If there are experiments that can be tried to challenge my own current perspective on the matter, I’m interested.
Because to my mind, anything that is said to emerge implies that the dimension we usually refer to as time is already an implicit hypothesis of this anything being able to emerge.
And if there is something out of time, then by its very definition it can’t interact with time:
- either there’s a connection with time and then at some point there is a change to that thing that can no longer be considered an absolute static thing as there is a before and after event that this thing is attached to,
- or this thing is without any relation to time and thus can not be something that engender time itself.
To be clear, I think there is still large room for interpretation anywhere formal mathematical means can give us great insights that would be unreachable without them. Agreeing with equations is not agreeing on the interpretation to give to the equations at a larger epistemological picture, and even less on ontological genesis.
The bits of a movie on a DVD depict regions of space evolving over time. The DVD and its bits exist in space and time but they are static and the spatial arrangement of the bits is pretty much unrelated to the space depicted by the movie. If you had sufficiently good eyes and mental DVD decoding capabilities, you could look at the DVD and get a God's eye view of the world, see all of space and time at once, at least the parts captured in the movie.
Similarly in a computer game, to run into a wall does not require the player and the wall to be next to each other in any real sense, it is sufficient that some code knows which memory locations to inspect to detect a collision and constrain the motion accordingly. Similarly running into a wall in the real world does not require that you are next to the wall in some fundamental sense, the universe could at a very deep level just be a list of object coordinates and the laws of nature would cause a force whenever two coordinates become very close.
I will agree with you that it is much harder to think of time in a similar way but I am willing to consider this potentially a limitation of human brains. From Einstein we know about the close relationship between space and time and I can relatively easily make sense of the idea that spatial relationships are not fundamental, so maybe that just carries over to time, even though my brain can not make sense of it.
This is one take on what Bohm called the implicate order, and which is implied in non-locality and superdeterminism.
Reality is a projection of a hidden system which operates under completely different rules.
And when we get down to the quantum level, we start seeing that essential information is somewhere else.
You can't look at a single electron and see that it's entangled. So where does the entanglement information live? It's clearly not inside the electron. Is a measurement really an interaction with the projection mechanism?
This sounds like simulation theory, but it doesn't have to be. There might be a super-causal system of relationships and meta-objects without needing a "computer" made by a conscious entity to keep track of their relationships.
There are no such things as absolute static things in relativity theory. "Before" and "After" depend entirely on the observer. Energy/matter and spacetime are deeply connected through the Einstein equations, so much so that they may indeed be "the same underlying thing".
Approximate static time and space are convenient illusions/approximations, that happen to be very useful for us as a species when it comes to surviving and replicating, but the Universe has no obligation to cater to our feeble minds or senses when it comes to reality.
> "Before" and "After" depend entirely on the observer.
This is only true for space-like separated events. But the earth gets wet After the rain started, for any observer in any frame of reference whatsoever. The eggs have to break Before you can make the omelette.
I feel like someone could describe foam emerging from the sea without implying that it is a process in time. It could be thought of as a process relating to the properties of seawater, wave agitation, sand etc. It is possible for a picture, not a video, to depict foam emerging from the sea. Also, there need not be a before or after, or even quantifiable extrinsic changes.
Consider an unchanging singly-linked list as a universe. Time (or perhaps "the passage of time") in the intuitive sense does not exist for this universe, but it does exist in the sense that there is a global ordering of values. But does the ordering of the values come from the edges or the nodes? The ordering requires both.
Or, more humanly(?), a film reel.
At least, this is how I would think of it if required to give a simple-but-possibly-off-base answer for a possible way time could be emergent (would love it if someone more educated could correct me). This is also known as the Einstein block universe model.
Otherwise, since my physics education is far below the actual bar needed to understand quantum gravity stuff, I think back to thermodynamic microstates and macrostates, and how temperature is emergent.
You can have time without having time - block time
https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time...
Just in passing, Quanta magazine has been excellent lately!
