Steel

The thing with the beginning of the universe is that talking about a cause doesn't really make any sense, since there isn't a "before" where something could cause it. The beginning of the universe is the beginning of time and space, so how can something cause the beginning if nothing existed?

Does the start need to have a cause? ^^^Yeah you're right, I was misunderstanding your question^^^

Entropy is not limited to increasing only. In fact locally you can have pretty large decreases in entropy, so long as somewhere else the entropy goes up so that universally it increases. I got a bit lost in all your causes of causes, can you just clarify exactly what you mean by that?

I think we can all agree that any question that involves infinite pigeons is not physical, but as long as no one claims to actually be doing science here then we're all good. I think this is conversation worth having!

It's dependent on so many factors it's difficult to give a reasonable answer, but there is nothing that fundamentally stops a space-shuttle style TPS from working, albeit one that would have to be significantly more robust.

To be honest there's not a whole lot of reasoning to say why any well-designed spaceplane shouldn't be able to survive lunar reentry. The aforementioned Dreamchaser reenters from LEO at 1.5 g, so doubling that to 3 g (or even tripling to 4.5 g) shouldn't be too much of a problem for a well designed thermal tile system.

Dreamchaser is a slightly different kettle of fish to the sort of large spaceplanes you're talking about. Firstly it's a lifting body rather than relying on conventional wings, so generates less lift at small angles of attack. It's also pretty tiny, so the lift it generates is fairly insignificant when mounted on top of an Atlas V. If you get much bigger or start to use larger, more conventional wings then small errors in the guidance system (and these do happen, all guidance systems have error margins) get magnified to a point where you have significant risk of flipping the whole stack or tearing your spaceplane off of the top. Shuttle style is also pretty difficult to pull off in the craft slung on the the side of the rocket doesn't have significant engines of it's own to counter-act the massively offset centre of mass. EDIT: Ok I'm getting way too into this and I'm side-tracking the thread. I think we're going to have to agree to disagree on lunar spaceplanes and leave it at that!

Except if you factor in that you'd need to launch your spaceplane in a fairing or on a rocket with enormous stabilising fins otherwise you end up with an aerodynamically unstable launch vehicle.

I would argue a pod with a diameter the same as the wingspan of a space plane would have a much larger volume.

Even these FTL ideas floating around don't break the speed of light "properly", they're workarounds that still obey GR, so the question is still complete nonsense.

It's a contentious topic, and this thread (well the one before it anyway) has literally hundreds of pages of people arguing both sides fairly convincingly.

As others have said, welcome to real-world engineering. There's no such thing as a sub-optimal design if it meets all of it's design goal and constraints, is within budget and also fits into current infrastructure, while also not requiring additional R&D costs. The only exception is if it's so badly designed that it is obviously under-performing compared to the potential of it's components, which I don't believe for one second this is. True, the design is "sub-optimal" if you look at it from a pure maximum performance point of view, but I couldn't honestly tell you what changes you could make to remedy it without a complete redesign and concept change, and if you look at it from the point of view of the goals and capabilities that the ISRO, then its a perfectly good design. EDIT: Let's also look at in in another way. Let's say they did completely redesign the first stage to get rid of some of the inefficiencies you've mentioned. Even if they found an extra half-tonne of payload to LEO (which I would imagine is wildly optimistic), where has all that time and money actually got them? How often are they going to use that extra capability when the rocket was designed to have the capability it has now (so logically ISRO thought that very few payloads would exceed it's current capability)?

I did think about energy. However, energy doesn't tend to simplify thing to do with time, as then you need to know the change in kinetic and potential energy per unit time, which is essentially the same as knowing the change in height and velocity per unit time, so you end up with the same problem.

I appreciate your enthusiasm, but when you try to solve this taking into account changes in gravitational force you get a non-linear system of equations, which are notoriously difficult to work on and you have to be very lucky to get one with a trivial solution. The website you mention where it all boils down to an integral is either assuming constant gravitational acceleration or its an integral with no analytical solution.

This is where it get complicated. Unfortunately you can't use d =v1t +1/2 at2 because it assumes constant acceleration which, as you noticed, you do not have. None of us have regurgitated an equation because there isn't a simple one. To get your answer you have to solve a differential equation, not an integral. I can post an equation up later (I should be studying right now), so in the mean time you might want to read up on differential equations. EDIT: Ok, having now woken/caffeined up and had a look at this properly, I don't think this is a problem you can solve analytically (i.e with an equation). Unless I'm wrong (which is entirely possible) you end up with a set of coupled differential equations where change in velocity is related to the height, but change in height is related to velocity (i.e a non-linear system). Thus the only way to get an answer is to do it numerically. EDIT 2: Yeah so if you want to solve this, you'll have to assume that the acceleration due to gravity is constant all the way down (which is mostly valid close to the surface, like on Earth you would just assume 9.81 ms-2 the whole time). In that case it's pretty doable; there are plenty of examples of "Suicide Burn" (that's the name of the manoeuvre you're trying to calculate) calculators for KSP around if you Google.

Ok so lets break this down here. KSP doesn't really use either of these. Being a computer it solves things numerically, so (and this is a pretty huge simplification, possible not 100% accurate to the way it's implemented in KSP) at each time-step (roughly once per frame, but not necessarily) it calculates the force on he ship due to the gravitational body that the ship is in the SOI of. It then changes the velocity of the ship based on this force, and the acceleration is just the difference between the new speed and the old speed divided by the time between the time-steps. If you want to find the acceleration due to gravity at any given point, assuming that it is falling directly straight down with no other forces acting on it, then you can use your second equation to work out the force due to gravity and then the first equation to work out how much that is going to accelerate it. Hope this helps, please ask if I'm not clear on anything.

I don't think the growth rate has even slowed in the past 40 years or so EDIT: ok it has, but it's still over 1%

*greater than the mass of the Sun If physics has taught me one thing, it's to be pedantic

Can I also just point out that the article never mentioned that they found anything in the Atacama, just that they plan to test this technique there.

Tardigrades are already a thing I'm afraid: https://en.wikipedia.org/wiki/Tardigrade

Yeah please see the other thread on this for my quick and dirty explanation http://forum.kerbalspaceprogram.com/index.php?/topic/159131-negative-mass-created-in-lab/

You have to be careful even then, from my quick skim the method used in that paper is based on semi-classical assumptions. That's great for scattering and ionisation at low-ish energies (which are the two things the paper is looking at), but doesn't take into account the effects of the strong force, weak force or annihilation.

From what I've read, even if you only allow a single proton and anti-proton to come into contact, there's no guarantee.

Yeah, I mean with anything like this, even when you simplify it the results tend to obey some form of distribution, there will not be one particular energy that is the magic answer.

It also depends on the energy of the collision. There are numerous allowed variations that don't involve anti-proton/proton annihilation (or indeed any annihilation at all). These include elastic scattering and the formation of positronium and antiprotonic helium amongst others [1]. References: [1] S. Jonsell, P. Froelich, S. Eriksson, and K. Strasburger, “Strong Nuclear Force in Cold Anithydrogen-Helium Collisions”, Phys. Rev. A, vol. 70, no. 6, p. 62708, 2004.