Yesterday, I gave a talk titled "Human Space Exploration: from Tsiolkovski to Time Peake" to the Plymouth Astronomical Society, and talked at the end about interstellar travel. I explained how relativity means you can get to any star in the galaxy in the lifetime of those travelling (but not those left on Earth) if you can accelerate quickly (to avoid the effects of general relativity on time), get close to the speed of light (c) and cruise, then special relativistic time dilation slows everything down on the ship. It works a bit like suspended animation but without the need for cryogenics. For example, if you accelerate for an Earth-year at 9.8 m/s^2, then cruise for 23 Earth-years at 0.9c, then decelerate equally quickly, you can get to Gliese 667 (which is Earth-like and 23.6 light years away) in about 25 years as measured from Earth and only 12 years as experienced on the ship. I then made the crucial point that travel agencies are not yet offering package tours to Gliese because accelerating to 0.9 times the speed of light takes over 300 times the energy generated by our civilisation in a year.
Not to worry: there are a few bold suggestions for how to get to 0.9c, including antimatter rockets that are propelled by radiation from, for example, electron-positron annihilations, interstellar ramjets that focus and fuse hydrogen collected in deep space, so they avoid carrying heavy fuel and so can accelerate more easily, and Alcubierre drives that bend space and unfortunately need negative matter. I also mentioned my own suggestion (McCulloch, 2013) which is a MiHsC-drive which, like the ramjet, avoids carrying fuel. It is shown in this schematic:
The circle in the centre is the spacecraft core, and it holds in front of it a metamaterial shield (the dashed curve on the left) that can damp Unruh waves. If the spacecraft is accelerated it will see Unruh radiation as shown by the red & orange wavy lines all around it. If the metamaterial shield is set up the right way it will disallow waves in front of the spacecraft (left) so there will be fewer there (the orange wave has less amplitude) and the craft will feel more Unruh radiation pressure from the back then from the front and this will accelerate it forward (the black arrow), and it will do it without the need to carry fuel. The fuel, like the ramjet, is available en route: in this case from the quantum vacuum, made inhomogenous by a manmade horizon. Note: I think the emdrive is inhomogenising the vacuum in a similar way (see McCulloch, 2015).
McCulloch, M.E., 2013. Inertia from an asymmetric Casimir effect. EPL, 101, 59001. http://arxiv.org/abs/1302.2775
McCulloch, M.E., 2015. Testing quantised inertia on the emdrive. EPL, 111, 60005. http://iopscience.iop.org/article/10.1209/0295-5075/111/60005
Finding a metamaterial able to shield the unruh radiation might be really challenging. Also, it would means that gravity comes from matter shielding radiations.
Interestingly enough, many gravity anomalies aren't explained by classical mechanics but by some radiation pressure theory (EMRP for ex). See http://www.blazelabs.com/f-g-intro.asp
Classified as fringe physics... You're warned. But again, thinking out of the box can sometime be good. This theory has the merit to fit observational data at least.
I so sad to see such good ideas disregarded by so many people because it breaks the newton/enstein mantras...
Keep the good work Matt. :)
I don't understand all of that, but the concept of ramjet is very interesting.
Does EmDrive in fact pump the vacuum like a jet-ski?
In the ship's frame it takes about 1.43 years to get to 0.9c, while it's about 2 years for observers at rest. The total displacement is 1.25 light-years. If we reverse the process, then the total time/displacement is 2.46 years and 2.5 light years.
High cruise speeds could face hazards from the interstellar medium, but I suspect a good magnetic field would divert most of it. So, suitably protected, one might as well accelerate the whole way, flipping over at the half-way mark to decelerate. In that case relativistic time-squeeze becomes really significant.
isn't the metamaterial shield going to have pressure against it? (the waves that it doesn't let through)
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