Author Topic: 99% of Light speed  (Read 19219 times)

Offline cjackson

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99% of Light speed
« on: 08/03/2011 02:48 AM »
Is it possible to build a vehicle that can accelerate to .99 C?

How would we go about doing something like this?

If at all possible, how many centuries or millennia is it before this can be accomplished?

Could a Bussard scramjet do it?

How large would a laser/maser/gaser have to be to get the craft up to such speed?

How long would it take from the crew's perspective to cross the galaxy?

How big would the craft be? I imagine a lot of fuel would be required even if you could gather propellant along the way - Bussard scramjet. What kind of fuel would be needed?

Would such a vessel help establish a galactic civilization? Or would time dilation make implausible?

What would it look like?

Are any sort of warp drives completely impossible? If so, which of the following would best for interstellar travel: beamed propulsion, matter/antimatter reaction, Bussard scramjet, or something else?

This very fascinating for me.

Offline alexw

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Re: 99% of Light speed
« Reply #1 on: 08/03/2011 04:51 AM »
Is it possible to build a vehicle that can accelerate to .99 C?
How would we go about doing something like this?
If at all possible, how many centuries or millennia is it before this can be accomplished?
Could a Bussard scramjet do it?
How large would a laser/maser/gaser have to be to get the craft up to such speed?
How long would it take from the crew's perspective to cross the galaxy?
How big would the craft be? I imagine a lot of fuel would be required even if you could gather propellant along the way - Bussard scramjet. What kind of fuel would be needed?
Would such a vessel help establish a galactic civilization? Or would time dilation make implausible?
What would it look like?
Are any sort of warp drives completely impossible? If so, which of the following would best for interstellar travel: beamed propulsion, matter/antimatter reaction, Bussard scramjet, or something else?
This very fascinating for me.

     It's possible in the sense that the laws of physics do not forbid it. Who knows how long until it's economically possible -- if the Singularity is correct, perhaps shortly thereafter :)
    Two approaches generally deemed workable are the antimatter rocket, and beamed-laser sail. (IIRC, the Bussard scramjet is thought to have some strikes against it, but I've forgotten the details.)
     At 0.99c, gamma = 1/sqrt(1-(v/c)^2) ~=~ 7, so 100k light years for the galactic diameter would take about 100k years and would be perceived as 14k years passage of time for those onboard. 
      The size and mass of the vessel would depend on the size of the cargo. The amount of "fuel" would be unbelievable; guessing without checking the numbers, you'd want something like planetary-size solar collectors to gather the energy to power either your antimatter-producing factory or the interstellar laser.
   
      It's hard to see that a galactic civilization would be enabled by near-lightspeed sublight travel. Much easier to slowboat it and then send information around (teleporting consciousness should be easy by that time.) The possibility/impossibility of warp drives is a subject of interest to various GR theorists. There are occasional glimmers of hope ;)

     A couple of starting points you might look up are Alcubierre drive and the novel _Rocheworld_.
    -Alex
« Last Edit: 08/03/2011 04:56 AM by alexw »

Offline 93143

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Re: 99% of Light speed
« Reply #2 on: 08/03/2011 07:54 AM »
...teleporting consciousness should be easy by that time.

Assuming rather a lot, aren't you?  Considering that consciousness isn't even an objective phenomenon in the first place?

The Bussard ramjet was said to have drag issues, but I think Bussard himself said something to the effect of 'there are plenty of ways to design an interstellar ramjet so that it doesn't work'.  I'm not sure he was sold on it not being viable.

There's also the fuel issue.  They apparently found a way to catalyze proton-proton fusion so it didn't take forever, but no one's quite entirely sure what it was...
« Last Edit: 08/03/2011 08:22 AM by 93143 »

Offline Nomadd

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Re: 99% of Light speed
« Reply #3 on: 08/03/2011 11:44 AM »
 I'm pretty sure the Bussard isn't practical at near lightspeed because the power possible from a set amount of hydrogen is less than the drag from gathering it after a certain speed.
 I'd hate to hit a speck of dust at .99c.
 I'm not sure why time dialation would make it implausible. It would actually make it more plausible. If you can go something like .993c, you can travel 100 light years in 10 years. Time isn't "percieved" as being less for travelers. It is less.
« Last Edit: 08/03/2011 11:44 AM by Nomadd »

Offline Celebrimbor

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Re: 99% of Light speed
« Reply #4 on: 08/03/2011 12:00 PM »

Online Chris Bergin

Re: 99% of Light speed
« Reply #5 on: 08/03/2011 12:19 PM »
     At 0.99c, gamma = 1/sqrt(1-(v/c)^2) ~=~ 7, so 100k light years for the galactic diameter would take about 100k years and would be perceived as 14k years passage of time for those onboard. 

This always messes with my head ;D

So would they only age 14 years, over those 100 years? And if - dismissing the slowing down time etc - they carried out the return trip, they'd arrive back on Earth 28 years older than when they set out, but 200 years would have passed on Earth?

Offline Celebrimbor

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Re: 99% of Light speed
« Reply #6 on: 08/03/2011 12:36 PM »
That's right, its the accelration not the velocity that does it. And remember, you don't need to accelerate in a straight line, you can go in a circle.

Unstable particles moving at relativistic speeds in particle accelerators increase their lab-frame half life and so they don't decay as quickly as you might expect.
« Last Edit: 08/03/2011 12:37 PM by Celebrimbor »

Offline JohnFornaro

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Re: 99% of Light speed
« Reply #7 on: 08/03/2011 01:26 PM »
I gotta speeding ticket last year.  If my calculations are correct, I was only going  well under .0000001% the speed of light.  The officer didn't buy my explanation.

