MigL

Does time exist ? It exists in the same way length, width and height exist. We measure length with rulers, which are a length. Similarly, we measure the passing of time with an ideal clock, which is the passing of time. But no one seems to ask "What is length ?" Yet all four concepts, time, length, width and height are indispensable as tools to describe our world. Or is it a problem with the meaning of 'exist' ? One could argue that the chair you're sitting on does not exist. After all, one of the most successful theories of modern Science suggest that chair is made up of nothing but fields, which are themselves, nothing butquantities assigned to each point in space. Butwhether the chair 'exists' or not ( according to Quantum Field Theory ), there is no denying that the theory does provide useful information and valid predictions about that chair and how it behaves. So, does 'exist' refer to what something is, or does it refer to how it behaves ?

It is not hate at all. It is ridicule.

There is no 'ground zero' for the Big Bang. It happened everywhere because it is an expansion of everything, not an explosion that blasted stuff out into a void. I guess we were both right. Wikipedia links are above your level of understanding, and your understanding does seem to be at a grade 3 level.

Looking at far-away galaxies that were in the early universe at about 10 Billion years ago, we note similar galactic rotation curves, indicating that, except for a few anomalies, Dark Matter was similarly distributed and concentrated in the early universe. Since then, the expansion of the universe has undergone a continual acceleration, indicating that the Dark Energy forcing this expansion has undergone a change, IOW Dark Energy has changed in the 10 Billion year interval; Dark Matter has not. Makes it hard to imagine they could be co-dependent or related. NASA called. They said you should stop mis-interpreting their link.

Didn't we have a poster a few years back, who was very hard-headed in his views of modern Cosmology, and who also claimed to be an early investor in Apple ? IIRC, he got banned.

That's why I assumed it was at a level you could understand.

A static universe is NOT stable. Einstein originally included a Cosmological Constant term to his equations, which he later removed. "Einstein originally introduced the constant in 1917[2] to counterbalance the effect of gravity and achieve a static universe, a notion that was the accepted view at the time. Einstein's cosmological constant was abandoned after Edwin Hubble's confirmation that the universe was expanding.[3] From the 1930s until the late 1990s, most physicists agreed with Einstein's choice of setting the cosmological constant to zero.[4] That changed with the discovery in 1998 that the expansion of the universe is accelerating, implying that the cosmological constant may have a positive value" From Cosmological constant - Wikipedia The CC turns out to be a valid concept, and may, in fact, be Dark Energy.

Didn't know we had amateur 'chefs' here. Do we need a Recipe forum ?

In the second Friedman equation for the scale factor of universal expansion, the indication is that energy density and pressure ( as in the equation of state of an ideal fluid/gas ) are the governing factors. Positive energy density and positive pressure decelerate expansion. Alternatively, large negative pressure ( due Dark Energy acting like a fluid with a negative parameter in its equation of state ) will cause expansion to accelerate. The above is available here Expansion of the universe - Wikipedia Nowhere in the Friedman equations, nor in Einstein's equations for GR, is mass a determinant for expansion, or gravity, as you state ( see bolded, by me, in the quote )

I really don't understand your definition of 'inanimate' or 'animate'.

Most simple interaction at the quantum level is reversible in time. This means that if you observe a video of the interaction, it will look normal playing forward as well as backwards. ( except for the neutrino case that Joigus mentions above, and some other violations of C symmetry ) It is only when you start dealing with large groups of interactions that many more degrees of freedom make time reversal unlikely. ( a concept better known as entropy )

That's circular as 'speed' is defined as 'changes' divided by time. So, if you do a little mathematics, as us Physicists are wont o do, rearranging gives time = time ( which is not very deep ). You're going to need a better definition. One of the most tested and accurate modern theories is Quantum Mechanics ( the computer you are reading this on, proves its accuracy ). QM only allows us to glimpse, and define 'reality' when we interact with something; an interaction like bouncing light off something so we can see it, or having something impact a screen or detector, or smashing high speed hadrons into something, etc. Until that interaction happens to collapse the wave function and make that something 'real', all we have is a mathematical construct that defines a distribution of probability densities. And we know that there are no 'hidden' variables that would further define this intermediate 'reality' between interactions. So, is there an actually real 'reality' ? Is 'reality' like a computer game; a mathematical program that only displays 'reality' when the computer display 'interacts' with it ? Frankly, I don't know and don't care.; let Philosophers worry about it. As a Physicist ( I like to think ) I'm only concerned with how something affects me and other things. IOW, how something interacts with everything else. And that just so happens to be my previous definition of 'real'.

