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Author | Topic: Is Faster Than Light travel the wrong question? | |||||||||||||||||||||||
kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:What is your goal? What are you trying to achieve? Meldinoor explained things pretty well, I think. At near the speed of light you could travel a large distance without aging very much. You would want to accelerate as fast as tolerable for as long as possible, perhaps even for half the travel time, then decelerate the same way. An acceleration of 1G for 1 year would give a relative velocity of about 0.7 c, and you would age at about 70% the normal rate. You'd need multi-G's of acceleration for multi-years to get large factors of time dilation. The energy expenditure for this would be enormous, of course. That's why sci-fi scenarios of sending people to colonize distant planets are complete fantasy. It would require an energy source which is nearly infinite and essentially free. Edited by kbertsche, : Bad back-of-envelope calculation. Edited by kbertsche, : Added correct values for 1G and 1 year.
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:You lock your mindset into a particular technology (wind power). I specifically did NOT do this. In addition, your analogy is poor. The wind speed wouldn't need to be unimaginably high, just high and steady.
quote:No. My comments are not locked into "20th-21st century way of thinking." They are locked into physical reality. But they allow for new energy sources. quote:No. My comments do not depend on "our limited understanding of physics." I have explicitly left room for new energy sources and new physics by saying that this "would require an energy source which is nearly infinite and essentially free." For a society which is worried about energy costs and limited energy availability, sending large groups of people to colonize distant planets is pure fantasy. Doing so would require a new energy source, and we would no longer be a society which is worried about energy costs and limited energy availability.
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:No. I am superposing reality and what we know of physics. quote:Transporting matter at relativistic velocities requires energy. Transporting matter is the topic of the OP and the thread. If you want to consider some sort of non-material travel (astral projection or whatever), that's fine, but it is not the topic of the OP. If you want to imagine a universe where all of the laws of physics are completely different than ours, that's fine, too. But it is completely disconnected from reality. It is pure fantasy.
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:This was no doubt a commonly-held conception, and it was certainly a technological challenge. But can you point to a reference where science said this was impossible? quote:String theorists are certainly trying to understand these things in a fundamental, theoretical way. But can you point to any physicists who are actually "working on this sort of thing" with a goal "to make the trip shorter" for human transportation?
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:Yes, if we were at such a point technologically, such travel would be simple. quote:They are back-of-the-envelope calculations (literally), and should be accurate to 10% or so. quote:There's nothing wrong with 1G at all for an entire lifetime, of course. But this only gets you to about 0.7 c after a year, where things are just starting to get relativistic. It would be preferable to accelerate at 2G or more to further reduce the time. quote:Exactly. This is the fundamental problem. It puts a very high cost on the process, and this would be true for any society where energy cost is at all significant. These things are fun to speculate about, but they are not realistic in the foreseeable future. They certainly are not realistic until/unless we solve our energy problems. I am frankly surprised at the resistance that such comments meet in this thread. There seems to be a quasi-religious conviction here that mankind will be able to do such things one day. I consider these sci-fi speculations to be in the same vein as (but even less realistic than) global floods or vapor canopies.
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:Yes, but it's not possible to accelerate hard enough and safely enough to reduce this to a few days. Jet pilots in pressurized suits can endure a few Gs (less than 10?) for very short periods. Even if you could somehow get to 12G's, it would still take a month to get to 0.7 c where things begin to get relativistic. I invite you guys to check my back-of-the-envelope math. Here's a brief explanation of it:1G acceleration is about 10 m/s^2. 1 year is about 3x10^7 seconds. So in a non-relativistic world, 1G for 1 year would take you to a velocity of 3x10^8 m/s. This just happens to be the speed of light, making things convenient. We haven't actually gotten to this velocity, of course, because of relativistic effects which we have ignored. But with a fixed force of acceleration for a year, we HAVE imparted the same momentum as in the non-relativistic case, a momentum equal to c times the rest mass (p = m0c). The total energy is then sqrt(2) times the rest energy, and the velocity is 0.7 c. Edited by kbertsche, : clarified?
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:Centrifugal force from a rotating wheel can only add acceleration; it can't reduce it. This only makes things worse.
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
I wrote:
Transporting matter at relativistic velocities requires energy.
quote:My approach is not closed minded; rather, it is grounded in reality. Einstein theorized an equivalence between matter and energy and this has been experimentally verified. Hence my original comment. If you wish to transport matter at relativistic velocities without using a tremendous amount of energy, you would have to disprove Einstein's E=mc^2 relation and to explain why all of the experimental evidence of it is wrong. You are free to theorize about such fantasies as much as you wish.
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:In which case you are not only accelerating the spaceship, but also the mini-neutron star. This takes immensely more energy than just accelerating the spaceship, only reinforcing the point that you would need a new, inexpensive energy source first. Also, the "neutron matter" needs to be far enough in front of the spaceship that its gravity gradient won't rip the ship and people apart.
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:It would be foolish to lock one's predictions to present-day technology. But it is equally foolish to think that our experimentally-verified understanding of relativity is completely wrong. And if our understanding of relativity is basically correct, physical travel (i.e. transportation of matter) with large accelerations requires a large amounts of energy. Like it or not, new technologies, new energy sources, or new physics cannot change this. The only way to change this is to disprove our experimentally-verified theories of relativistic dynamics.
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kbertsche Member (Idle past 2161 days) Posts: 1427 From: San Jose, CA, USA Joined: |
quote:Yes, Newtonian mechanics is still an excellent approximation over the parameter space where it was experimentally verified. And I expect Einsteinian relativity will likewise remain an excellent approximation over the parameter space where it has been experimentally verified. Thus there is no realistic hope of physical travel to distant planets without a tremendous expenditure of energy.
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