[John369 (OP)]

Please help me answer these questions:

1. How can past, present and future exist all at once? Many light years away, alien lifeforms would still be seeing dinosaurs on earth since only dinosaur earth light has had time to reach alien lifeforms so far, but how can earth's future be seen? How is future also predetermined? Does it have to do with special relativity and light cones?
2. Please explain eternalism and block universe in simple terms. Sorry I was always dumb and I am unable to understand this.
3. Is our 4D universe flat and exist on the surface of 5D hypersphere? Is the hypersphere expanding?
4. Is it really impossible to see the present of a distant planet? Could some abstract higher dimensional perspective(eg. God/programmer) see all of simultaneously existing time since 3D beings can only see time as being very subjective? Are we even 3D?

[CPT ArkAngel]

To answer questions 1 and 2, you need to understand two basic principles.

The first principle is the principle of relative simultaneity due to the limited maximum speed of energy transfer, the speed of light in the vacuum. From the point of view of Einstein, this is the limit of causality. Therefore, two simultaneous events are relative to your place in space and time. Think of two different observers looking at lightnings and one sees two of them at the same time while the other sees them happening one after the other. As it is define as the speed of causality, it implies that there is no definite simultaneity.

The second principle is the conservation of information which can be related to the conservation of energy, though they are not necessarily equal. This principle just says that the information of the structure of the universe cannot be destroyed. It means that if you have the mathematical solution to the entire universe and a complete set of variables and parameters, you can predict the future and reconstruct the past (supposing you have the right computer).

According to Einstein, and this is probably true, if you could see the entire Universe from your own perspective and take a picture of it and you learn from it all information content of every particles and pieces of it, you could know everything, past and future. But it is true for any observer, even though their passage of time is different. As there is no preferred spatial coordinate or time, you cannot distinguish what is real and what is not apart from your own perspective. When you consider that all massive particles are observers and they have all their own perspective which must be equally real, then you have the Block Universe. Remember that you must exclude the possibility of an absolute time reference, an absolute simultaneity and faster than light causality. General Relativity does not respect the principle of the conservation of information due to the singularity at the center of black holes in his equations. Einstein knew his theory was not complete and no black holes were observed at the time. Most physicists think information is conserved and there is a limit and therefore no real singularity. Personally, I think Einstein went too far by eliminating these possibilities and the necessary limits are the keys to find the correct answer. The now has a special meaning in cosmology, this is where the symmetry of the expansion is conserved and energy is always conserved locally in General Relativity.

[alancalverd]

Please help me answer these questions:

1. How can past, present and future exist all at once?

They can't, by definition of "all at once"

, but how can earth's future be seen?

It can't because the light that signifies it hasn't been emitted.

How is future also predetermined?

to the extent that classical mechanics and the completeness of your information allows - i.e not very far!

Does it have to do with special relativity and light cones?

no

2. Please explain eternalism and block universe in simple terms. Sorry I was always dumb and I am unable to understand this.

it seems to be about perception and interpretation of time and nothing much to do with the mechanics of the universe.

3. Is our 4D universe flat and exist on the surface of 5D hypersphere? Is the hypersphere expanding?

if that's how you want to model it, and your model is explanatory and accurately predictive, stick with it.

4. Is it really impossible to see the present of a distant planet?

obviously what you see is what happened when the light was emitted. 

Could some abstract higher dimensional perspective(eg. God/programmer) see all of simultaneously existing time since 3D beings can only see time as being very subjective? Are we even 3D?

Very confused thinking here. Time is what separates sequential events. If you can distinguish between before and after, you have a consistent timeline. An omnipotent being with fairly unlimited patience could unscramble an egg, but why would he have scrambled it in the first place?   

[evan_au]

2. Please explain eternalism and block universe in simple terms. Sorry I was always dumb and I am unable to understand this.

Don't feel too bad about it - this is beyond what we currently know, and all we have to work with are hypotheses rather than evidence.

The Block Universe is a hypothesis coming from the direction of Einstein's relativity.
The Many-Worlds hypothesis comes at the same question from the direction of quantum theory and Schroedinger's equation.
Which one is true (or both, or neither) is currently unknown.