What people have been trying to tell you in this thread, is that science is not in the business of determining what something is, rather, we are interested in how it works. We know exactly how time works. Everyone's own proper time advances at one second per second, and that second is defined as the time light takes to travel the distance ct when t=1 . That's good enough.

Four posts and already three demerit points .... Word of advice. When you're new to a forum, your first post should 'test the waters', not be a verbose diatribe of 100 lines railing against the subject that is the purpose of this discussion forum. You will make a bad first impression, and no one will bother reading it.

I don't think he's preaching. I think he's drunk.

That doesn't seem a reasonable assumption. It would mean space-time is an emergent property of the matter in it, as if separations and durations are 'encoded' in the particles of matter themselves ( in a hidden variable sort of way ). My understanding is that the geometry of space-time is the field, not space-time itself. Space-time devoid of geometry is equally un-physical. The reason vacuum solutions are un-physical is because there is no true vacuum devoid of anything. But ... I could be wrong.

You cannot 'see' an extension along the time axis, as that implies an 'outside' PoV. If you understand the concept of the block universe, you must realize that you are embedded in it. There is no outside.

True. But we know of no mechanism for producing such Black Holes. Stellar gravitational collapse produces BHs that are an order of magnitude more massive than our Sun; and they are much colder than the CMB. Extremely small BHs of the size you mention, could only have been produced by primordial density fluctuations of the hot dense plasma of the very early universe, and they would have, and be, evaporating. Yet we look around the universe, and back in time, and we don't see the tell-tale gamma ray bursts indicative of the final moments of these primordial BHs. There may just not be any.

In simple terms, intrinsic curvature implies there is no 'outside' dimensions embedding the curvature. Since there is no 'outside' you cannot 'see' a ship dropping below the horizon as your view is confined to the curved surface. The Earth's surface is extrinsic because you can go 'inside' the curvature by boring a hole between two points connecting the ends of an arc, or 'outside' the curvature to see the top of the mast of the ship dropping below the horizon. Not sur I agree. Global geometry is also determined by the mass/energy content of the universe, and this global curvature constrains possible topologies. As an example, a negatively curved universe can not close on itself, and has to be infinite. A flat universe can either be infinite or finite, as there are flat closed topologies like a flat torus. A positively curved universe has only closed topologies, like hyperspheres or toruses, available which are necessarily finite. If the universe is homogenous and isotropic, we may be able to use the local curvature of the observable universe as an indication of the global curvature of the universe, and all measurements indicate it is very nearly flat. That could mean the universe is finite but many orders of magnitude larger than the observable universe; much like the floors of your house are flat on a curved Earth, or it could actually be flat and infinite.

You're having problems imaging the topology of 4D space-time by comparing it to 3D or 2D topologies ? Welcome to the club. Mathematics, however, has no such limitations.

The 'block' universe is an interpretation. One of many, and the one you are choosing to use is called 'eternalism' and has many counter-arguments. See here for other interpretations

No paradox; classical and quantum mechanics don't mix. Black holes do not allow for the emission of anything, under classical considerations. Black Holes do have entropy, however, and so, an associated temperature. This temperature is barely above 0oK, and since the universe is currently at 2.7oK, BHs are actually net absorbers of mass/energy. It is only in the far future, when the universe has cooled below a BH's temperature that it will experience net evaporation due to Hawking radiation. Both Hawking radiation and the information paradox ( due to unitarity requirements ) are quantum mechanical considerations, and cannot be explained classically.

I don't know the mathematical motivation. The Physical motivation is the elimination of divergences in the perturbative corrections of Quantum Field Theory.

The temperature when the universe becomes transparent, and electrons can 'stick' to hydrogen nucleii, is basically the ionization temperature ( energy ) of Hydrogen. At higher temperatures atoms cannot bind, and you have a radiation filled plasma that is opaque like the Sun. As the present CMB temperature is 2.7oK , that indicates ( according to gas laws ) that the universe has expanded to over 1000 times its size since the recombination era.

As an extremely small mass ( compared to the mass of the Sun ) makes no difference whatsoever in Newton's equation, we can make that 'assumption' to ease the calculation. That doesn't mean light does not have the property of mass; it is massless, otherwise it could not move at c . And light is NOT energy, but it does have that property. Ooops. My mistake. As genady correctly points out above, a flat torus has no curvature, and even a 'regular' torus is only curved along one axis.