Kurzgesagt (In a Nutshell)

Some of you are going to die, but that's a sacrifice I'm willing to make. Go on my cells, for the sick tattoo.

The video sure goes out of its way to make tattooing look as gruesome as possible.

If I ever thought I might want a tattoo… well, not anymore

Though really, the worst part was seeing the needle in action.

I think we've got a few new needlephobes after this video, yeah.

Image?

Just watch the video, you'll see.

On a logarithmic scale, we are exactly in the middle of the smallest and biggest thing we can observe.

Is this weird? I'm not sure.

I remember contemplating that when I first learnt planks constant.

I really appreciated seeing the comparisons of scale for things inside our body compared to us inside cities, countries and the earth. Was surprised to hear for some bacteria on our skin we are the equivalent to the earth in scale.

Hearing that the milky way is comparatively only a day's commute away from the edge of currently observable space also greatly interested me, made me wish he had more exploration of size comparisons between cosmic sizes.

Note that "crossing the visible universe in a day" would be 12 orders of magnitude over the speed of light, at about three billion lightyears per hour, and equivalent to travelling 500 km in a day.

Edited by Redmess on Dec 17th 2023 at 1:35:38 PM

Oh there's true, if you were the scale of a galaxy, the maximum speed of things would seem very slow.

Edit: 500km? So if the scale of the universe was shrank down so that a galaxy was as big as a person, the observable universe would be the size of Germany?

Edit 2: took me a moment to remember that space is three dimensional so the observable universe's 200 billion galaxies are going to be far more spread out than Germany's 80 million people.

Edited by Whowho on Dec 17th 2023 at 3:50:03 AM

I don't like the fact that they're ignoring a couple of very obvious concepts:

• It's not a single spacetime continuum that's predetermined, but rather an infinitely branching "tree"/"web".
• This spacetime continuum-tree acts more like a blueprint for what can happen, and the universe just happens to traverse a specific path through this tree based on the random "choices" made through quantum physics (e.g. whether a radioactive atom decays the next moment or not).
• The many-worlds interpretation (i.e. multiverse theory) would make it so that there are multiple pasts, presents and and futures that coexist together, and so even if relativity-based tricks like the one shown in the video can allow someone from a given present to communicate with a given future, it's perfectly possible for said present to take a path that leads to a different future altogether that technically makes that aforementioned communication impossible (e.g. the one you communciated with in the first future is dead at that specific time in the second future).

That said, this "block of spacetime" model does basically provide a scientific explanation for all the fictional stories where people can communicate in real time with other people in the past/future from the first group's present. I wonder how would a universe reach an end in this case? The explanation would entail that the universe would be simultaneously newborn, mature, and had reached its heat death.

Edited by MarqFJA on Jan 31st 2024 at 6:25:01 PM

Iirc things at lightspeed are thought to experience all of time?

PBS Space Time covers this topic in a couple of videos, the most applicable being here:

In a nutshell (snrk), general relativity demands that there is no such thing as a consistent "now". Our perception of time depends on our perspective in space — it is relative.

However, we can construct a logically consistent sequence of events based on the progression of causality. You and I, travelling at significantly different velocities and/or light-years away from each other, may disagree on the elapsed time between any two events, but we will always agree on the sequence.

In both Newtonian and general relativity, the universe is perfectly deterministic. A single slice of it at any given moment in time can be traced backwards to the infinite past and forwards into the infinite future, but there is no privileged point of view that would allow one to identify a present ("now") that all observers would agree upon.

Each of us in this conversation, on the same planet and a mere few thousand kilometers apart, is out of sync with each other by microseconds because of the time it takes information to travel between us.

Quantum mechanics introduces some problems with this concept if you accept the interpretation that the outcome of every event is fundamentally random. It should, in principle, be impossible to predict the future, but you could always reconstruct the past by tracing backwards from the quantum information embedded in the present.

In special and general relativity, massless particles move at the fastest possible speed and experience zero time. From the perspective of a photon, its entire existence is instantaneous even if it travels from one end of the universe to the other.

Edited by Fighteer on Jan 31st 2024 at 11:41:27 AM

The block of spacetime seems to be the simplest explanation that satisfies most conditions, at least. Occam's razor applies here, too.

Yeah, that's a major part of this video, and the impetus for modifying the block model by only applying it to the past, with the present being a thin film upon the "top" of this block that has a highly uneven surface due to the variable speeds of the universe's objects. As the present progresses through time, the block grows and pushes the present further up.

