IANAP, but as a mathematician it seems extremely inelegant that there would be a start to the time dimension of the space-time object we live in, when we don't even know if the spatial dimensions are finite themselves.
It is my understanding that the density of the universe billions of years ago was radically different from the one we now observe, and since density is intrinsically tied to our perception of space and time, wouldn't it make more sense that time actually stretches infinitely the further back we go, thus nullifying the concept of a beginning?
I guess I'm having a hard time with the idea that space-time could be discontinuous.
The question is "how long has it been since the big bang." It's an important and relevant question for cosmology and physics. It isn't really a stance on the "beginning of time," which may have started long before this moment, but it is the start of the universe as far as physics is concerned.
How I work it out in my head that time effectively did not exist before the big bang is that; If everyone agrees that time slows as the gravity increases, and we assume at the time of the big bang that all the mass of the universe was in an infinitely small space, the conclusion is we had an infinitely large gravity and time would be effectively be stopped. Take it with a grain of salt.
Exactly. It could even be turtles all the way down, with new building blocks of physics becoming relevant as we go smaller and smaller (and back in time).
I like this. But you still have a Prime Mover problem. If time effectively halts at T0, then what possible event could occur (outside of time?) to nudge that infinitely large glob off mass into the motion we observe today?
T0 includes the prime movement in its definition. If the universe never emerges, change never exists, so it’s not anything (including not T0). Conversely if we know it was T0, it’s because we know things started happening after that.
The universe advanced from T0 because it had to, by definition.
If this seems like a weird cop-out, well, that’s a singularity for you.
The glob of mass starts off in motion at T0, there is no time prior to T0 in which a glob of mass exists waiting to be nudged.
Think of it like a particle decaying - at some point it just happens with no trigger or internal mechanism, and now you suddenly have the decay products wizzing about with some energy and momentum that they just start with.
This is where we see the limits of science. It's a great tool and a lot of benefit came from it. But at some point we encounter things beyond its domain. Us people of faith know that God is the cause of existence. In Islamic Kalam we have a phrase (Wajeb Al-Wujood) - meaning The One who's existence is obligatory/fundamental - i.e. God.
> If time effectively halts at T0, then what possible event could occur (outside of time?) to nudge that infinitely large glob off mass into the motion we observe
today?
Anthropic principle explains it. If you need a Prime Mover, you can also replace it with Anthropic principle and random chance.
For example if time halts at T0, physics breaks. Using limes when t->0 you get that v-> Infinity (or c). Slower time moves for you, faster you move in space. At that point, if nothing is there to detect it, every massless particle will be effectively everywhere, all at once. Essentially photons can have Infinite energy and just cause a random Big Bang. This is CCC like explanation.
Another answer is Hawking's North of North Pole time problem (from Universe in a Nutshell). If time halts a T0, you can't ask what's before it. It's just logical impossibility. Like what is North of North Pole? Answer is: Question is invalid. Anthropic principle implies there are however many multiple such configuration so you get a parallel or sequential universe solution.
We arise and wonder how exactly Universe exists that support life, even if we can clearly see, it's only supporting life at this moment. Our existence is a grain in the sand of a universe-sized sand clock that will be the Black Hole epoch.
No, I am not. I've demonstrated my work, you can prove me wrong using an argument rather than "you're wrong". Universe doesn't have to have a why. And science isn't dealing with such metaphysical questions. That's realm of philosophy.
The principle of sufficient reason states that everything must have a reason or a cause. This is not a principle to lazily toss aside to avoid some more difficult question, it is a foundational idea.
Our understanding of the world (aka science) is largely based on causality, and if things existed without any cause or reason, our understanding of "science" would probably be very different.
(I'm not a physicist, but this is how I understand things.)
I mean... that's a pretty superficial reading of the situation. Where do you stop? If you assume Newtonian time, which extends back to minus infinity... well, what caused time to exist at all?
