c then it would take significantly longer for you to get there from the point of view from observers on Earth. <br /><br /><br />edited for spelling <div class="Discussion_UserSignature"> </div>

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5stone10

Guest
I think he's referring to time dilation with regard to special relativity. Although, I'm not sure a trip to Alpha Centauri at about 3/4 c would produce that much time difference.

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dragon04

Guest
I'm still confused. The effects of time dilation increase as we approach c. But not the same way as elapsed mission time relative to Earth does.<br /><br />In other words, if we send a ship to AC at .7c, it would take 6 Earth years (relative to an earth observer) and some change for the ship to get there. And the same amount of time to get back.<br /><br />At .9c, the same thing would apply in a shorter timeframe.<br /><br />The BIG difference would occur with how much the crew itself ages during the trip.<br /><br />The elapsed mission time relative to Mission control decreases in a linear manner as the ship approaches c.<br /><br />However, IIRC, time dilation does not INCREASE for the crew at a linear rate as they approach c.<br /><br />Or am I wrong? <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

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dragon04

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Let me try to be less confusing.<br /><br />.707c to AC and back = 12.6 years earth time<br />.9c to AC and back = 8.8 years earth time<br /><br />Assuming your Dad is 40 when you leave, and lives 100 years, you have 60 years of HIS time to get as far as you can and back.<br /><br />Distance you can travel round trip and can get back:<br /><br />.7c - 21LY<br />.9c - 27LY<br /><br /><br /><br />So, the faster YOU travel increases the distance you can go in the same time frame.<br /><br />So by travelling 21LY at .9c as opposed to .7c, you get back sooner relative to your dad. Not later.<br /><br /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

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kmarinas86

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I was WRONG on this one.<br /><br /><font color="black"><font color="yellow">So by travelling 21LY at .9c as opposed to .7c, you get back sooner relative to your dad. Not later.</font><br /><br />To you it will appear sooner, but if you travel at 0.999999999999999 c, for every year of crew time, 191483958 years pass by on earth.<br /><br />You can travel .5 lightyears and back, a little more than 1 year, but with this speed by the time you come back your relatives would have died millennia ago. The year on earth wouldn't be 2005 AD, it would be 191485963 AD.<br /><br />I believe there must be a way around this.</font>/safety_wrapper>

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Guest
You'll have two acceleration & decelerations to add to that consuming over a year at 1 Earth g. I've not calculated the actual time.

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Guest
If you look out of a window, time will be going at the same old speed it always does just your clock will be different.<br />This I've never understood, as it means chemical & atomic actions for you will be slower but it's not true when looking at distant stars from Earth. I just don't understand this 'localisation' not apparent on earth.

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kmarinas86

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I was wrong...<br /><br /><font color="black"><font color="yellow">If you look out of a window, time will be going at the same old speed it always does just your clock will be different. <br />This I've never understood, as it means chemical & atomic actions for you will be slower but it's not true when looking at distant stars from Earth. I just don't understand this 'localisation' not apparent on earth.</font><br /><br />It's the spaceship that must change it's velocity, not the Earth. The change of relative velocity when the spaceship goes the other way is why that people on the spaceship turn back become "younger" than their generation of birth back on Earth. I don't know precisely why this occurs though. </font>/safety_wrapper>

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kmarinas86

Guest
<font color="yellow">Dude, I think you're really confused. It's true that if you travel very, very close to the speed of light, time for you will slow down, even though you will perceive it to be passing normally on the ship. But you are talking about traveling to Alpha Centauri, the nearest star....not to Andromeda and back.</font><br /><br />And Dragon was talking about 21 LY.<br /><br />We can present different values or change the subject but that does not mean we are confused.<br /><br /><font color="yellow">If you travel at 70% of lightspeed, the time dilation will be minimal, and the trip will be scarcely shorter for you on the ship than it will appear to be to the people who remain behind on Earth. Increasing your speed to 90% of lightspeed will cause the time dilation to increase significantly, so the trip for you on the ship will be much shorter.....but it's still only an 8 or 9 year round-trip to the folks on Earth. They will not have been "dead for a millennia" when you return.....most of them will be very much alive.</font><br /><br />True.

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5stone10

Guest
So where did you come up with the 191483958 years as the time difference?<br /><br />Looks like your spreadsheet is more in line with the consensus, which is that the time difference would be only a few years.

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kmarinas86

Guest
My Mistake...<br /><br /><font color="black">The 8th post on this thread...<br /><br />To you it will appear sooner, but if you travel at 0.999999999999999 c, for every year of crew time, 191483958 years pass by on earth. <br /><br />You can travel .5 lightyears and back, a little more than 1 year, but with this speed by the time you come back your relatives would have died millennia ago. The year on earth wouldn't be 2005 AD, it would be 191485963 AD. <br /><br />I believe there must be a way around this.</font>/safety_wrapper>

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5stone10

Guest
Again - what point are you trying to make?<br /><br />That your math is wrong, that you can do what if's on a spreadsheet?<br /><br />B.F.D.

