DanMP

Who would? You? Autonomous robots to work for us is not a bad idea, especially when AI will be 1, able to control/maintain fusion (I recently read something about that), in order to have plenty and cheap energy, and 2, able to safely control such a robot.

I was sure that you will say that 😀 and I may offer other examples, like swimming in the ocean or spacewalking, but you can say that the ocean is an object and the spacesuit is also required. So, yes, we need objects. We are, also, objects 😀 Still, the fact that we need objects in order to see/experience space, doesn't change the fact that we see/observe changes/events not the time dimension, nor the fact that time dimension is different, as I explained before (you can't stop or go back in time). It's not a problem, because we can (and did) make clocks, devices that count repetitive events, so we have more than our subjective perception. I think that this discussion about the perception of time and space should be separated from the thread, because it is no longer on topic.

OK, thank you for all your answers and for your patience. Thank you! I prefer the second one.

Yes, I understood your point, and it's a good one ... in understanding time. Not in seeing it. Swansont agreed that time is something we cannot see, touch, feel in any way: My point was/is that we observe/see change (in fact the succession of changes/events), and from that we understand that it must be something somehow similar with a spatial dimension, something that we call time. But, as I said, time is not quite similar with space dimensions, because you can't go back in time or stop in it (stop your advance in time, ageing). Not absolutely. A blind man can sense space just by walking in all directions. He can even measure distances, by counting his steps.

You are talking about the theoretical/abstract model. I am asking about how the mass actually does that.

I fixed it: The question was, see above, how the mass can change "the curvature of spacetime" in my proximity? Can you answer this question please?

Maybe, but your answer is not. The strike line was unintentional. I try to correct it.

Because Earth or other body you mention are far away and your ship cannot be affected directly by them without "an action at a distance." What it can be affected by directly is the geometry of spacetime Who said that my ship has to be directly affected by the incoming mass? I wrote: The question was, see above, how the mass can change "the curvature of spacetime" in my proximity?

In the case of the Earth approaching my spaceship location, yes, you can do that. But remember that you wrote: so we can replace the Earth in the scenario with a huge spaceship, arriving near my location (much closer than the Earth would do) by using its thrusters (not in "free fall"). Again: You would stil "blame" the affected geometry or some other geometry? Why? And I repeat the question:

I can sense the space my moving freely through it. In fact objects are not always good because they can block me (I can't really sense the space from a coffin 🙂). On the other hand, in order to see its expanse, yes, objects, like stars, are very useful. Also meter sticks are good/needed to measure lengths. Yes, the change of doors, from open to close, can stop/block me from moving through space, but there is no real temporal obstacle, I cannot stop/block your advance in time using objects (or any thing that I can imagine). This is another major difference for time (compared to space dimensions), besides the impossibility to go back. This is very similar to what I wrote in my first post here. What you can see/observe is change, but this allows you to define a time dimension. More about my opinion regarding time is here.

Yes, but there is always a mass (or energy) required ... The geometry doesn't change without a change in mass/energy. So I would "blame" the approaching mass, not the geometry that is affected by it.

You can see me changing from walking to jumping. You can't see the "expanse" of time as you can see the expanse of space. It seems to me we move exactly like that Ok, so move back in time as you move back in space

And what is wrong with 3? The changes mentioned in 1 and 2 only occur when the Earth is approaching ... Why are you discounting the Earth as a cause?

We can directly observe space dimensions by moving (walking, jumping) in all directions (as long as there is no obstacle to prevent it), but in time we cannot move like that, and the only thing (regarding time) we can directly observe, is change. We see the sunrises/sunsets and we consider that a day passed between two of them, we count the oscillations of a pendulum and calculate how many hours, minutes and seconds passed, and so on. But the observables are the events we count (and the changes in and around us), not time itself. Back on topic: I wrote that the mind is the result/product of brain activity, and that the observable is the brain, not the mind. Now I want/need to add that the mind is in fact observable, but only from inside

When I wrote "local" I meant "in the proximity". Let's consider a simple example: I am on a spaceship hovering somewhere on the Earth's orbit around the Sun, not exactly on collision course , but 1 million km closer to the Sun (at 148.6 million km from the Sun, when the Earth is at 149.6). Most of the time/year, in order to stay at that fixed point, I have to use the propulsion to compensate the Sun's "gravitational pull". Once a year, when the Earth is near, I have to orient the ship thrusters towards the Earth, not the Sun, in order to maintain my fixed position in Sun's reference frame. The question is: why I have yo do it? because of gravitational time dilation changes? because of spacetime curvature changes? or because the presence of Earth (more exactly its mass) is changing "the curvature of spacetime" in my proximity? Another question is how exactly the Earth does that?

Ok, it sounds interesting, for a fantasy movie or book, but this is a science forum, so some evidence are needed. There are any?

Maybe, but the curvature depends on the local mass and/or energy ... You remove the mass/energy and the gravity is gone.

Length is as observable/measurable as time intervals. But time as a dimension is not as real/observable as the space. Time is a (very) useful concept but is just a concept, like the mind. The real/observable "source" of the mind is the brain and for the time the change.

Time as duration/interval is observable/measurable, yes, although a clock is just counting events, but time as a dimension is not really observable. As I wrote, what we observe is change.

So the curvature has no cause?

Time dilation is the "dominating effect" or the dominating [apparent] cause? I wrote apparent because, in my opinion, the actual cause of gravity is the one that creates "the curvature" ...

Time is observable? Should we dismiss it? 🙂 What/who is a physicalist? The place where "thoughts, inner images, the inner voice, dreams, and experiences reside" is the brain. And it is something physical, biological, observable, not at all a non-physical dimension. If you really want, you can consider the mind as the "dimension" you described. But the mind is the "product" of the brain, something observable. As time is inferred from the fact that we observe change.

Not all. An extra scattering and absorption due to higher interstellar gas density would decrease luminosity of the source in any scenario. How was this addressed?

Long time ago I was thinking about a method to subject athletes to higher gravity in order to increase their performance. I imagined special suits in which I would add half a kilogram (sand or something) each day until they double their weight. The extra weight must be evenly distributed and they should wear the suit all the time, so the idea is not very practical. Maybe a space station with artificial (centrifugal) gravity would be, one day, used to increase athletes performance by increasing gravity.

I didn't check but I agreed that Friedmann equations would account for increased redshift due to higher density back than. Still, there are other possible issues due to that higher density: more matter (mostly hydrogen) between stars/galaxies would absorb and/or scatter more light, decreasing the luminosity and making the source to appear farther ... It is very obvious, so I expect to be accounted for, but how? Another thing, nobody commented about the video I posted: the new estimation of the age of the universe and the possibility that part of the redshift may be from "tired light". I wonder if the late would also account for the increased expansion caused(?) by "dark energy".