Also, no one is "lazily tossing it aside". It comes out of the mathematics that describe the observations:
Say you find that all observations you make are perfectly described by dx/dt = 1/x with current time t1. If you follow the trajectories backwards, you find that the trajectory can not be extended back past some initial time t0 at which x(t0) = 0 as the equation becomes singular then. You are now at time t1-t0 from the initial singularity. That is the age of the universe since the big bang. Now the trajectory as it approaches t0 has some unusual properties, it moves infinitely fast, etc... These might lead you to postulate that unknown physics will actually invalidate your law as you approach t0. But there is nothing logically or epistemically _wrong_ with the law you have. The finiteness of time flows out of a causal empirical induction argument. It is not introduced ad hoc to avoid some difficulty, it just is how we find nature to be at the most conservative interpretation of the evidence.
In that case, we are not disposing of any principles (as you originally claimed) when we have an uncaused first cause at t = -13.6 Billion years, instead of having at t = - infinity.
I'm not sure "accepted" is the correct word. It is a feature of our current theory, but we know that theory is incomplete. In particular high density regions such as the very early Universe are where we know ate theories start to break down, as the conflicts between quantum physics and gravity become relevent.
There are proposals for time stretching infinitely back, but we have almost no way of testing them.
If time is stopped then why did it bang. The fundamental character of time is ability to change. If time is stopped then there should be no change. Otherwise time wasn't stopped.
Maybe I guess. Many models stipulate that time began with the Big Bang. Many propose the Big Bang was a local event that obliterated our ability to observe time before it. We have models where the universe rips apart, collapses, or just evolves forever and always has and always will. I think what’s crucial to understand is we have a lot of different possible explanations for what we see, some of them discuss beginnings and ends, some do not. Perhaps as a mathematician with a relatively closed set of possibilities for explanations that’s unsettling. But, I’ve always found the various paradoxes in math to illustrate similar problems in formulating a closed and coherent anything, including the universe.
One thing I have always wondered, since gravity is proportional to the mass of the two objects and inversely proportional to the square of the distance between them, if the universe was smaller with the same mass, wouldn’t gravity have been more “dense” in an earlier universe?
And since we know that gravity affects the rate of flow of time, wouldn’t the rate of time be enormously distorted earlier universe?
I’m not trained in any of this, so hopefully there are greater minds here who can help me understand
> inversely proportional to the square of the distance between them
As I understand it, that’s an approximation for Euclidean space because the area of a sphere is also proportional to the square of the radius in such a space, but it’s not true of non-Euclidean spaces like in GR because the area-radius relation is different.
IIRC, the cosmic microwave background has a gamma factor of about 1100, so the area of that shell is the same as one 1100 times closer or 1/1100^2 times the area as a Euclidean sphere with that radius.
> And since we know that gravity affects the rate of flow of time, wouldn’t the rate of time be enormously distorted earlier universe?
Time did indeed slow down then compared to now, although it’s not entirely obvious to me that this has any physical interpretation when it happens “everywhere”: https://youtu.be/66V4RSmDqYM
My understanding is that time was not slower (whatever that would mean), only that the expansion of the universe means that light is stretched. So events in the early universe appear to happen 5 times slower.
We know that the force carrying particles of all forces have a frequency, just like any other particle. That means that if particles on average move faster than, say, double that frequency, they can't exist.
So there must have been a time when electromagnetism, the weak and even the strong force just didn't exist. They couldn't. So particles would just have totally ignored those forces.
We don't know if gravity is the same, but ... why wouldn't it. Though of course according to relativity gravity just wouldn't care, but that just raises a lot more questions than it answers.
I don't think there's a good answer to this question, at least not when it comes to the nature of particles and light, because we don't have a good answer to what movement and time are. We already know both light and particles are you moving relative to fields. Light is you moving relative to an electromagnetic field. If you move towards a magnetic field you would find it starts "glowing", in fact, that is what light is. But it's not like a magnetic field reacts to you because you start moving.
The issue is that movement and time are fundamental to the universe, yes, in the way relativity describes but also in a totally different unknown way. In some ways particles are "just" things moving relative to one another. Which, for one thing, brings the perspective question (if you accelerated to a "real" speed, would you see a different universe? Because you would disagree with us slowpokes here on earth on what particles exist at least in some cases. But would you see an entirely different universe?)