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larper

Guest
The point being made is that the original post is so wrong it is painful, and now he is trying to dig his way out and look like he meant to post something else...<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>"If you want to be home really soon, within the life time of your friends and family, you should travel at .707 c, and not any faster than that." <br /><br />If you travel too fast, your trip away from home will mean good bye forever to a generation of people on Earth. Travel slow enough and fast enough, departuring at the year 2070, and you'll be back from Alpha Centauri not so much later than the year 2087, if your stay at Centauri needn't be long.<p><hr /></p></p></blockquote><br /><br />It don't get much wronger than that. <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

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najab

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If you were to travel to Alpha Centari at exactly C, it would take 4 years to get there, and four years to get back <b>from the perspective of an observer on Earth</b>.<p>For someone onboard the ship, no time would have passed.</p>

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kmarinas86

Guest
Wrongness...<br /><br /><font color="black"><font color="yellow">If you were to travel to Alpha Centari at exactly C, it would take 4 years to get there, and four years to get back from the perspective of an observer on Earth.</font><br /><br />But you can't travel at C because then your mass would be infinite. Unless Einstein is wrong <img src="/images/icons/tongue.gif" /><br /><br /><font color="yellow">For someone onboard the ship, no time would have passed.</font><br /><br />No time would have passed? No passage of time implies 0 change. Where is this 0 change taking place?</font>/safety_wrapper>

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spacechump

Guest
"But you can't travel at C because then your mass would be infinite. Unless Einstein is wrong"<br /><br />So fine use .9999999% of c. In any case an observer from Earth would see the space craft get there in about four years while on the spacecraft the observed passage of time for the trip would be much, much shorter.<br /><br />"No time would have passed? No passage of time implies 0 change. Where is this 0 change taking place?"<br /><br />Remember its relative. At c time is observed to stop by the photon relative to the rest of the universe. If you were a conscious photon and you traveled four light years to everything else you traveled for four years. But to you that trip would appear instantaneous even though in actuality it really wasn't.

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larper

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<blockquote><font class="small">In reply to:</font><hr /><p>It don't get much wronger than that. <br /><br />Why? What do you mean? <br /><br />When I'm talking about the a "year" in terms of numbers, I'm talking about solar revolutions of the Earth. <br /><br />Crew Years will be extended, but the actual date at which they return to Earth would be earlier. The calendar on Earth is not influenced by space travel. <br /><p><hr /></p></p></blockquote><br />Wrong. The faster you go, the quicker you get there, no matter what frame of reference you measure the time in.<br /><br />Relativity is not that hard. <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

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kmarinas86

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I was wrong... Just another mistake!<br /><br /><font color="black"><font color="yellow">The faster you go, the quicker you get there</font><br /><br />Of course.<br /><br />What I was saying is this.<br /><br /><font color="orange"><b>If you travel at .707 c</b>, Crew Years will be extended (i.e. the trip for them is longer) <b>versus travelling at .9 c</b>, but the actual date at which they return to Earth would be earlier. The calendar on Earth is not influenced by space travel.</font><br /><br />So what's your point?<br /><br />The faster you go the more time dilation. If time dilation is 9, for every "crew year" Earth makes 9 solar revolutions. What am I misunderstanding? Do have I have the concept of time dilation in reverse?<br /><br />Are you saying that if time dilation is 9, rather than 2, that fewer years will pass by on Earth for each crew year?</font>/safety_wrapper>

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jcdenton

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<font color="yellow">But you can't travel at C because then your mass would be infinite.</font><br /><br />You forgot to add "relative to an observer." <div class="Discussion_UserSignature"> </div>

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kmarinas86

Guest
<font color="orange">But you can't travel at C because then your mass would be infinite.</font><br /><br /><font color="yellow">You forgot to add "relative to an observer."</font><br /><br />Ok. I didn't know that mass could be relative....

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larper

Guest
<blockquote><font class="small">In reply to:</font><hr /><p>If you travel at .707 c, Crew Years will be extended versus travelling at .9 c, but the actual date at which they return to Earth would be earlier. The calendar on Earth is not influenced by space travel. <br /><p><hr /></p></p></blockquote><br />Keep repeating it. It is still wrong.<br /><br />Thought experiment: A neutrino and a proton erupt from the surface of AC (I use neutrino so that we avoid talking about v=c). The neutrino is traveling much faster than the proton. Say for example, that the neutrino is going .9c, and the proton is going .707c. Are you seriously saying that the proton arrives at Earth first? <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

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