Gotta go.
Sometimes I just flat out don't get it.

Online Chris Bergin

Re: 99% of Light speed
« Reply #8 on: 08/03/2011 01:43 PM »
That's right, its the accelration not the velocity that does it. And remember, you don't need to accelerate in a straight line, you can go in a circle.

Unstable particles moving at relativistic speeds in particle accelerators increase their lab-frame half life and so they don't decay as quickly as you might expect.

Wow. Well there's one solution for living to see York promoted. I reckon we've got a good chance in 2173-74 season ;)

Offline Celebrimbor

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Re: 99% of Light speed
« Reply #9 on: 08/03/2011 02:06 PM »
The OP's questions are in the context of human colonisation of other stars.

But if humans became capable of generating the kind of power to move themselves around at 0.99c, then wouldn't we be more-than-capable of living in space permanently i.e. mining asteroids and Oort objects etc.?  If we can do that then why the rush to get to another star?

If you're talking about getting an unmanned scientific probe to another star as soon as possible, then 0.99c makes a bit more sense - but not much.  What's wrong with 0.5c for instance?
« Last Edit: 08/03/2011 02:11 PM by Celebrimbor »

Offline D_Dom

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Re: 99% of Light speed
« Reply #10 on: 08/03/2011 03:30 PM »
I reckon we've got a good chance in 2173-74 season ;)

Thanks for a glimpse into the future Chris, one of your finest attributes has to be your ability to think ahead  8)
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Offline Joris

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Re: 99% of Light speed
« Reply #11 on: 08/03/2011 03:37 PM »
Blue skies research will offer beyond the standard-model solutions for interstellar travel one day.
That day will come sooner than the day we will be able to travel at relativistic speeds by conventional means. (conventional should be taken with a grain of salt here  ;))
JIMO would have been the first proper spaceship.

Offline kevin-rf

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Re: 99% of Light speed
« Reply #12 on: 08/03/2011 04:04 PM »
Can someone remind me again. To date, what is the largest thing that has been accelerated to that speed? Heavy Atomic Nuclei?

Just to put this in perspective...
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Offline Rocket Science

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Re: 99% of Light speed
« Reply #13 on: 08/03/2011 04:26 PM »
We are about theoretically .05c, so we would be lucky to get 1 percent speed of light. Without some quantum leap in physics (no pun intenteded).
Regards
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Offline Lampyridae

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Re: 99% of Light speed
« Reply #14 on: 08/03/2011 04:50 PM »
This is probably where you get stuff like gravity accelerators, with powerful Kardashev-II civilisations chucking around planet-sized masses. One idea for a gravity-based accelerator was a superdense donut rapidly rotating around the toroidal axis (ie twisting). It could be spun up electromagnetically, offering the most energy bang for the buck but requires a huge initial energy investment. A small spacecraft enters, is swept up and goes whizzing out the "barrel." All with zero acceleration. It's the gravity slingshot taken to its logical extreme. It could even be an artificial, donut-shaped collapsar (I recall reading that such things were possible... as are toroidal planets under very unique conditions...). Robert Forward had other interesting ideas for reactionless drives that were plausible under modern physics (although not necessarily easy to build...)

My own version would probably rather involve a series of superdense rings, rotating as described, more like a gravitational coilgun than anything else.
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Offline Patchouli

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Re: 99% of Light speed
« Reply #15 on: 08/03/2011 06:44 PM »
We are about theoretically .05c, so we would be lucky to get 1 percent speed of light. Without some quantum leap in physics (no pun intenteded).
Regards
Robert


We already can do much better then 1% speed of light with our present knowledge of physics.

With a thermonuclear Orion 8 to 10% c can be achieved.

http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29

If we could manufacture antimatter in large amounts 50 to 80% c would be possible.

On the Bussard ramjet it also could act as a brake if the gas is captured and stored vs burned.
« Last Edit: 08/03/2011 06:47 PM by Patchouli »

Offline Rocket Science

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Re: 99% of Light speed
« Reply #16 on: 08/03/2011 06:52 PM »
Still science fiction from the mid-century... nice picture though :)
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Offline Celebrimbor

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Re: 99% of Light speed
« Reply #17 on: 08/03/2011 07:08 PM »
Can someone remind me again. To date, what is the largest thing that has been accelerated to that speed? Heavy Atomic Nuclei?

Just to put this in perspective...

Yeah, I think its lead ions in the large hadron collider. But since we're talking relativity, that collider is designed to accelerate individual protons until their mass exceeds that of a lead nucleus...

Offline Andrew_W

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Re: 99% of Light speed
« Reply #18 on: 08/03/2011 07:25 PM »
That's right, its the accelration not the velocity that does it. And remember, you don't need to accelerate in a straight line, you can go in a circle.

Pardon? The equation Alexw gives above includes velocity as a fraction of c, but not acceleration.
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Offline Nomadd

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Re: 99% of Light speed
« Reply #19 on: 08/03/2011 07:28 PM »
That's right, its the accelration not the velocity that does it. And remember, you don't need to accelerate in a straight line, you can go in a circle.

Unstable particles moving at relativistic speeds in particle accelerators increase their lab-frame half life and so they don't decay as quickly as you might expect.

 I take it you're refering to objects at different levels of a gravitational field. The difference does cause time dialtion but a coasting object at .99c has the same effect.
 And atoms in a centrifuge don't experience time dialation because of their acceleration. Differences in gravitational potential can cause time dialation, not gravitational strength. The centrifuge objects are dialated because of their speed. The same as ones in a linear accelerator are.

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