> It isn't really a stance on the "beginning of time," which may have started long before
Well... yes it is, in the rigorous sense of "time" defined by general relativity. There's no "before" for a singularity. It may not be the whole story, but whatever metaphysical notion defines the "before/beyond/outside/why" that drives the big bang, it's not a place on the "time" axis of spacetime.
Specifically, GR is a model that breaks down at singularities. That time "begins" at the Big Bang is a prediction of GR, but until we have a model of quantum gravity there's no telling whether that's actually true or whether the conditions at the big bang are something GR can't fully describe.
Similar to the singularities in black holes - everything up to a stone's throw of the event horizon is pretty well explained by GR, but as far as the horizon itself or the region beyond are concerned, there might be dragons as far as we know.
> That time "begins" at the Big Bang is a prediction of GR
I don’t think that’s right. If we interpret Big Bang theory as claiming that there is a singularity at a finite distance into the past history of every present event, then GR can’t predict what happened at or prior to that singularity. Whether time “began” then or whether there was “more time on the other side” is a question GR alone cannot answer, not a prediction of GR
Black hole singularities do not start right after their event horizon. The event horizon only demarcates where the black hole singularity becomes an inevitable (inescapable) point in all possible futures.
That's not what I was trying to imply, sorry. It's the singularity at the center where GR entirely breaks down, but there's also weird stuff going on below the event horizon (space becoming time-like and vice versa), that aren't present in, e.g. String Theory's Fuzzballs [1] (which, of course, bring their own set of thorough weirdness). So what I was trying to say was that while GR predicts some behavior below the event horizon, a full model of quantum gravity could predict something entirely different, and not only for the area just around the singularity itself but (maybe) up to the event horizon.
How does that work for black holes? It seems like there would be a 'before' they formed in the time dimension of our universe, if not within the singularity itself.
For blackholes it's the reverse, all paths lead to the singularity, and there is no 'after' as opposed to the big bang where all paths lead away from the singularity and there is no 'before.' If you hit rewind on a video of matter falling into a black hole's singularity, it would look like a big bang where everything was created from nothing at an infinitely dense point and starts flying outwards.
Think of singularities as unidirectional. We don't understand what if anything was before the big bang, there is no return from inside a black hole event horizon, we don't understand what would follow after an AI singularity. That doesn't mean that they don't have a threshold in time/space/spacetime, just that crossing that threshold breaks the rules we know.
Singularities are mathematical constructs and are used to model different kinds of phenomena. Black holes and the big bang are only roughly comparable (but by no means similar) if you are considering a black hole from "inside" of one.
There might literally not be enough time to expand beyond that, given how cosmological horizons work. Being part of the system we're trying to observe puts some nasty limits on what we can know, even in principle.
I agree we practically may never know and fundamentally the rules of the universe might end up making it impossible to know somethings, but as far as I know the ultimate limits are currently unknown so 'We can hope ...'.
There’s an alternative take that says that, as the universe contracts, it eventually hits a point where other effects (quantum, but also possibly unknown effects) predominate and that this kicks off another stage of expansion.
Which is to say that there exist respected papers that outline this scenario in great detail, but there’s precious little observable evidence of a previous universal cycle.
It's unclear what exactly you have in mind, but the equations of GR simply predict that the topology of space-time is not that of R^4, but includes boundaries at finite (temporal) distance, so-called space-like singularities [1]. This is not unusual. For example, the solutions to the ODE dx/dt = -1/x topologically live on the half line.
As a fellow mathematician, I think maybe the right way to think about physics is that the claims are never even supposed to be “true” in some absolute mathematical sense. It’s more like true to some first approximation.
So maybe we can interpret this claim as saying that 25 billion years ago, the universe was kinda similar to what we have now, but 27 billion years ago everything was ultra compressed and gravity didn’t have a significant effect on anything. Or maybe time is like a left-open interval. Finite, but didn’t have a start. I dunno, I’m making stuff up.
Left open interval is the right way to view it. There is no contradiction or paradox here. Merely unfamiliarity. But maybe you should not expect the rules of the early universe to be very familiar...
