Will intergalactic travel ever be possible?

[pluto2]

Technology obviously has its limits. Intergalactic travel is maybe one of these limitations. Travel to the galaxies will probably never be achieved because there is no material which is strong and durable enough to withstand lightspeed travel and the friction it causes with the plasma of space.

Turning back time or traveling back in time will also probably never be technologically possible. We can only travel to the future but we may never be able to travel to the past.

 

[JuNie]

Usually when someone says something is impossible, we'll probably find a way to do it if it's within our current realm of understanding. There is knowledge we have yet to discover so there's no point in trying to answer the actual question. So just keep seeking knowledge.

 

[Skeptical]

I agree with pluto, though for a different reason. All of the research being done on high speed anything seems to lead to the same conclusion. Nothing can go faster than light. Properly stated, the rule is " No cause and effect relationship can be propogated at more than the speed of light."

In spite of an enormous amount of effort to find a way around this, nothing has been discovered, even in theory, and nothing even looks like meeting the bill.

Therefore, assuming that is correct, travel to any other galaxy can be pretty much discounted. The nearest other galaxy that is not simply a minor one orbiting the Milky Way, is Andromeda. It is 2 million light years away. Assuming a human space vessel can one day be accelerated to 20% of light speed (about the maximum theoretically possible), it would take 10 million years to get there. I think the astronauts might be getting a bit long in the tooth by the time of arrival!

 

[cosmictraveler]

As any self-respecting science fiction fan knows, wormholes—theoretical shortcuts through space and time—make for excellent time travel portals.

It's not like scientists are looking for a way to actually travel through time. But some believe that theorizing about how it could be done—maybe by using a wormhole in space—will help them understand and perhaps even revise the laws of physics.

"Traversable wormholes are extremely useful as gedanken experiments"—the term describes experiments that can be reasoned theoretically but are impractical to carry out—"to probe the limitations of general relativity," said Francisco Lobo, an astrophysicist at the University of Lisbon in Portugal.

http://www.google.com/url?sa=t&sour...tICiCA&usg=AFQjCNHEFqo23BufORvYsiKRYIYYCZ--0A

 

[Fraggle Rocker]

Assuming a human space vessel can one day be accelerated to 20% of light speed (about the maximum theoretically possible), it would take 10 million years to get there. I think the astronauts might be getting a bit long in the tooth by the time of arrival!

Obviously a generation-starship would be required. It would presumably have to be enormous to house a large enough population to keep civilization thriving for so long. More than the six hundred people that is often suggested as the minimum for genetic health. This ship would have to be not just a city but a large city, a civilization unto itself.

As a yardstick, human civilization is only about twelve thousand years old, and Homo sapiens has only been in existence for a couple of hundred thousand years. Ancestral species that could be called less-than-modern humans split off from the chimpanzee line about seven million years ago.

So to maintain a continuous community of humans with no wars, no upheavals, no regressions back to the Stone Age, for ten million years is quite a challenge.

So is keeping an artifact of technology, the ship itself, running reliably during that time!

As any self-respecting science fiction fan knows, wormholes—theoretical shortcuts through space and time—make for excellent time travel portals.

On another thread, someone recently pointed out that the probability of creating a wormhole of greater than microscopic dimensions--much less finding a naturally-occurring one--is exceedlingly low. That generation starship will probably complete its ten-million year voyage before anybody builds or finds one.

 

[dhcracker]

when approaching the speed of light time slows down so much that no generational ship would be needed, however by the time you finish your tour of the local group even earth would be long gone. However its currently seen as impossible to go that fast.

 

[adoucette]

Assuming that we go that fast and time slows down so much, what do we think the impact will be to organic processes.

For instance, if I travelled so fast that to those on earth I'd have been gone 100 years but for me it was just 3 days, would the green bananas I took with me just be starting to get ripe?

If so, why?

And the answer isn't that time has slowed down, the answer has to have to do with the rate of chemical reactions and if they would necessarily slow down as well.

Arthur

 

[Fraggle Rocker]

when approaching the speed of light time slows down so much that no generational ship would be needed, however by the time you finish your tour of the local group even earth would be long gone. However its currently seen as impossible to go that fast.

As Skeptical noted, the obstacles to attaining speeds much beyond 0.2c are surely insurmountable. The most obvious problem is the energy requirement. I'll let someone else do the math: how much energy will it take to accelerate a ship massive enough to contain people, cargo and life support to, say 0.9c? How much more massive will that fuel make the ship? And don't forget that you'll have to decelerate at the other end of the journey, which will require exactly the same quantity of fuel.