It was also excellent in the past!
It's excellent in general
Does anyone have a good recommendation for an introductory book on these concepts?
I read a bit of The Fabric of Reality but had trouble progressing too far with that one. The author talks about the quantum slit experiment, somehow arrives at the explanation of parallel universes, and then claims anyone who disagrees with this conclusion must have faulty logic. A huge chunk of reasoning behind parallel universes seems to be skipped and I have trouble taking it seriously every time it is brought up.
You might check out the PBS Spacetime series on YouTube. https://www.youtube.com/@pbsspacetime
It seems to be well produced but the presenter rubs me the wrong way for some reason.
For German speakers, I also recommend Josef Gaßner's YouTube series "Von Aristoteles zur Stringtheorie" (I find it a bit more structured than PBS Space Time, albeit maybe less amusing).
I love watching this channel even though it sounds like word salad to me
The problem with the channel at the moment is that it builds on top of previous episodes, I got into it when it was still understandable to me; check out the older videos and go from there.
Judging by the comments, that seems to be a common sentiment among viewers :)
I came here to reccomend this channel aswell. The "basics" were all covered years ago (6+), and now Matt is dipping into more complicated topics. If you find his recent videos overwhelming, I suggest to give his older ones a try.
Sean Carroll (professor of physics, quoted in the article) has a highly-rated book titled "Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime" [1] which discusses exactly these topics. I haven't read it, but it's on my list.
I also highly recommend his podcast "Mindscape" where he discusses this and a range of other topics in science and philosophy. [2]
[1] https://www.preposterousuniverse.com/somethingdeeplyhidden/ [2] https://www.preposterousuniverse.com/podcast/
Great question and I’m hoping to see some other recommendations here.
In my opinion Coveney & Highfield’s 1990 survey “The Arrow of Time: A voyage through science to solve time's greatest mystery” is better than most for clearly connecting where theoretical approaches like many-worlds to the context they arise at the intersection of relativity, statistical thermodynamics, and quantum theory https://en.m.wikipedia.org/wiki/Special:BookSources/978-1-85...
As the book is 30+ years old and predates what I have to assume to be significant progress in the respective fields I would be keen to know if the experts here are aware of updated sources at any level (peer reviewed papers, monographs, etc.)
There are great video series on YouTube, for example:
https://m.youtube.com/@pbsspacetime
https://m.youtube.com/@HistoryoftheUniverse
I often find videos easier to follow due to the great visuals.
You can also listen to interviews with the authors on podcasts. They talk about their books and the concepts in them.
And as always, your favorite LLM is a great companion to help you understand. I've consulted it several times and the answers and links it provided were very helpful
It’s very much a Copernican boundary: human beings desperately want to be at the center of things.
At one time this meant being at the center of the universe, today it’s more like wanting to be at the center of a unique identity with a deterministic past but an undetermined future.
This has led to countless interpretations of e.g. the Born Rule where humans have a unique ability to force wavefunction collapse with their senses.
Hugh Everett and those who subscribe to his post-Copernican view assert that we’re better off discarding the parochial attachment to a unique identify of experience than we are discarding theory validated by experiment beyond credible doubt.
One cannot truly avoid being human-centric, if the territory of reality is never available to one other than a map constructed by one’s consciousness. The core conceptual constructs used to reason about reality, the ways of attending to reality, the approaches to measuring it, this is all inherently coloured by humanness and further distinct cultural predispositions (a Western natural scientist is biased in one way, a !Kung shaman is biased in another). To assume the possibility of an unbiased take is unreasonable.
(There is never a complete map of the territory that covers the entirety of the territory in a way equally suitable for every possible use. Such a map would be the territory itself, which is not made directly available. So it’s good to have different maps, and to acknowledge that none of them can be assumed to be correct/complete.)
That said, assuming the hypothetical ability to cause what we refer to as “wavefunction collapse” via observation does not seem to strictly imply a human-centric view. Humans may be treated as a particular kind of conscious observer, but in a monistic idealist take assuming they are alone in that seems insufficient to describe reality.
