Spacetime

Okabe Rintarou

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no i said that past, present , future all exist and are equally real and passage of time is merely an illusion .I never said time is traversable or not. It's not that what i want but what we get from relativity of simultaneity.

In the Lorentz transformation animation below, with time on the y, space on x, and the large “X” as invariant light speed, you can see how events (moments in space, depicted here as dots) sometimes move from past to future, when the observer travels away from this direction at relativistic speeds.

View attachment 78400

another depiction.
View attachment 78401

So, if we assume the past is gone and the future non-existent, with a fundamental “flow of time” (with a “speed of time” relative to what exactly, as “speed” already has the unit of time in it?) then we have to find this “absolute 3D now” that every moving body must agree upon, in order to define which parts of spacetime are either already gone or still non-existent.

And this has been revealed to be absolutely impossible
, as simultaneity has shown to be a completely relative convention of ours. Everyone has another opposing “real moment”. My now can be included in your now, while your now is not within in my now, but in my past or future, because of our relative motion towards each other.

This is why this has become such a prominent interpretation among physicists, even if it goes against things we are commonly strongly attached to, such as a very strong early intuition, our sense of free will and, for some, religion.

Prof Brian Greene video on it .

This reply and especially that video, feel like a regression in our discussion. We've already discussed the spacetime interval. Our understanding of the present does indeed depend on our velocity, so while my perception of the present tells me that my Sun (Surya) has not entered the CNO cycle yet, in the perception of the present of an Alien (who is, according to me, part of my present and travelling towards me in a Kugelblitz drive powered spaceship), Surya has already entered the Red Giant phase and is getting most of its energy from the CNO cycle, as I've already said in post #10. So in that sense, time is indeed subjective. But in Minkowski spacetime, you don't look at time nor space, rather you look at the spacetime interval, as an objective measure.


Minkowski spacetime doesn’t actually say we are moving through time at any speed. It merely reveals intervals between spacetime events.

A particle’s own distances in time does not mean it has a speed, there. The ‘c’ in the spacetime interval s=x2+y2+z2−(ct)2−−−−−−−−−−−−−−−−√s=x2+y2+z2−(ct)2 is just a number used as an exchange rate between our units for time and distances. Like 5280 feet per mile. So c is not a speed, but a constant (that's what that c stands for).

Also, the c is not there when we’re using Natural units - Wikipedia.

Spacetime is unified into one, single continuum, so time should not be seen as separate from space.

Minkowski spacetime represents a 4D picture of events. Nothing is moving in a picture. You are an unchanging 4D body in Minkowski spacetime.

View attachment 78398

So, as soon as you imagine 4D objects in Minkowski diagrams to actually represent 3D bodies going through time at a certain speed, much in the way your 3D car could be driving through space, you are confusing yourself.

The flow of time that we all consciously experience in any moment, where things are clearly changing all the time and always from the past towards the future direction are all phenomena that stop as soon as very specific parts of our brains stop functioning.

In other words, the experience of flow is not fundamental to physical time itself, but a result of our complex biology.

This GIF can manipulate the visual memory parts that are responsible for the experience of visual change. It will show you that things can appear to move when there’s really nothing moving “out there”:
:



These brain parts we’ve manipulated here, are also responsible for adding the sense of visual change to the currently observed location(!) of, say, a moving car.

There are people that have these visual memory parts damaged. These people are only capable of seeing the current picture of the present moment, but the hallucination part of motion doesn’t work at all. They’re known for seeing flowing water as a glacier and aren’t capable of noticing if something is approaching them or not. This condition is called Gross akinetopsia - Wikipedia.

Now, if you really were a 3D body moving through time at some speed, very much like that car moving through space with a certain speed, you would be able to observe more than a single moment of it, would you agree? You would watch a whole “time scenery” pass by, much like watching the spatial scenery pass by in the car, right?

We might intuitively believe that we do, but imagine you could change into me, from one moment to the next. And I mean me, atom-to-atom. Would you notice the sudden change as part of this “time scenery”?

No, you wouldn’t, because all of those memories that are stored inside me, inside this physical moment, will be adopted too.

It will feel as though you were me all along. So that sense of me-through-time is biological, not fundamental to physical time itself. Every moment is really very isolated from the previous and the next, no matter how much they influence each other.

Say that you became me, atom-to-atom, at the very instant I put down my cup of tea, right at that moment it hit the table. At this particular instant (that, in this case, doesn’t have an actual, physical neighboring past moment “as me” at all) you are experiencing one infinitely small, isolated moment, that included a little visual memory of me also putting down the cup.

It includes this memory as the experience of actual motion towards putting it down.

That part of experienced motion is memory that doesn’t feel like memory at all. It’s a type of hallucination that feels like it’s actual, clear reality happening right in front of you. But a hallucination based on something that actually exists inside the inaccessible previous moment (that we can only assume to be there).

So this biological sense of flow cannot be said to go at any speed, because the observed change inside the moment is illusory.


I copy pasted it from other site. as it's easy to understand this way.
I still disagree.
  • You say that we humans are 4 Dimensional creatures and that its our Biology that makes us experience our 4D existence as a 3D slice changing with time, which you therefore call an illusion. But that doesn't explain the experience of non-living things. The surface of the Moon has information about the impact of various asteroid and meteorite strikes on it. The distribution is rather random, and if you change the initial condition of the Solar System just a little bit, the distribution changes drastically into another random pattern due to the Butterfly effect. So take our Moon and reverse the Arrow of Time, the degree of randomness and quantum of information on the Moon's surface begin to decrease! Spontaneously! This means that information that exists in the Universe is being erased. The law of conservation of quantum information suggests that this should not be possible. Goes to show that time indeed flows in only one direction.
  • Gross akinetopsia is a condition that only affects the visual cortex of the brain. So the patient can still hear touch and smell in a normal manner. So your argument that we stop perciving ourselves as 3D beings and become 4D beings when certain parts of our brain stop working is drivel.
  • Now let me say that with a fresh perspective: A being that is 4 Dimensional and conscious of it might sense the entire 4D block universe and would look at the lives lived by us 3D beings as a 4D object. But even now, that 4 Dimensional being is only perceiving one world line. What about the countless others? And this is where your assumption collapses. If time is but an illusion and we are just 4D creatures, then it would follow that only one world line exists, that only one world line is real. So tell me, based on what law is it decided at every point in the 4D universe which world line we are?

Let me conclude with this: Entropy and the arrow of time arise from basic statistical mechanics. Not Biology. There is no denying that time does indeed flow, even if its flow is subjective. Here is a simple, yet rather atypical explanation of this concept:-

Qstn is can we ever do time travel ?
As I understand it, time travel is sort of possible, but we are limited in our choices. So we could create a twin paradox, but not a Grandfather paradox. We can't freely traverse time as in most movies. Nor can we use time travel to violate the Law of Causality. But we can lengthen our lifespan in Earth Years if we take a fast spaceship and travel around and return to Earth after sufficient time spent traveling. We could leave in 2022 and while in our time the year we get back is 2030, in Earth time, the year might be 2035.
 

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