Assuming that we go that fast and time slows down so much, what do we think the impact will be to organic processes. For instance, if I travelled so fast that to those on earth I'd have been gone 100 years but for me it was just 3 days, would the green bananas I took with me just be starting to get ripe?

Of course. That's what "relativity" is all about.

If so, why?

Unless there's a physics professor here who feels like condensing a year of lectures into a single post, you're going to need to read up on the subject yourself.

And the answer isn't that time has slowed down, the answer has to have to do with the rate of chemical reactions and if they would necessarily slow down as well.

That is absolutely incorrect; not being that professor, I can't even count the number of ways you misunderstand relativity. You really, really, really need to do a LOT more reading on the subject. Better yet, register for an upper-division physics class next semester if you're far enough along in your university course and have the prerequisites.

Relativity is heavy reading. This isn't something you can learn from a discussion on an internet board. I was accidentally admitted to Caltech and studied physics with a bunch of prodigies. We still spent a couple of weeks on relativity.

 

[dhcracker]

Assuming that we go that fast and time slows down so much, what do we think the impact will be to organic processes.

For instance, if I travelled so fast that to those on earth I'd have been gone 100 years but for me it was just 3 days, would the green bananas I took with me just be starting to get ripe?

If so, why?

And the answer isn't that time has slowed down, the answer has to have to do with the rate of chemical reactions and if they would necessarily slow down as well.

Arthur

Time is relative to the observer, so in you spaceship you will notice nothing different.. your clock ticks just the same but objects not moving relative to your velocity will from your perspective appear to go faster (not sure on that if its observable or not so bear with me), while to the stationary observer your clock will appear to tick slower. This is because the velocity through time somehow causes like a "drag" and so time goes slower. The important thing to remember when comparing moving observers to stationary observers, neither observer will agree on what happened. To one observer you appear to be slowing down, while to you they appear to speed up.

However gravitational time dilation is different, I think because its due to the actual bending of time and not due to turbulence cause by velocity. So if you had a clock on top of a very high tower with an observer stationed there, and you had the same at the bottom.. the observers then will agree to the results that the clock at the bottom ticks slower being stronger in the gravity well.

And I think the orion project useing fusion bombs can go past .2c in theory anyway... still its a worthwhile experiment we should take on I think.. repeal the no nukes in space treaty to not include spacecraft propulsion and we can do it!

 

[AlexG]

The important thing to remember when comparing moving observers to stationary observers, neither observer will agree on what happened. To one observer you appear to be slowing down, while to you they appear to speed up.

You have to realize that either observer in inertial (unaccelerated) frames may be considered to be stationary. Both observers would see the other one's time running slower. It isn't until the two frames are brought together that clocks may be compared. In order for that to happen, one or both inertial frames must undergo accelerated motion.

 

[adoucette]

That is absolutely incorrect; not being that professor, I can't even count the number of ways you misunderstand relativity.

Before I posted that question I looked to see if I could find any evidentiary proof that this was the case, that we had proof that chemical reaction rates varied relative to the speed of light and found almost nothing on the subject at all and no actual evidence to support it.

So, got anything beyond mere assertion?

Arthur

 

[AlexG]

Before I posted that question I looked to see if I could find any evidentiary proof that this was the case, that we had proof that chemical reaction rates varied relative to the speed of light and found almost nothing on the subject at all and no actual evidence to support it.

So, got anything beyond mere assertion?

Arthur

He's not asserting that chemical reaction rates vary, he's saying that the rate of time varies. And it's not relative to the speed of light, it's relative to an observer in a different inertial frame.

So if we consider the earth to be our stationary frame, a chemical reaction taking place in a moving frame would take longer according to our clocks than it would take on earth. But according to the clocks on the moving frame, the reaction takes the usual amount of time.

 

[Skeptical]

On speed of travel.

The means of accelerating a generation ship would almost certainly be to carry a whole lot of mass along, and accelerate it out the back to accelerate the ship forwards. Solar sails have other limitations.

Anyway, if we imagine that we accelerate mass at close to light speed, which is theoretically possible, using a very efficient fusion nuclear reactor for energy, it is reasonable to assume a cruising speed of 0.1 c. Note that over half the mass would be used up in acceleration, and something under half would need to be used for deceleration at the end. No fuel for a return journey, unless you picked it up at destination.

To move velocity from 0.1c to 0.2 c is not something that is possible even in theory (unless you decide not to decelerate!). However, according to a couple of NASA scientists writing in Sciam about 10 years ago, it is not unreasonable to assume that scientific progress over the next 1000 years will find a way. They were not prepared to go any further than that, and basically said that any speed above 0.2 c is essentially impossible.

 

[dhcracker]

I would point you towards the wiki "orion nuclear propulsion" article. They state so because of the dismissal of that current technology.