Physics is only true modulo theory. It’s intense intellectual arrogance to say “because this model predicts some phenomena the world must conform to this model.” Newton, who I think it’s fair to say was not known for his humility, refused to feign hypotheses and satisfied himself with describing his observations.
However in today’s day and age that way lie no fat grants, adulating television specials, or NYT bestsellers.
It is my understanding that the density of the universe billions of years ago was radically different from the one we now observe
It’s even more puzzling than that. Our current model features a period of time called the inflationary epoch which lasted between 10^-36 and 10^-33 or so seconds after the Big Bang, in which the universe expanded by a factor of at least 10^26 along each linear direction [1].
This is unfathomably rapid expansion. It makes sense mathematically but not at all intuitively. It’s totally bizarre and weird and I don’t have even close to the level of background needed to challenge it!
> There's a 'most northern' point on the earth, and the surface is arguably continuous.
This was Hawking's point of view. One way of thinking about special relativity is that time is at right-angles to space, and everything travels at the same 'proper' speed (c) through this 4d spacetime, just in different directions (hence why "fast" objects experience "time dilation": their 4d heading is pointed largely in a space direction, so they don't progress much in the time direction). This extends to general relativity, which describes how these directions "bend" into each other. For example, the reason objects fall due to gravity can be described as spacetime curving such that "future" points slightly "downwards" (and hence slightly less in the usual time direction; which, again, causes time dilation).
AFAIK Hawking's idea was that the curvature at the big bang was so high, that "past" is pointing completely in a spatial direction; and hence there's no such thing as "earlier" anymore. Similar to how "north" near the north pole is at right-angles to "north" at the equator.
This isn't really what "start" is usually intended to mean. They're just identifying the time of the Big Bang, beyond which any possible causal connection is lost and we can't possibly look back further. More time, more space, more something else may have existed and been causally prior, but we can't meaningfully talk about it except speculatively. It isn't part of our spacetime.
Of course, people do speculate. I seem to recall some level of anisotropy in the cosmic microwave background that was a bit more than expected purely from quantum vacuum fluctuations in the pre-inflationary early universe and at least one physicist musing that it might be a perturbation from some other universe that has since lost causal connection. This, of course, makes no testable predictions, can't be falsified, isn't really science, but human intellectual curiosity goes beyond science.
I think that by definition if the universe was at one point a singularity then there is a start to time and space.
This idea goes all the way back to Plato and his Parmenidean-inspired rejection of the Pythagorean notion of the Monad as being at the centre of the universe as the Number One implies certain properties like perfection, unity, etc., and we see none of those properties in our existence. This led Plato to argue that the One existed separately from our reality, which was just an imperfect copy associated with the idea of an indefinite Dyad.
So it wasn't just that the universe was a densely packed packed ball of all the stuff we see today and it somehow spilled out or burst forward, what existed before was a monad, and all the stuff we see including space-time, the elements, and more were created at the time of the Big Bang.
> wouldn't it make more sense that time actually stretches infinitely the further back we go, thus nullifying the concept of a beginning?
I believe it could be 'turtles all the way down' as the phrase goes. Maybe our Universe started by a collision of two or more other Universes and we got this mess called the Big Bang. This doesn't explain how those other Universes started though.
But then as mere humans, we can't conceptually grasp Infinity itself. This is not some failing of ours, it's actually convenient to not imagine infinity, as it would drive us mad. The minute you include the Infinity Symbol (∞) in a math equation, all logic starts to cease and get very wobbly.
> Maybe our Universe started by a collision of two or more other Universes and we got this mess called the Big Bang.
Once upon a time I watched PBS Nova program about string theory. I remember they talked about something along these lines. It's been almost two decades since I saw it so memory is rusty. But it was something along the lines of universes existing in these big "planes" (they visualized them like these big floating membranes) that would vibrate and occasionally smack into each other. When one of these collisions would occur, there was the potential for a new plane to be formed from that collision.
Like you said, that could potentially explain where new universes come from, but not how the other "turtles" got there in the first place.