Your argument isn’t with me, it’s with iconic physicists spanning the range from Sean Carrol to David Deutsch.
I’m well aware that any argument against vibes around an asymmetrically deterministic universe with a clear arrow of time and a unique dualist window of self is going to be unpopular.
There isn’t any physics there: how one chooses to interpret and integrate the vanishing impossibility of free will or unique identity is a very personal matter.
> Your argument isn’t with me, it’s with iconic physicists spanning the range from Sean Carrol to David Deutsch.
Of course, and (maybe more importantly) a number of philosophers. However, other philosophers (and, indeed, some iconic physicists) might not disagree.
> any argument against vibes around an asymmetrically deterministic universe with a clear arrow of time and a unique dualist window of self is going to be unpopular
Dualism is popular in general population, but monistic materialism is probably more popular among the tech crowd. Both approaches don’t strike me as elegant, naturally.
> how one chooses to interpret and integrate the vanishing impossibility of free will
Well, how one chooses to integrate the consciousness being the only thing that we can assume objectively exists (as the only thing we have direct access to, empirically) is also personal matter. The ways of waving it off (pretending it’s an illusion, etc.) are many… Once you stop doing that, though, suddenly free will is no longer such a crazy notion.
Humans also desperately want to find something that transcends them. But so far failed to find matching QM interpretation with new explanatory power.
Physics and mathematics have yet to answer age-old questions about the meaning of life, and it’s understandable that this would be disappointing! Our most intelligent people, adequately if not always amply funded to probe the deepest mysteries of the universe have come back with: “there is no evidence that it means anything, or really that it even happened in the way you mean”. Who wouldn’t be disappointed?
But this is ultimately a failure of our priests and politicians and parents: it’s not the job of scientists to be our nursemaids in an indifferent cosmos. We have people for that role, at least on paper.
"We have people for that role" is exactly the copernical boundary, that he transgressed :)
Just for context as a fellow interested noob: That book in particular is more like a manifesto than a survey, so it's not really intended to be 100% convincing, IMO. And AFAICT most of that book is about using the philosophy of the multiverse, not about justifying the physics -- so you definitely shouldn't feel bad coming away with that conclusion. An infinite multiverse is, to say the least, controversial!
For recommendations, assuming the linked articles themselves aren't up for grabs, I really liked The Rigor of Angels for a more historical-philosophical view on quantum physics, and how it compares to its predecessors. I also constantly reccommend this other Quanta article from a few years back, which is shorter and more cohesive than these: https://www.quantamagazine.org/what-is-a-particle-20201112/
Sadly, I think this whole field has an inherent level where it breaks down for non-experts, epistemologically speaking (how appropriate!). Watching Hossenfelder's engaging YouTube videos has taught me one thing above all else: I have no hope of critically engaging with the fine details of modern theories, only the metaphors and stories that surround the math.
What about if these people, despite their special terminology and maths, don't know either, and they're all just acting like they do? Stranger things have happened.
I recommend Carlo Rovelli's books.
I think we're already at a point with LLMs (namely ChatGPT and Claude) where everyone has their own personalized Physics professor that you can ask any question you want. You can even say "explain it to me like I'm 5" and it will. You probably already knew this tho. :)
And the explanation may or may not be total nonsense.
Good luck figuring that out on subjects you don't understand.
Take the content, paste it into chatgpt and ask it to explain it with simpler language, more details and examples.
My understanding of black holes is rather straightforward, gravity is so strong it prevents light and matter from escaping it's orbit. That does not mean that nothing is there or that all physics as we know it breaks down. Simply that our instruments can't observe what's there directly.
If you deepen your understanding it suddenly stops being rather straightforward.
Here's a good playlist to warp your head around the subject.
https://youtube.com/playlist?list=PLsPUh22kYmNBl4h0i4mI5zDfl...
