h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

First I would like to compliment you and H2G2 on another excellent and intresting posting.

As Einstien says light can be affected by gravity i.e. light always takes the quickest path between two points (a straight line) but can be bent by gravity, our sun for example. You were saying that just like a line round a sphere a seemingly straight line would result in a circle but surely if by line is bent but a large force of gravity acting on it then the line would not be a perfect circle. Therefore it may not even meet up on the first time round. Or have I got the wrong end of the stick.

Also to use the sphere analogy again would a line at the edge of the universe have a form a larger circle than one in the middle i.e. as with a smaller "core" inside another.

A gcse student magnasandy

One way of looking at it is that the light is bent away from some ideal concept of straightness that we hold in our heads. Another way to look at it is that there is no ideal 'straight'. The only way we have of defining straight is by the behaviour of light (and in fact that's the way that Euclid defined it), so the light it straight and it is space itself that is warped in such a way that things behave oddly while the light goes in a straight line.

Not sure whether there is an "edge" to the universe. I'm still waiting for an answer on that one.

I found an article in new scientest on tha t very intresting you cannot look at it on the internet without subscribing though it was called Fold testament: The shape of the universe in issue2581

Mass curves space-time,but what worries me is the Hubble constant,it implies space-time is being stretched (curved).Does this mean extra mass-energy is still entering the universe. And if so is it creating new particles within the cosmic voids between galaxies and stars.The particles would then gravitate toward the nearest galaxy (it might be one hypothecial explanation for dark mater), or nebula.The stretching of space-time due to the application of the Hubble constant also implies there would have been less space-time and mass-energy at the cosmic microwave background epoch. So why is there any need to assume that before this period space-time was compressed and heated,it seems to me to be more reasonable to assume that space-time continued reducing in volume to a quantum event(zero space-time).

Not sure what you're getting at there. The Hubble Constant, as far as I know, is an indication of the speed at which the universe is expanding. I don't see that that has anything to do with new particles appearing anywhere, and in the traditional "big bang" model, there are no new particles.

please note I`m not a scientist, but just trying to make sense of the Big Bang.Did find a good web site though www.astro.ucla.edu/%7Ewright/cosmo-constant.html.. it explains about ratios of vacuum energy density to critical energy density, although it didn't say why the critical density is the value they gave..the site also says the vacuum density 10Gyr ago was only 9% of total energy density,and 10Gyr from now the vacuum density will be 96% of total energy density.. so I still don't know where the energy that is still expanding the universe originates from. But if the vacuum energy keeps going up eventually something has to give.maybe another bigbang. or by a limited conversion of vacuum energy into new particles, although the Bigbang theory dosen't say much about where or why all the particles suddenly appeared, just that being hot was essential to the process.

The theory ten years ago was that the universe was expanding because it had been pushed outwards. When you throw a rock in space, it continues to travel in a straight line for ever. It's the same with a universe - the whole universe was thought to still be drifting apart because of the initial bang.

But recently they discovered that it is accelerating as if something is actually pushing it apart. I don't think they know yet what is causing it.

Imagine a simple square , then bend it in the midle, keep bending till you get one part of the square near the other part of the square.

Space is not a straight line, is a bending line. If we accept the the space there is twists, and is limited in size and time, then you can get interactions between diferents parts of the universe, cuase there is vacuum or any other kind of radiation end-up gravity hole, you can't see the other "part" of the universe.

There is no complete vacuum, particles come and go. Actually, imagine like a line, that goes from past to future, and you present is like a knife that cuts the lines, when you look at the line you only see a dot, a particle. Why one time you see it the other you don't? nobody knows for sure.
I think it is related to the fact that maybe the space time is like a rolling cylinder (if the line keeps it place independently of the cylinder, one time you see it the other you don't, you moved!).

Either way the universe is too big, and we too small...yet

I have read that the expansion of the universe provides a given cube of other wise empty space an energy density of 9.10^-10 joules/meter cubed, this is equivalent to units of pressure expressed in pascals.Gravity can be expressed in units of pressure as well, by the relation pressure P=force/seperation distance(also in pascals).If you were to assume that mass causes a reduction of the pressure within the cube by asorbing some of the expansion energy. Then gravity becomes the flow of high pressure energy density from out side the cube into the cube.So bending and twisting changes the pressure of your cube!

Dividing both sides of Einstein's equation by the cube of mass seperation distance "r" gives us, E/r^3 = M*c^2/r^3 joules per meter cubed or pascals. Remembering that t=1/f, and c=lambda*f also c^2=lambda^2*f^2 gives us, j/r^3 = (M/r^3)*(lambda^2/t^2). Energy density is proportional to, "rho" or kg/meter cubed, times the square of the wave length per second per second. Rho is a constant, it's the rate of change with time of the product of two wave lengths, that's the important fact! Remembering also energy = plancks constant times frequency E=hfn or nh/t.. Does, nh/tr^3=(M/2r^3)*lambda^2/t^2 pascals for just one half of a standing wave? Is the space-time expansion pressure due to waves? Is gravity just a reduction in the pressure of these waves? Is mass just a constant used in the equation for space-time pressure, in terms of two wave lengths inter-changing over time?

Re, my previous post, I'm not sure if "rho"(M/r^3) really is constant, since if a cube is vibrating sinusoidally, then its volume is changing in proportion to the vibration frequencys, so although the mass(of the free space vacuum, or space between masses) could remain constant, the volume changes with time, as the amplitude of the sinusoids change with time.I hope that makes more sense. Although it still doesn't answer my main question. Is the energy density of the free space vacuum, that cosmologists say the universe is mostly composed of, responsible for gravitation? Since assuming gravitational pressure is generated by the energy density of the vacuum, plugging in this value into the pressure equation for an electron, gives a close calculated figure, for it's clasical radius.