There’s a theory that the birth of our universe looks eerily similar to what might happen inside a black hole when it’s first formed. Fun to think about.
I propose the universe exists in itself. That the interstellar space - is the same as subatomic space. Its both at the same time, like a möbius strip. Space between stars is space between atoms, etc.
This is my favorite hypothesis, even though/especially because it makes your mind spin. I could be wrong but I think Roger Penrose has some thoughts along these lines. I may be butchering this and/or injecting my own (admittedly ignorant) pontification into it, but:
The universe will keep expanding until entropy reaches a maximum -- the "Big Freeze." Once maximum entropy is reached -- wherein all atoms in the universe are totally dispersed, everything is the same distance from everything else, and the universe is a totally uniform field -- one could say that is very orderly indeed, i.e. the theoretical minimum entropy.
I imagine that all of the matter in the universe being perfectly dispersed would quite neatly "fill" the universe. So who's to say such a situation isn't infinitely dense?
Other than theoretically, the spatial dimensions can only ever be observed to be c * T where T is the total age of the universe. Thus, space is bounded as well. It all comes down to what it means to be bounded.
If something preceded the big bang, it cannot be observed (by our current reckoning). Similar to things farther than cT away... Unobservable; unknowable.
There's nothing inelegant about it. C is the conversion factor between space and time.
My understanding is that in models where time began at the Big Bang space typically also began concurrently. Before this time (harhar) there was nothing, but that’s meaningless because time also didn’t exist. It’s immeasurable before a certain point. Likewise space began at that time and expanded to fill all space rapidly, which I’m often a little unclear here, but my understanding is in a similar way to how space expands today outside of galaxies by space simply expanding from within itself (I.e., without force or movement). This conceptualization might help quiet that discontinuity discomfort.
I’ll search for it but PBS Space time has some wonderful intuition building visualizations and explanations in some of their parts on models for the beginning of the universe. If I can find the ones I’m thinking of I’ll edit later, but regardless I find their background material on “wtf” re: physics can be helpful.
AFAIK (pardon my limited knowledge of physical and math terms) the spacetime interval is the conserved unit and it has a lower bound in the Plank-scale limit.
In the paragraph above, you assume time is a primitive concept, but it is really an emergent phenomenon. The passing of time, moving by some amount of (the plank-scale limit of) spacetime interval, can happen only across connected configurations.
Think about evolution in spacetime as a combinatorial game, there can be positions where causal links are not possible, or even empty games.
FWIW I don’t think it’s certain yet that time cannot be divided smaller than the plank limit. I remember reading an article some years ago about an experiment indicating that there seems to be no smallest “slice” of time. Unfortunately I can’t find it and my patience for searching google these days is pretty low.
As a mathematician, I don't think about Big Bang as the "start of time" (or any other dimension), but simply as "fixed point" (of the "physical evolution of all particles in the universe" function).
It's not a fixed point of the equations, though. That is technically incorrect and also not the right intuition. It's the exact opposite. It's a point at which the acceleration of (the density of) all particles diverges, and thus the equations can not be continued past that point.
There’s a start to the space dimension as well. Imagine a ball 10cm in diameter, it’s possible to imagine a ball that is 9cm smaller than it but not a ball 11cm smaller.
While I agree with you on this "hack", I also believe that if we accept that geodesic incompleteness idea is right then time for all intense and purposes has a start. At least as observers within the bubble of space-time that is causally connected.
If time/space-time existed before the BigBang is probably an unanswerable question (unless we are within a 4d black hole and we can listen to waves that perturbed the matter before the formation of our universe).
> If time/space-time existed before the BigBang is probably an unanswerable question
Why? Any sign of another Big Bang going from some other point somewhere else would indicate that "our" Big Bang might not have been the first one. It is harder to prove absence though.
Because if inflation is also correct we lost every causal connection with whatever was there before, or is so diluted that we might not be able to detect.
Another possibility could be that at the time of the BigBang the energy density was so high that everything was unified, and so when forces actually separated they "tabula rasa" anything that occupied the bubble of space-time we expanded into.