Though over .2 is pushing it, its closer than 1000 years for orions application

from wikis orion article:

"Later studies indicate that the top cruise velocity that can theoretically be achieved by a thermonuclear Orion starship is about 8% to 10% of the speed of light (0.08-0.1c).[1] An atomic (fission) Orion can achieve perhaps 3%-5% of the speed of light. A nuclear pulse drive starship powered by matter-antimatter pulse units would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light."

 

[adoucette]

He's not asserting that chemical reaction rates vary, he's saying that the rate of time varies. And it's not relative to the speed of light, it's relative to an observer in a different inertial frame.

So if we consider the earth to be our stationary frame, a chemical reaction taking place in a moving frame would take longer according to our clocks than it would take on earth. But according to the clocks on the moving frame, the reaction takes the usual amount of time.

I understand what is supposed to happen, my question is has it been experimentally verified and if so when and where and how?

Arthur

 

[adoucette]

I would point you towards the wiki "orion nuclear propulsion" article. They state so because of the dismissal of that current technology.

Though over .2 is pushing it, its closer than 1000 years for orions application

from wikis orion article:

"Later studies indicate that the top cruise velocity that can theoretically be achieved by a thermonuclear Orion starship is about 8% to 10% of the speed of light (0.08-0.1c).[1] An atomic (fission) Orion can achieve perhaps 3%-5% of the speed of light. A nuclear pulse drive starship powered by matter-antimatter pulse units would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light."

I don't think it's just an issue of how fast you can go, the bigger problem is how fast a massive starship can go, because if you are heading off to another star, and plan on slowing down when you get there, you are going to have to start off with a massive ship, and even if you can get sufficiant fuel on this massive ship to accelerate to 80% of the speed of light you are going to be gone a long time and thus need a large craft to sustain the people on board, so it's not just speed, it's the huge mass you need to accelerate/decelerate.

Even if you work it out using a perfect relativistic rocket where your fuel is turned into 100% of it's energy, it's a formidable problem.

Arthur

 

[ElectricFetus]

Speed is only half the issue, time is the other, can we make anything that can last millions of years of travel?

 

[AlexG]

I understand what is supposed to happen, my question is has it been experimentally verified and if so when and where and how?

Arthur

If you're asking if the relativistic time dilation has been experimentally verified, the answer is yes.

Hafele and Keating Experiment
"During October, 1971, four cesium atomic beam clocks were flown on regularly scheduled commercial jet flights around the world twice, once eastward and once westward, to test Einstein's theory of relativity with macroscopic clocks. From the actual flight paths of each trip, the theory predicted that the flying clocks, compared with reference clocks at the U.S. Naval Observatory, should have lost 40+/-23 nanoseconds during the eastward trip and should have gained 275+/-21 nanoseconds during the westward trip ... Relative to the atomic time scale of the U.S. Naval Observatory, the flying clocks lost 59+/-10 nanoseconds during the eastward trip and gained 273+/-7 nanosecond during the westward trip, where the errors are the corresponding standard deviations. These results provide an unambiguous empirical resolution of the famous clock "paradox" with macroscopic clocks."

J.C. Hafele and R. E. Keating, Science 177, 166 (1972)

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/airtim.html

If you're asking if chemical reactions have been observed to take longer when in motion, I would doubt it, as chemical reactions are far to slow to have any difference show up at the relatively low velocities we can obtain.

However, the decay of subatomic particles moving at relativistic speeds has been measured to take longer than normal (stationary), both in laboratory produced tau particles, and in the decay time of cosmic ray muons.

http://www2.slac.stanford.edu/vvc/theory/relativity.html

It would seem reasonable that if subatomic and atomic processes are measured to run slower (by our clocks) that chemical processes would too.

 

[pluto2]

Speed is only half the issue, time is the other, can we make anything that can last millions of years of travel?

The materials for the spaceship are the real problem.

The strongest human-made structures barely last a 1000 years, so I don't see how any material or any structure will be able to withstand the tremendous pressures and tearing forces of near-lightspeed travel and also do it for a million years.

 

[X-Man2]

I cannot even come close to you guy's conversation on all of this but I did want to add a couple of comments just for thought.Manmade materials may not last the length of time needed but what about in the future if materials can be made so that they can re-new themselves?Regenerating,renewing,replenishing come to mind.I was thinking if Man ever got to a point where the trip could be made then certainly materials would have been long ago been figured out as not to be a concern??

And what if for example we do get to a point where the trip could be made in 200k years and then 4k yrs after the ship leaves here on Earth we advance to the point where the trip can be had in only 50k yrs? Wouldnt the 2nd ship already be to its destination long before the 1st ship arrived in essence making the first trip for nothing?