imatfaal

Are You Living In a Computer Simulation? Nick Bostrom. Philosophical Quarterly, 2003, Vol. 53, No. 211, pp. 243-255

The surface tides for a blackhole at the surface (EH) of a reasonable but undistinguished spiral galaxy (say 4million solar masses) would be a few tenths of a millimetre per second per metre *. So even two unconnected test masses would only move away from each very slowly and no spaghetification would occur outside the EH * 6e-4 m/s^2 per metre If I have my fermi estimations correct then at about 2e4 solar masses you would start to have problems (curl into the fetal position to avoid being stretched - although it might temporaraly fix a bad back) and at 10000 you would die. To be properly stretched at EH you would be down in the magnitude of 1000 solar masses and lower

Black holes we know of are dense - the smaller ones very dense. But the maths and we believe the physics allow for blackholes of any size to form - and the bigger they are the smaller the density. Check it is right before you use it!

If I have done my sums correctly [latex] m = \sqrt{\frac{3 \cdot c^6}{32 \cdot \pi \cdot G^3 \cdot \rho}} [/latex] Is the mass at which an spherical object becomes a blackhole for any given density rho tdolowy - a pleasure. Keep investigating and "doing science"

Not true at all. Any density can make a blackhole. The OP correctly gave the radius of a glass sphere (at 2400 kg/m3) which would become a blackhole. All you need is a certain mass within a certain radius - NOT a high density

Exactly. But the op is making the slightly less usual point that any density object can be a black hole provided it is big enough. For constant density the mass increases with the radius cubed - so bearing in mind that in the equation for schwarzchild radius the mass and the radius are directly related as things get higher radius thn eventually the mass within the radius is high enough to exceed that required for blackhole. It is a little contrived as such a huge sphere would compress to a higher density

You have slipped up - earth is more dense than glass and water (1 gram / cm^3) thus it will need a smaller radius to make a black hole with the DENSITY (not mass as you have put) of earth. I make it 14.1LM, 22.3LM , and 9.4LM respectively for Glass, Water, Earth. More interestingly - a black hole with the MASS of the earth would be about a 3rd of an inch across (9mm) This is the mass of a sphere (the curly p is a rho which stands for density, and r is the radius) [latex]Mass_{sphere} = \rho \cdot \frac{4}{3} \pi r^3[/latex] This is the radius of a blackhole (G and c are constants and M is the mass) [latex]r_s=\frac{2GM}{c^2}[/latex] You can work out all the figures from just these two equations - note that they both have radius and mass in them

Albert Frankeneinstein has been banned as a suckpoppet of zbigniew.modrzejewski

! Moderator Note thread locked. we already have a thread on reactionless drive nonsense - we do not need another super-spammy thread. Albert Frankeneinstein - if you have a serious question to ask or an argument to make (other than pimping a dodgy website for an even dodgier technology) then please open a new thread. Note this is a discussion forum where ideas and contentions will be tested and questioned - you do not get to soapbox

Oh my word that is a much neater solution than mine. Well done. I used Chinese remainder theorem which can be phrased thus for a set of congruences which are simultaneous as follows: [latex]x\equiv a_i(mod\ m_i)[/latex] for [latex] i=1,2,...k[/latex] if one sets [latex]M=m_1.m_2...m_r[/latex] and [latex]b_i \frac{M}{m_i}=1(mod\ m_i)[/latex] then [latex] x \equiv \left [ a_1.b_1 \frac{M}{m_1}+...+a_k.b_k\frac{M}{m_k}\right ](mod\ M)[/latex] This only works if all pairs of modulos are pairwise coprime - but if that is the case it always works. As you can see yours is so much nicer and simpler. I did mine with the help of a spreadsheet for the arithmetic

Particle/Antiparticle Pairs come into existence and vanish very quickly - they are a fluctuation that shouldn't happen according to classical physicals but must happen according to quantum field theory. Classically we can remove everything from space (the classical vacuum) - but this is a approximate situation as you will always have blackbody photons, and quantum field fluctuations. Even in a toy universe with no matter and no radiation you will still have pairs popping into existence - a zero point energy

epsilon with a little zero in subscript and mu with a little subscript are the symbols for the permittivity and permeability of free space (the classical vacuum). The zero in the subscript shows they are for free space and not for another substance - neither has the value zero epsilon_zero = 8.854810^-12 Farads per metre mu_zero = 4*pi *10^-7 Newtons per Amp^2

You do realise we can measure them? And the philosophical void empty of everything does not exist.