However, it could also be that the fluctuations we see in the CMB are due to perturbations of what happened before. But that possible clue is better explained by comic inflation expanding quantum fluctuations at an incredible speed that disconnected them.
That's why I said it's (probably) unanswerable. I also hope I am wrong though.
It could be that our ideas about infinite and continuous values, so-called real numbers, are nothing more than a good model/abstraction up to some point.
One way to consider it would be taking the limit of 'space' as time approaches negative infinity from a zero point of today. That's kind of silly considering they are coupled, but for practical purposes it is the effective point of 'the big bang'.
Why not? Tons of things are, for example, entropy. I have a crackpot idea that the Big Bang itself was just an "entropy population inversion." The big bang is literally just the moment where the discontinuity occurs.
Another idea: at the end of times, when black holes finish merging into one giant black hole, will it force a big bang like event? If we assume the universe to be a large 3d sphere, what's the topology of space in it if it's just one giant black hole?
Why would all black holes eventually merge? The mass in our observable universe is constantly decreasing, with more and more of it going forever beyond our reach. For any two distant black holes it seems more likely that they will eventually find themselves forever alone in 'their' universe than that they will merge.
Similarly, I find the idea of the end of time to be weirdly unreal and impossible. It feels like time is not a thing that has a beginning or an end, and that it would just stretch and dissipate infinitely into the future.
You can still imagine that as an end, and define an end based on that infinite stretch. At some point, you can't tell the difference between before and after more stretching, and you'll never be able to stretch in a way that can be noticed.
There's no more events to happen, and more so, no ability for more events to happen.
Thats still likely an artifact of our models though, and that when you do to something like that, that new events start happening again
I'm not sure if Penrose suggests that time stops once there are only photons left. He says it is equivalent to the situation at the Big Bang and time certainly didn't stop there. In fact, in his conformal cyclical cosmology spacetime goes on indefinitely but just reboots regularily.
As I understand it, 'the beginning' is when 'the universe' had a 'once-in-a-gazillion' moment where the probabilistically unlikely event of entropy shrinking to a very small value happened ( aka 'the beginning' ) and from whence entropy started to increase again as it is wont to do.
It all goes back to thermodynamics and the probabilistic understanding that entropy 'always' increases. But if entropy always increases then by reason, it must have started off at small minuscule point sometime in the past. But if energy/mass are constant, how could it have gotten to the low entropy in the first place? Given enough time, a 'once-in-a-gazillion' event actually happened. At a fundamental level, it's all mathematical guesswork.
The tone of the headline makes it sound like 26.7B is now accepted, but the article indicates it’s mostly just a theory that has a little additional evidence. Is the later a correct reading of the situation?
It's all just theories. But yes the article is basically summarizing a new paper/model. Most likely: the model is incorrect in some ways. But maybe useful in others.
Do you mean hypothesis? A theory is a well-substantiated explanation based on evidence...and has undergone some kind of rigorous testing/verification. A hypothesis, on the other hand, is "just" a proposed explanation/prediction based on little (or no?) evidence...which is then tested through experiments, etc.
A hypothesis is a proposition. A theory is a model. The two are different concepts but neither implies rigor or lack of rigor. It’s harder to build a complete model from nothing but it happens all the time.
Theories about the universe as a whole (or anything outside the solar system at this point) can't really be tested in the normal sense. You can make a theory and then try to look for more data/make observations about the universe and see if they match, but there's no control and you might never get the data you need to say one theory is better than another. You can get lucky of course, but it's not like you can recruit 40_000 universes for a double blinded placebo controlled clinical trial.
You can at least test some parts of quantum physics and general relativity on and around Earth, with satellites in orbit with very precise clocks and double slit experiments and that sort of thing. For everything outside the solar system you can just observe and hope new data arrives that you are not already unblinded to.
Try to convince a member of science's fan base (which includes many actual scientists) of this during an object level discussion about a particular point of contention and see how well it goes over.
Yes, you are correct that it is not the widely accepted number as of now, and that it is just one theory. It's just that without this tone the headline would have never made it to the front page.
Our upvote tendencies incentivize drastic tones, so it's effectively what we ask for, and what we get as a result.