Not so simple. If there is no collapse into a singularity, what happens to the matter? Theoretically speaking, we have no clue to what happen to matter beyond neutron stars levels of degenerate pressure.
Specifically, what happens to fermions once all the quantum states are filled and they are still constrained by all the other fermions around them? We have no idea (and everything seems to point to a collapse into a singularity).
If, instead, there is an actual singularity (which has infinite density) it means that the curvature of space time is infinite, which our current theories can't cope with. Additionally, if singularities have infinite density, how is it that black holes can have different masses? A singularity can only be characterized by its position in spacetime since it has no size and so there is no space/surface for it to have any other property and yet we see that there are black holes with different masses. Another thing we can't explain with our theories.
So yeah, black holes mess with our theories in a fundamental way because as soon as you start pondering what happens inside them we discover that general relativity or quantum mechanics or both break down and so they must be incomplete. Spacetime, being a construct of general relativity is therefore also an incomplete description of the real fabric of space time.
Ok, but in my mind it's a lot like a mystery box, there's a lot of speculation about what's in the box, but without new instruments or new observation techniques, if the light/information from inside isn't reaching us we'll probably not be able to prove what's going on in the box one way or the other. One can claim "space-time breaks inside the mystery box" all you want, but I haven't heard of any testable theories.
Perhaps, but in terms of getting things done and making progress, it isn't very useful to suppose that it is simply a mystery box and that's that.
Because if we just accept that, what do we do then? We just sit and wait for some new astronomical observation to give us a clue? that could take forever, and we'd be banking that we have the tech to observe this magic hint.
Better to suppose that the theories we have comprise an accurate approximation or partial model of reality, and from there strive to find a better model.
The process of doing so will either refine/entrench our current model and our conviction, or it will result in actually finding a better model. Win-win, and all the while, we can still have our telescopes and detectors on for the magic hint we'd be sat waiting for anyway.
When things break down into singularities, it can be a pretty good indicator that we've got something wrong. Not necessarily, but in this case, I think we missed something.
Quantamagazine is pretty amazing. The content, the visualizations, no ads, it’s loading pretty quick - I think this is how the web should be
[stub for offtopicness]
I come here for the plaintext.
Scrolling through that site is like geek kryptonite. Terrible. I will monitor this comment thread for other articles which cover the same content.
Wow, hot takes. All of this is because the intro quotes appear and dissapear? Otherwise it doesn't actually hijack your scrolls other than to slide in some incidental images, and this is just the index, anyway -- all the articles are plain print articles with no animations at all.
I had just whitespace on mobile for pages and pages before text started appearing.
This site deserves my wrath, and the wrath of others. You have a browser which works with it obviously.
A) I like cute scroll effects, but maybe we should consider making them additive rather than completely ephemeral (when screen size permits)? The intro is beautiful on mobile, I'm sure, but it's just kind of irritating on desktop.
B) Thanks so much for posting, I had skimmed a few of these articles but didn't realize it was part of a cohesive series. For others, since it's not really obvious at first: the whole series is built to setup the three articles at the bottom, where Charlie Wood examines three competing research groups. Quanta is on fire these days... This is an amazing evolution upon 2020's What is a Particle?, which is an article I've been bringing up in like every other conversation b/c it's so fascinating and accessible.
C) Other than the initial complaints about the intro, the article itself is downright groundbreaking webdev-wise. And I called it when I started this comment -- the rest is additive!
The way the text deforms around the sliding divs (but quick enough that it probably won't interrupt you since you haven't gotten to it yet) is just beautiful, I don't think I've seen that before. The dynamic, freeform cutouts fit perfectly with the theme, and the background is bold (how many sites are purple??) but indescribably perfect. Of course, the star of the show is the animated "thought experiment" page, even if the transitions are atomic (can't be reversed halfway through by scrolling back up). And the final summary + animation is worth scrolling to the bottom for, even if you don't read the rest of it.