They do also mention that there are many other possible models of time that compete with the block model, or at least parts of it.

Edited by MarqFJA on Jan 31st 2024 at 3:52:18 PM

There are also models of quantum mechanics (Many Worlds + decoherence, Boehmian) that allow for a deterministic future.

I suppose the many-worlds model could be considered deterministic if you assume that worlds that are identical up to the point where they diverge coexist with each other, rather than being literally a single world right up to that divergence point.

It would still be deterministic on a multiversal global level, it just wouldn't be for individual universes. If all options have their own universe, then any given string of options will have a deterministic path in one universe.

many worlds does sorta feel more philosophical than really scientific in a way?

It is, as far as anything I've seen suggests, unfalsifiable, which is one criterium that can make something count as unscientific.

Edited by ShinyCottonCandy on Feb 1st 2024 at 9:47:38 AM

As with any scientific theory, the crucial question is whether it can make unique, testable predictions. If Many Worlds and Copenhagen always produce identical results in experiments, then there's no way to prefer one over the other and they're both equally valid interpretations.

Quantum mechanics is one of the more fascinating areas of study because the realm it examines is uncertain — literally. It's not that there's some hypothetical improved instrumentation that would allow us to see better into its depths. We are studying uncertainty itself and attempting to quantify it according to definite rules.

The version that seems most reasonable to me is quantum decoherence, which suggests that there is never any "waveform collapse", as in Copenhagen, but rather that the macroscopic outcome of any quantum interaction is the sum of all involved probability waveforms. Waveforms that interfere constructively (coherence) dominate the result. (Even that is a bit of an oversimplification.)

To suggest that any of these ideas are "unscientific", however, is a gross misunderstanding. The equations of quantum mechanics have been verified to the highest precision of any experimental results ever achieved by mankind. We're talking things like the fine structure constant, the mass of the electron, etc.

There's zero doubt that the quantum mechanical view of our universe is correct. It's just incomplete.

Edited by Fighteer on Feb 1st 2024 at 10:15:38 AM

You know, reading up on the subject of determinism versus free will as an extension of this conversation, I've come across not only compatibilism (i.e. the idea that the two concepts are in fact compatible with one another), but also the notion held by compatibilists that both metaphysical libertarians (who assert that determinism is false and free will is possible) and hard determinists (who assert that determinism is true and free will is impossible) are caught up in a false dilemma. What are your thoughts on this?

Edited by MarqFJA on Feb 1st 2024 at 3:40:47 PM

At the risk of going on a philosophy derail, I see nothing in any mainstream scientific theory to suggest that free will exists in the most extreme sense: some kind of decision-making entity that operates outside of physical causality.

As much as I'd like to believe that the things I think and do operate from some kind of "uncaused cause", I don't think that's likely to turn out to be true.

There is room for some other, narrower concepts of free will to exist, however. If Copenhagen is correct, then the universe is an enormous random number generator at its most fundamental level, and so everything we do has some probabilistic element to it. Unpredictability is a kind of freedom, so there's that.

Another way to look at it is that we will probably never be able to fully see under the hood to calculate every outcome of every quantum event perfectly, even if our theories might in principle allow it. Thus, whether the universe is perfectly deterministic or not, unpredictable things will still happen.

Edited by Fighteer on Feb 1st 2024 at 7:57:37 AM

FWIW, ancient Chinese philosophy/religion subscribes to a dualistic model where a human has both an "ethereal" soul that leaves the body upon death and a "physical" soul that remains in the corpse, and Islam seems to subtly follow a similar approach with the frequent distinction between the rūḥ (the divine spirit/breath of life) and the nafs (the psyche/self that dictates one's "disposition"/"characteristics"). Even if a soul does exist (which I personally believe) and it's technically outside of the physical world's system of causality in itself, it could very well be that it has to open itself to being at least significantly influenced by said physical causality in order to interact with the universe through the body that it's attached to (which in itself may be mainly about subtly nudging some of the quantum-level probabilities that ultimately underly cognitive processes), hence why alterations/damage to the brain's structure/biochemistry can cause lasting changes to one's personality for example.

Just throwing that out there in hopes that it may help you with reconciling what you desire with what science tells us.

Here's another dose of scientifically researched nightmare fuel.