Had to check Wikipedia[1] just to be sure this was actually an accepted number.
That still says ~13B years right now. The headline is edited to be more sensational than the actual linked article.
Perhaps the title would be more accurate if it were "The way my friends and I prefer to think of it, the age of the universe is nearly twice as old as we used to like to think of it."
Pop science in general doesn't pay enough attention to which theories are solid and believed to be 99,99% true, and which are just accepted as best guess in lieu of good data. Although history (not science, pop version) is a much worse offender than physics in that regard.
Theories without data are just Philosophy in mathematics based drag.
It doesn't make it pointless but one has to treat it for what it is. It was like String theory, it was all well and good but without a meaningful experiment to test it - it could only go so far.
Sure it does. A theory that has little explanatory power due to the lack of available evidence can, in the diminutive sense of "just", be called "just a theory" where the understood context is comparative to a theory with a high level of explanatory power and perhaps a general consensus among experts in the field.
Even something that's just a theory is not to be confused with "mere" conjecture, and somewhere way down in the hierarchy have "pure poppycock". Though even pure poppycock on occasion rises up through the ranks, much to the embarrassment (often post-mortem) of those who pooh-poohed it previously. Of course "pooh-poohed" is not a generally accepted scientific term, I use it here as a mere colloquialism. I'm sure (though not certain) that people already understand that and wouldn't bother being pedantic about it.
I remember in middle school I had a very passionate physics teacher who held extra astronomy classes for kids who wanted to join.
Particularly I remember when he presented the age of the universe.
The age was estimated with something like plus minus 10 billion years. The teacher made a big deal about how incredible this was. When I first heard that number it sounded beyond imprecise. But he explained: Now we actual had a ballpark figure. Before we didn’t know if it was thousands or quintillions of years, so plus minus 10 billions was really good and ground breaking.
With that in mind, this kinda seems like a minor adjustment.
I was in middle school in the mid-80s when I learned the Universe was something like 10-20 billion years old based on our estimates of the Hubble constant from the decade before. I was in high school in the late 80s and early 90s when we used the CBR measures to estimate 14 billion. I was in college when that was refined to 13.7 based on supernova data. That's been tweaked a bit here and there but mostly remained stable.
Yes, there would need to be much, much more study and evidence to change the accepted age of the universe. JWST has shown some "problematic" galaxies as the article notes, so it may indeed be true the universe is older than originally thought, but we aren't there yet.
... based on an... "interesting" model for the red shifting of light.
> Zwicky's tired light theory proposes that the redshift of light from distant galaxies is due to the gradual loss of energy by photons over vast cosmic distances. However, it was seen to conflict with observations. Yet Gupta found that "by allowing this theory to coexist with the expanding universe, it becomes possible to reinterpret the redshift as a hybrid phenomenon, rather than purely due to expansion."
> The concept was first proposed in 1929 by Fritz Zwicky, who suggested that if photons lost energy over time through collisions with other particles in a regular way, the more distant objects would appear redder than more nearby ones. ... Despite periodic re-examination of the concept, tired light has not been supported by observational tests and remains a fringe topic in astrophysics.
> Tired light theories challenge the common interpretation of Hubble's Law as a sign the universe is expanding. It was proposed by Fritz Zwicky in 1929. The basic proposal amounted to light losing energy ("getting tired") due to the distance it traveled rather than any metric expansion or physical recession of sources from observers. A traditional explanation of this effect was to attribute a dynamical friction to photons; the photons' gravitational interactions with stars and other material will progressively reduce their momentum, thus producing a redshift. Other proposals for explaining how photons could lose energy included the scattering of light by intervening material in a process similar to observed interstellar reddening. However, all these processes would also tend to blur images of distant objects, and no such blurring has been detected.
> Traditional tired light has been found incompatible with the observed time dilation that is associated with the cosmological redshift. This idea is mostly remembered as a falsified alternative explanation for Hubble's law in most astronomy or cosmology discussions.
The article really should not have even mentioned tired light. It's not really what Gupta is proposing. He is instead proposing that Dirac was correct about some things we view as constants not actually being constant.