Well done Quanta web team, you're seriously raising the bar with this article, IMHO. Inspiring stuff. Is there any magazine ~~article~~ "series" (issue?) that even approaches the beauty and cohesiveness of this one? I'd love to proven wrong by the experts on here ;)
[ETA: wow everyone hates the UX, I'm shocked. Why, in particular...? At the end of the day the linked page is just a list of links that appears right near the top, I don't understand the ubiquitous hate! What am I missing?]
D) I'm pretty far from critically evaluating the physics surveys themselves, but I certainly found them helpful. Some quotes that are just insanely insightful, the kind of simple, boring statements that edge on superstition through their pure profundity alone:
In periods when we are looking for new theories, physics has always become philosophical.
Our natural perspective as beings with locations separated by space sticks out as a mathematical oddity. “It’s a reminder that the laws of physics that we perceive in our world don’t seem to be random,” said Sean Carroll (opens a new tab), a physicist at Johns Hopkins University. “They seem to be specific.”
“AdS/CFT is an insane suggestion that should be stupid,” said Geoff Penington, a physicist at the University of California, Berkeley who studies holography. “But then you try all these things, and it all ends up being consistent.”
For his part, he feels that holography isn’t radical enough. It shows how one dimension of space could emerge, but otherwise all the familiar ingredients of quantum theory are there from the start: some space, locality, and a clock to mark time. Arkani-Hamed feels that all of those elements should emerge together from something more primitive — as they do in surfaceology.
It might seem like I’m interested in lots of different things, but I’m not sure if they’re really all that disconnected. At least within math, it is kind of true that sufficiently beautiful things tend to be connected with one another.
So the key to black holes’ underlying structure exists on their surface. “People began to think,” Law said, “that maybe whatever microscopic theory describes black holes lives in a space-time with one lower dimension.”
Sorry for the spam, won't mind if this is deleted -- it's just terribly helpful to write as I go. If you're scrolling by, I highly recommend bookmarking this series in full! And if you work at Quanta and are reading this: you're awesome.
> F) Even more fundamentally, can someone explain why we can't just assume that there isn't spacetime inside black holes? If everything's pointing towards their contents being entirely contained within their infinitely-thin surface, why can't we just embrace that?
It's not that simple. The surface at the event horizon is not a physical thing, it's a coordinate singularity which is only apparent for a very distant observer. If you imagine two spaceships flying towards the center of a black hole within close distance, they would notice nothing unusual when crossing the event horizon. They would be in constant radio contact. It's mind bending stuff, really.
> F) Even more fundamentally, can someone explain why we can't just assume that there isn't spacetime inside black holes? If everything's pointing towards their contents being entirely contained within their infinitely-thin surface, why can't we just embrace that?
You're not crazy, that's my pet theory too!
Spacetime in physics has always been an imaginary mathematical construct. Spacetime is not something that exists in reality. Take the deflection of light equation used to compute the deflection of light in General Relativity:
alpha = (4GM)/c^2*r
This equation contains no terms for something called “spacetime”. This equation does not say that the light is bent by spacetime or that this observation is done in spacetime. But physicists write a fictional story over this equation and pretend that spacetime bends the light. The equation doesn’t say that, physicists do. And now physicists decided that spacetime does not really exist, it is emergent etc. Just a few years back people who said these things in forums would be dubbed crackpots by physicists.
It's a bit more involved than that.
That simple equation you quoted has been derived from the geodesic equations. Geodesics are the equivalent of straight lines on curved manifolds, which is a mathematical object. The shape and geometry of the manifold in question, which in turn influences the shape of the geodesics, is given by the matter distribution, or more specifically the energy stress tensor. The relationship between the manifold and the energy stress tensor is described by the Einstein field equations.
We gave that manifold the name "spacetime".
This couldn't be further from the truth. Even just in special relativity, if you want to compute the age of an object on a very fast ship, you need to use the Lorrentz transforms, which categorically use a metric for the space-time. It's at the base of everything else in relativity.