As I see it, the Block Universe at least provides a mental model for 4D spacetime.
- It is hard to imagine a 4-Dimensional object when all our experience is 3D
- But I have seen the Block Universe concept used to compress the hard-to-imagine 4D down to 3D which is easier to picture in more concrete terms.
- For example, it is hard to imagine the orbit of a planet in 4D spacetime= 3D space + 1D time.
- However, by taking a slice of space in the orbital plane of a planet = 2D space you compress 3D space down to 2D space
- By adding in time, you change to 3D spacetime = 2D space + 1D time
- So we can imagine the circular orbit of a planet in 3D space
- and we can then picture the same planet taking the path of a spiral along the time axis in 3D spacetime. 

See: https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time)

[Halc]

How can past, present and future exist all at once?

By a definition of 'all at once' that is different from 'all at the same time'.  The phrasing you use for that is considered correct, but the reference to past, present, and future belongs to a different interpretation. There is no past, present or future in a block interpretation. Past and future (and ambiguous) are just relations between pairs of events, none of which is 'the present'.

Many light years away, alien lifeforms would still be seeing dinosaurs on earth since only dinosaur earth light has had time to reach alien lifeforms so far, but how can earth's future be seen?

Again, there are no events that are 'the future', and confusing statements will always seem to arise whenever you phrase a question in terms that assume a presentist view, so best not to.  The year 2021 can be seen by humans that live then.  The dinosaurs cannot because there are no humans at the same time as them.

How is future also predetermined?

There is no 'the future'.
The state of any particular point in time is not necessarily determined by prior events. Much depends on the interpretation of QM used. I for one don't buy into determinism, but there are interpretations that do. If it is determined, then the future of any given event (say the next-year future of Earth, 1950) is completely determined by the laws of physics, which cannot involve true randomness, else it wouldn't be deterministic.

Determinism or not has nothing to do with the presentist/etermalist interpretations of time, since either interpretation of time can be paired with deterministic or non-deterministic physics.

Does it have to do with special relativity and light cones?

Not really. It (and the principle of locality) has to do with quantum mechanics.  SR (notably the principle of relativity) contribute to the suggestion of the block interpretation of time since for any given event, if that event is objectively 'the present', then multiple distant events can be simultaneous with the one event depending on the frame of reference of choice (see Andromeda paradox), and hence either none of those distant events is 'the present' (contradicting presentism), or only one of the frames of references is the correct one (contradicting the principle of relativity on which SR rests).  Hence SR suggests a block view.

[Halc]

2. Please explain eternalism and block universe in simple terms. Sorry I was always dumb and I am unable to understand this.

Simply that all events have equal ontological status. No slice of time is the preferred 'present', and lacking this preferred moment, the preferred moment cannot move, so time isn't something that flows. Thus any coherent discussion of a block view must avoid references to the present that doesn't exist, or else the statement will make no sense. You cannot mix the two views.

3. Is our 4D universe flat and exist on the surface of 5D hypersphere? Is the hypersphere expanding?

This does not seem to be the prevailing view, and is not the eternalist stance. An expanding hypersphere as you describe seems to add a 4th spatial dimension (to get 5D from 4D) and a second dimension of time (to give it time to expand).  A block universe cannot be 'doing' anything since time is intrinsic to it. The block universe is not an object existing in time, as that would be a second kind of time.

4. Is it really impossible to see the present of a distant planet?

Under block universe, there is no present, here or on the other planet. We need to reword the question.
So is it possible to see an event on the distant planet that is simultaneous with the viewing event here on Earth? No, the finite speed of light forbids that. We could send messages faster than light, which is impossible.

Could some abstract higher dimensional perspective(eg. God/programmer) see all of simultaneously existing time since 3D beings can only see time as being very subjective?

Under a block view, we're 4D beings, having length, width, height, and duration. Light does not 'exit' the universe, so if there is something external to the universe considering it, 'seeing' would be the wrong word to use since light (information of any kind) does not go from anywhere to this external point. Yes, the structure could be considered mathematically, and if it is hard-deterministic, all the states could be known if the initial condition was known.

[yor_on]

I don't know, nobody does. I still will try to define it. It's 'energy',  and 'energy' is a coin of exchange. the way it works is called 'entropy' From that we go to relativity in where the only thing we can define is your local model. If that agrees with mine and others, we have a 'fact'. The same goes for any 'repeatable' experiments you create.
=

It's about building a world image. In relativity all models are local, they build up to a 'global' model in where we state this will be valid for all times, and at all places. In quantum theory that's not enough. that's where 'many worlds' come in

Block universes comes in various shades. The thing joining them is the idea of 'time' not having a arrow. And free will may exist or not in such a universe. As long as we define the choices as being 'infinite' in it.