DanMP

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".

OK, thank you!

I knew that you would say that. We probably can't. So, the age of the universe was not "converted" to "today time" on Earth. Still, there may be an unaccounted "gravitational" redshift, because the "ancient" light originates from a denser region than we have now, here.

Yes, good point. Still, the universe was much denser than today. Comoving with what? Also, where, on Earth surface, between galaxies or on a neutron star "surface" 😀? Keep in mind that the Earth was not there in the beginning, nor any neutron star, nor the current intergalactic space, which is almost empty now. We shouldn't neglect gravitational time dilation, nor gravitational redshift. Probably they didn't, but I'm not sure. Slower than our clocks, situated on Earth today.

I understand what you mean (I am also "redshifted" 😛), but still, this forum is much better than physicsforums, where the moderators are very quick to close the topic, or restrict your right to write in it, when you insist asking uncomfortable questions. Just search/see my activity there. They are like a Physics Inquisition. This is not the case here. Regarding this thread, I believe that your misconception was to consider the balloon analogy with the Earth in the center ... Consider the Earth as another point on the surface of the inflating balloon and you will understand the responses you get. I also have some questions and observations regarding big bang theory: When they assessed the time from big bang, what reference frame they used? There is no absolute time. Just after big bang, the mass was confined in a small volume, yes? We know from GR that the clocks are slower when they are situated in/near a place with high density. Also light originating from such a place would be redshifted. Was this redshift considered (subtracted) when the speed of expansion was calculated? Last but not least:

You have to ask RossJ what exactly he meant. I think (but I'm not sure) that by isolation in time he meant that in the nucleus time may be dilated (gravitational time dilation). Such a thing may partially explain: To be honest I don't agree with most of what he wrote, but I intended to be positive.

Interesting idea. I thought about something similar many times. Anyway, you may want to read about the Thorium Nuclear clock project.

In OP, wei guo wrote about many issues: dark matter, dark energy, "extra position", extra dimensions and "extra parallel reality". Most of you cherry picked the "extra position: superposition" error and ignored the issues of introducing: extra dimensions, parallel universes and dark energy. They are distorting the instinct of reality as Wei Guo said. Do we really have evidence for extra dimensions and/or parallel universes? Why such things are accepted in mainstream physics? About dark matter I disagree with Wei Guo, but for the rest I'm not. There are real issues. About "extra position: superposition" error, yes it was an error, but I guess that he/she was thinking about things like the explanation for interference of individual particles in the double-slit experiment, where we consider the particle taking more paths in the same time, as if the particle can be present in more than one position at a time. I don't agree with such explanations either (I have another one, more intuitive). yes

Well, I'm not really interested in this alien theme/subject and it seems that neither are you, because if you were, you would know about ancient aliens/astronauts theory, also that an alien civilization may be much older/advanced than ours, that a probe may stay hidden long long time, and so on. I wrote about this subject mostly because I hoped that someone interested in it, and talented, would be inspired by my ideas and write nice SF novels or movie scenarios. I don't know about you, but I decided to let others take over, if they want/need to. For me it's enough.

No, I meant around us ... Another reason to have more alien probes, with different agendas, here.

0.1c with the technology that we can have or imagine today ... Even so, I wrote "under 100 light years", not 100 or over. If the distance is around 20 LY we can get info from the probe in 2-3 centuries. I also wrote about other ways to get new info + other reasons to send new probes. And there may be more than one civilization around ...

Well, if the target is not very far (under 100 light years), new data may be collected in few decades/centuries, both by the first probe and/or by new/enhanced telescopes, or new data may arise due to the developments in the targeted planet (first EM emissions and/or other activities, like atomic explosions, artificial satellites, etc.). Other reasons to send new probes may be: the technology needed becomes less expensive the new senders are not happy with the others agenda the enhanced technologies offer new, much better, approaches/possibilities (see here how I would do it) Anyway, If they are Bracewell probes, we shouldn't care. Just wait for them to contact us, when they consider appropriate. If they are, instead, alien probes sent to spy us prior to a future invasion, we need to properly investigate all the sightings and also to prepare a defense, although our nuclear arsenals may deter such plans, because on arrival they may find here a destroyed, uninhabitable planet ...

Maybe, but not necessarily. The Americans, Russians and Chinese are not getting along very well and have different space programs/projects ... And we are talking about centuries from now ... and maybe more civilizations ... So one planet may have dozens/hundreds different visiting probes. A Bracewell probe may delay the contact "until we achieve a certain level" (my option 1) or just be "afraid" of us (my option 2) and abort it. If option 3 is the one, then the probe is not a Bracewell probe, yes, but we shouldn't ignore that possibility.

We can use nukes + railguns: There may be another way to "save"/cool the Earth: large sheets of reflective materials on orbit around the Earth, both for shading & cooling the hot regions (including storm cells) and for heating the cold regions (by reflecting sun light). Besides tempering the climate, electric energy can be saved (less power used for cooling/heating) and produced (solar panels on Earth using the reflected - and focused - light from orbit). No fusion reactors needed ... Just railguns and/or nukes to launch the materials on orbit and astronauts/robots to deploy the sheets. Not easy but doable.

I realized that "caused by aliens, but not as part of some official mission" + "The officials would rather chase away those intruders" is also true, and more probable, with long/normal travelling times. The probes, equipped with AI, may be sent by many different organizations/nations in many "waves"/years, with quite different technologies and agendas, resulting in apparently chaotic behavior of "the aliens". We, from Earth, will probably send, in the next 100-200 years, dozens or even hundreds of such probes to the nearest interesting solar systems, and we already have many different nations and organizations involved in space exploration ... And, if there are such alien probes here, they may be reluctant to contact us because: they don't want to interfere in our development, until we achieve a certain level or they are afraid that we may attack their home planet if we learn about it/them or they don't want us to be prepared when their invading fleet would arrive ...

No, I don't think that an alien civilization capable to reach our planet would be incapable to make contact with us. Not willing maybe, yet. So, the UAP/UFO phenomena are: natural phenomena, not fully/satisfactorily explained caused by humans on purpose (practical joke, illusionism, etc.) or by accident (secret technology) caused by aliens, but not as part of some official mission. If an alien civilization has achieved (although it's very improbable!) the technology for fast and not very expensive space travel, fast enough to make a trip to another planet and back in days/weeks, or the technology to jump back/forward in time or to jump to parallel universes and back (I personally don't buy/believe such things), it would be possible for private alien citizens to briefly visit us, just for fun. Official missions won't be so sloppy ... The officials would rather chase away those intruders.

Yes Sabine kind of slipped a cog. I watched her video (I am subscribed) and I see that she became more interested in gaining views than in being logical. With that title, and the ambiguity, she definitely gained a lot of views ... What she missed? 1. She based her arguments on a theory (GR) she considered (in the end of the video) in order to be replaced with a new one, quantum gravity, making her arguments more or less irrelevant. 2. She missed the fact that the speed of interaction is also c, so if you move faster than c, you would normally brake apart.

Ok, even if they "solved the distance problem by harnessing a physical principle that human beings have yet to actualize" (which is highly improbable), there are plenty of planets to visit, so the probability to be here, now, should be much lower than you think. Another problem: if somehow aliens arrived here, what are they doing? Would you do such an effort just to play hide and seek? Apart from UFO being misinterpreted natural phenomenons, there may be also other explanations, like secret military research/experiments, including genetic (see the creature in Brazil; it reminds me of Jurassic park).

Since not everyone is familiar with that, they might arrive at a different explanation. Same with Iridescent Pileus Clouds.