Steel

My (slightly educated) guess is that the limit is a thermal one, rather than anything inherently limiting with the concept of HB turbofans. The turbine blades on a commercial airliner are already a marvel of materials science, aerodynamic development and structural engineering, and can (and often do) operate above the melting point of the material they're made out of; and that's at airline speeds. I imagine that if you tried to push one further than slightly supersonic (for the sake of argument let's say higher than about Mach 1.2) you'd just end up with a casing full of molten metal. There's nothing to say you couldn't design a HB engine to work at higher speeds, but if you're going to go through all the trouble of doing that, why not just design a LB engine instead, which will have a far greater specific thrust (i.e thrust per unit mass), far less complex internal and only a marginal decrease in efficiency (not to mention significantly less R&D than trying to design a HB Mach 2 engine)

You could, but none of that is anywhere near short-term, even with unlimited money. You're looking at centuries to build up a decent Dyson swarm with today's technology (which was something that the OP was quite keen on too, rather than the more outlandish Orion/antimatter/other possible-but-pretty-wild ideas)

At the end of the day, all astronomy boils down to getting photons onto a photographic plate or CCD. In that regard - and to greatly simplifying an entire field of study into one sentence - to successfully do any astronomy you need enough photons that you can distinguish what you're observing above background noise. How many that is depends hugely on what you're observing, where you're observing, the quality of instrumentation and about a thousand other factors. Of course, the more accurate you want your measurement, the more photons you want, so there is no real answer to how many you need other than "as many as possible".

I'm not aware of any fuel cell designs using kersoene and/or oxygen. Also Even if there was I don't think you'd get anywhere near the power output required from one anyway.

I guess we'll just have to wait until the end of the year/beginning of next year to see what comes out!

I don't think it was meant in that way, I think it was more of a "unlike for NASA, the military lose personnel in training accidents and on operations relatively frequently, so the PR wouldn't be as bad for them". That's not to say that any individual in the military thinks like that, but the organisation as a whole does.

You say that, but actually one of the huge issues with M-theory (and why it seems to have fallen out off fashion, possibly for good) is that it produces very few verifiable predictions.

To be honest I'd imagine it's probably a case that any damage to the mirror and you're back to square one

Not recently enough apparently! I just fired up KSP and I was in fact misremembering how good the SAS was, I thought it was better! It still is a physical effect (it still happens if you switch off SAS), but the SAS will magnify it!

I'm actually not sure it's an SAS artifact, @Abastro makes a fair point that the same effect would be present (minutely) IRL, because it is true than unless there are forces acting (which there are IRL), a plane would fly in a straight line, not with the curvature . See my last post for my attempt at an explanation.

Ok I think I've got it fairly definitively now: It will happen on Earth, but as I and others above have said, the Earth is has radius more than 10 time the size of Kerbin so the effect will be much less noticable. Add in that IRL the atmosphere is not totally stationary with respect to the ground (like it is in KSP) so you have wind, thermal pockets and a host of other effects that all affect a plane more strongly than the effect we're talking about, so it's negligible and you can't notice it!

That's what I got wrong, the SAS will actually keep it at a constant altitude (follows a vector relative to the centre of Kerbin, i.e if you set it at 10 degrees above horizon, the SAS will keep you pointed 10 degrees above the horizon) its when the SAS is off that the craft will carry on in a straight line. EDIT: actually you'll probably still see a small climb with SAS on, it's a PID system so it will be slow to react to keeping your nose pointed at the desired setting, so it will slowly drift upwards

Wait I've lost you, can you clarify what you mean?

No. Ok in my explanation above I said the SAS holds a vector in universal space. Thinking about it I don't think that's the case. It's not the SAS. The SAS holds a vector relative to Kerbin's (or whatever SOI you're in) centre, its only when you turn it off that the craft keeps itself oriented along the vector it's pointed along in universal space, unless its acted on by other forces (which it would be it you leave a spherical thing on the runway with the SAS off). This is the same reason why your craft rotates around if you turn the SAS off in orbit.

Please read my edits! So in KSP the SAS holds to a particular direction vector in the (universal) Unity game space, this is fine except if you fly an exact straight line relative to a round planet surface then it will appear from the point of view of the plane that you are getting further away from the ground (i.e. pulling up). IRL you cannot hold a particular direction vector because one doesn't really exist (there is no universal coordinate system). IRL you tend to hold an altitude (which of course is alway the same distance from sea level). EDIT: Part of the reason for this is the planes in KSP have grossly overpowered engines, so lift is not really a concern because you can just climb using engine thrust. Thus, you can fly along a straight-line vector (i.e pull up) despite the fact that you're climbing higher and thus generate less lift. IRL most planes rely much more on lift than thrust (except high performance military jets) so if you climb you generate less lift so you fall a little bit, thus you end up keeping a relatively constant altitude. Another reason is that Kerbin is tiny compared to the Earth, so even if you had a high powered military jet and pointed it along a straight-line vector, the effect would be about 10 times smaller than what you see in KSP. EDIT 2: Actually its not the SAS causing it, it's when the SAS is switched off that a craft will continue along it's heading in universal space. The reasoning above is the saem, but wherever you see a reference to the SAS holding along a vector in universal space, instead pretend I'd said that, with the SAS off, the craft will continue along that vector unless acted on by another force.

I would argue that there is no such thing as the wrong model for a situation, either your model is complete and thus can be used in any situation, or it is incomplete and therefore technically wrong! But that is just how I like to look at it!

Well then he can blame the model for being incorrect!

Technically it is incorrect. Even at low speed absolutely tiny amounts of time dilation and length contraction are happening which are not taken into account in Newtonian mechanics. The reason Newtonian mechanics still works is because they're so small that they can safely be ignored, but that doesn't mean it isn't happening.

I think he's talking about what happens when you get relativistic.

Im not sure anyone would ever get it, sadly not many people play KSP on supercomputing clusters

Carbon- and oxygen-burning does happen in the cores of very large stars once they get towards the end of their hydrogen and helium stores. But I think you might be right, by the time you accumulate enough mass to start carbon or oxygen fusion, the mass would probably just collapse further into some form of degenerate matter.

Interesting question: would the mass actually become a star as we know it? At the end of the day pigeons (like most life) are mostly oxygen and carbon, which (a) require enormous pressures to fuse and (b) fusion of these only occurs toward the end of the life cycle of a massive star. So does this mean that when it does eventually fuse would we end up with a multi-solar mass star that appears as if it's quite late on in its life cycle?

Theoretically yes, so long as the planet wasn't destroyed by the expulsion of the star's out layers when the white dwarf formed (at the end of the day the Earth will one day orbit a white dwarf if it survives the expansion of the red giant that proceeded it - which is very unlikely). Habitability is another thing though, as white dwarfs tend to put out some fairly intense UV and X-rays which don't tend to agree well with life (at least life as we know it)

Ah, but there's a fairly major difference between completely homogeneous space and no space.

I guess physically they're not that dissimilar. However, how can you have time if there is no space? What references could you possible have that differentiate one time to the next?