I am sorry but i am just a physic enthusiast, and i must first study the equations , before i try to develop a more mathmathical discussion by my part.

So i'll just try to talk in general terms.

vacuum has mass? isn't it just empty no time and space?

I try to think vacuum has... nothing actually. Relative vacuum i percieve has a place where no matter of sgnificant mass (upper sub-atomic lvl) exists, only small interactions.

Good point Kandarian, If a vacuum has no objects within it, supporting the property known as mass, then all you are left with are the energy field's, passing through in any directions, (such as the cosmic microwave background radiation, particles maybe, but the idea is they travel from all directions through the vacuum,all the time).

Pressure or Energy density, is the ratio of energy given by e=mc^2 divided by the separation distance cubed, r^3, in jules per meter cubed or pascals. An Electron's energy density is therefor seen to be proportional to the reciprocal of separation distance cubed. It's energy density maximum is given by e=mass of electron times light velocity squared as distance "r" approaches zero. Going out from the central zone, the electron energy density continues to diminish as "r" approaches infinity. Or in other words, an electron stretches from a central volume all the way to the edge of the universe! It appeares that the vacuum of space must be full of Electron energy density! You can use the same equation for the proton and neutron,to calculate pressure,for as large a distance as you like. Maybe that's why, when you try to find out the proton diameter or radius, on Wikipedia, its not listed,(no page available). As an electron's(or proton's, or neutron's) energy is diluted across distant space, then the amount of mass it posses and gravity it causes at that distance, will both be deminished.

Newtons equation of Force= mass,m* acceleration,g= G* m(sun)*m(planet)/separation distance squared,r^2 in Newtons, hides the mass due to the vacuum energy of the space between both masses(sun and planet)!.. since G units are volume divided by travel time between the masses squared multiplied by the hidden mass! Thus Newtons Force equation should look more like, g*m(s)*m(p)/m(G)= g*m(s)*m(p)/m(G) where both sides are equal, and m(G) is the mass due to the volume between the sun and planet. What causes this mass m(G)? Big Bang expansion energy? Or inter-mixing Spherical matter Waves? Or virtual particles? Or?... If you divide Force by area you get pressure, so dividing the force equation by area on both sides of the equals sign gives, P(s)*P(p)/P(G)= P(s)*P(p)/P(G)..the sun and the planet are both squeezing the volume between them, which would reduce the separation distance if it were not for the pressure of the planet being in orbit around the sun pushing it away.

No, I didn't understand that at all. G is a constant. It doesn't matter what units you express it in, it is constant and nothing to do with the distance between the Earth and the Sun.

"the sun and the planet are both squeezing the volume between them, which would reduce the separation distance if it were not for the pressure of the planet being in orbit around the sun pushing it away."

Meaning the gravity interactions between two huge bodies like the earth and the sun.

Are you taking into acount that there are other planets that interferes with the maths? and also the fact that the planets are not static, they are moving, cause the sun also has gravity dinamics in itself, as all the planets cause pratically all have a moving mass inside them?

So you can't imagine the system as a 2D circle, but a 3D group of diferent bodies that create gravity pulls and pushs, almost impredictable if you see it in a more precise scale, maths.

About what causes mass...if you find it please contact nobel prize judges :P and Stephen Hawking :P

I try to see mass as a thing that is. If you divide it you find even more smaller mass things, if you put it together in a more dense way you get even more potential energy, if you get mass together in groups (like forming a small planet) you get gravity.... either way you get like an infinite line of energy in space in time. And the worst part is that if you try to measure it you'll lose it's track, and if you try to track it you'll lose it's size...

I hope i am saying right things...

Thanks Kandarian, I'm still trying to figure out gravity, and like to guess as to what might cause it! The big "G" has units of volume divided by time and mass, so rearranging these units gives mass = separation distance squared times acceleration "g" divided by big"G", m(G) = r^2 *g/G ,kilograms. Hence mass m(G) is directly proportional to the area r^2. The bigger the area the bigger the mass, so the constant big G is kept constant as the separation distance increases or decreases. Well thats what I believe, can anybody disprove the above? If the separation distance causes a mass, and mass is equivalent to energy divided by light speed squared, then a volume will have mass within it, or it's equivalent energy density? So how do 2 or more masses reduce this energy density, to cause a push( attraction ) towards each other?

Thanks Gnomon, you are correct, big G is a constant, although it's underlying units can vary, and yet somehow compensate each other, to keep the magnitude of big G constant! Big G units are volume divided by mass and time squared. Volume can vary because the separation distance can be any length you like, so travel time between objects and or the hidden mass, compensate for your chosen separation distance, mass(hidden)=area*g/G. Have you seen the "cheerio effect" on wikipedia, where indentation in the surface of a liquid, is greater between 2 objects than the indentation which surrounds a single object. Could gravity work in a similar way to the "cheerio effect", but in 3D? If there is a background mass density in space, and an object reduces this mass density with distance towards the object, then 2 objects should be pushed together?

The reason why I think mass might depend on the volume, is that I came across the web site www.ann-phys.org which had a link or article, "Gravity and the quantum inertia hypothesis", the maths is a bit beyond my ability, although the idea seems sound enough, providing you believe in zero point radiation(quantum vacuum radiation field). Another alternative view is found in the "Polarizable-vacuum (PV) representation of general relativity, by, H.E.Puthoff",light speed and free space impedance depend on the permittivity and permeability constants of the vacuum, again my maths ability lets me down, and yet it seems to make sense.