I think the problem with every explanation that I have seen from the experimenters is that it leaves far too much open and unsaid - which is probably why we come to such varying conclusions. And from your credentials I can assure you are far in advance of me A bit of the divine Olivia Neutron-Bomb - perfectly fitting for a physics thread

I really would not call this very simple - unless you know Chinese Remainder or are very adept with modular arithmetic then it would strike me as very hard. A few hints in the next spoiler

Agree. Just to whisper - we have got to the point of entangling macro size objects, I think mirrors; one day in the future there may be a possibility t do extraordinary things with superposition. This is the Schroedinger's cat thang - a way of merging the quantum and the macro to make a seeming paradox. But that is off topic and liable to confuse which I why I said it in a whisper

1. It is not hidden - even if you use this word inadvisedly to mean unusual or unknown it is "taken" in this context by its usage in local hidden variables which have been proven not to account for qm effects. The information is not pre-existing yet hidden from the observer - the state of particle A and the state of particle B are not defined as yet; the only state which can be defined is the superposition. This is crucial - you cannot cannot cannot get the same results for local hidden variables; it was the genius of bell to find a relatively simple experimental method to test this Not just mathematically but experimentally - the analogy was (as I think you understand) that if you measure spin on the same axis on both entangled particles (ie with a queen each time) then you always get opposite results as the spins are perfectly anticorrelated. However if you measure on two entangled particles on different axes (queen and ace) then you do not get the expected results demanded by a classical analysis. I started the analogy with the idea of the idea of using whether you can pair up your first card - ie a correlation; which is closer to the truth but it was already too complex. And in your last sentence - just to bring the point home; you do not measure two different spin states - you measure a pair of particles in superposition. You do not need two observers for "weirdness" to occur. Don't start getting into quantum teleportation before you get your head around this - or concentrate entirely on quantum teleportation and ignore this. The Bell experiment is the repeated measurement of pairs of entangled particles (whether spin on electrons or polarisation of photons) at different axes and the amount of correlation or anti-correlation between the two particles of the pair. There is no need for a second observer who has only the information passed by the entangled pair etc. Keep it simple. This, in my opinion, is the nub of the problem. There is no appropriate classical analogy - there cannot be as the results of the qm world are fundamentally odd. You can indeed work with QM by just sucking it up and doing the maths ("Shut up and Calculate" - as not said by Feynman) - but you are missing out on all the fun and just working as black box, more importantly you cannot extend your ideas if you do not embrace the divergence from the classical

Exactly what I was getting at this section "We will often assume that space is empty as we don't care about a tiny number of virtual pairs (ie when dealing with planetary orbits)" but when you are dealing with EFE you are - perforce - dealing with the large scale and you can safely not care about the tiny interactions. This is where GR falls down - it works brilliantly on the large scale but there is no crossover to the microscale, there is no harmonious link up with qm/qft ; discussions of the void as completely empty space are necessarily dealing with the small scale and thus must engage with the quantum world. And as we are talking about fields as well then there is always the Higgs field to think about

nope. Perhaps it is easier to visualize with the lighthouse analogy - you set up a lighthouse with a very strong bright laser. At a given speed of rotation and radius of observation the lightbeam will be tracking a circle at a tangential speed greater than c. But any given photon / the EMR is moving radially outwards at c

This is a physics forum - nature trumps definition. You can define space as to be empty and you have created a non-physical environment whereas in reality even the deepest void has virtual particles/zero-point energy field. We will often assume that space is empty as we don't care about a tiny number of virtual pairs (ie when dealing with planetary orbits) - but if you are dealing with the small scale and talking about the vacuum then you must not ignore the reality of the situation.

Things to bear in mind in a nice investigation: 1. M1 and M2 will feel an equal and opposite force. If they are not fixed what will happen? 2. If M1 and M2 are fixed in space - this is very unphysical . Is there a more realistic example which you could look at? 3. What happens if M1=M2 and the test object cannot split? 4. What shapes can orbits take? How do you engineer (by changing relative masses/velocities) each of them? Is this a simple question - ie can you assume what will happen or do you need to calculate, and is it possible to calculate? You might also wish to look at cathode ray tubes, or mass spectrometry. This is a very similar question - and it is something we do all the time

And remember that the shadow might track over the far distant surface at a very great speed - but changes to the shadows movement will only propagate outwards from the light at lightspeed. Information transit is still limited to c

From my reading your first paragraph is very nearly what they claim - however they claim this all happens inside the vessel. The particles are created at one end - the "field"/"environment" causes these particles to change in momentum in their passage from one end to another thus transferring the momentum to the vessel. It all sounds like the claim that firing a gun within a shipping container in space will cause the container to move as the bullets strike the end wall - this neglects that the recoil is equal and opposite and will provide exactly the same force in the opposite direction; as we know the CoM will stay put. They get around this by claiming that the change in momentum is leveraged on some sort of zero-point energy field - this is where the magic is

I went to a RS prize lecture on NMR - will see if I can dig out the video. She was a superb lecturer and I learned quite a bit

It doesn't. Even empty space is full of spontaneously appearing particle/anti-particle pairs; alternatively we could say that even empty space is permeated by a field and there is a zero-point energy. We can even measure the "pressure" that this exerts by placing two plates very close to each other - this is one heuristic explanation of the casimir effect