> Scientists have confirmed that just 1.5 billion years after the Big Bang, time ran five times slower than it does today, 13.8 billion years later. Though scientists have long been aware that conditions just after Big Bang were radically different than those in the cosmos we see around us today, the discovery shows that time is relative in regards to the age of the Universe, too, just like Einstein predicted.
He isn't proposing steady state. He's basically saying that Dirac might have been right in proposing things like the gravitational constant or fine-structure constant are time variant over long enough times. If what we think are constants, aren't, anything is possible.
I don't care. If he's tossing in tired light anywhere, the CMBR won't look like it does. Once you lose the match of density to temperature, you don't get it back.
"While tired light (TL) models have been shown to comply with the JWST angular galaxy size data, they cannot satisfactorily explain isotropy of the cosmic microwave background (CMB) observations or fit the supernovae distance modulus vs. redshift data well. We have developed hybrid models that include the tired light concept in the expanding universe."
He sure has a lane. He's staying in it. Aiming for a coefficient on one coupling constant or another or an ensemble ... so far though nothing but \Lambda on the LHS of the EFEs. I'm sure he'll get there. Theres an admirable sort of methodicalness to his publication record, e.g.:
and honestly I don't hate it. And his institution (byline at the link at the very top is "by Bernard Rizk, University of Ottawa"; turns out he's a Media Relations Officer there [1]; great journalism, phys.org) hyping an adjunct's paper is novel.
> That's the pop science article author's attempt to relate his work, I think
Spoiler, the byline at phys.org is a media relations officer at Gupta's own university. I bet they talked before the MRO the magic "push PR to phys.org" button.
Ok, gigs, I'll bite. I'm afraid I'm already snarky by the start of the abstract. Why are you waving this preprint around, it doesn't say what you say it says (it's mostly just simple algebra and hey did you know we can put coefficients in front of things)? Also I kinda feel bad kicking an adjunct's paper when it's not his fault you've raised his work here. Also, the paper isn't in itself bad.
It's a null result, great. Er er, did I say preprint? It's in MPLA (Mod Phys. Lett. A, if you wanna be all ISO 4 formal)! https://www.worldscientific.com/doi/10.1142/S021773232250155... Ok, not a particularly good physics journal, but at least it's real (I think; people's opinions on world scientific open access fees vary. Todays article processing charges are... USD $2200, but hey, institutional discounts, call for details like when buying from IBM in the 1980s).
"We have attempted to permit concurrent variation of c, G, h, and k in our cosmological, astrophysical and astrometric studies: G~c^3~h^3~k^{3/2}." Concurrent. Concurrent. So great, what's the time relationship?
"Let's assume that the coupling constants evolve with the expansion ... as follows: Speed of light: c = c_af_c(a)" Each constant gets the today CODATA value multiplied by some unknown function of a (the scale factor) on that value.
Ok, cool, so what are the functions? [Spoiler: they could just be everywhen 1. Spoiler: that's what he concludes. Spoiler: you can stop here, really.]
Before going into the functions, he first considers supernovae without seeing the functions.
Ok, this is a draft. I will make a typo or two in this commment just out of solidarity.
Draft? Oh, it's in MPLA! With the typo. https://www.worldscientific.com/doi/pdf/10.1142/S02177323225... (just below eqn (1) on the fourth page). <sarcasm> Good catch, editors and reviewer two! </sarcasm> I DO NOT FEEL BAD ABOUT KICKING THEM. Booooooo! Partial refund to the author and/or his institution.
Eqn 2-4, Some of the functions on the constants are determined by an unknown function on c.
Eqn 5 repeats the relation I quote at the top.
"As pointed out by John Hunter (personal communication) the above can be represetned in terms of the variation of the length dimension of each constant ... if a quantity Q has a length dimension of n, it's f_Q(a) = f(a)^n". [bookmark1] Ok, so generalize and put some meat on the "concurrently".
Hey, fascinating, reviewer two has caused the entire paragraph in the preprint (at link you supplied) to not be in the published version (p. 5 just before the start of section 3). John Hunter is also not in the published Acknowledgments section.
Some words about measurement of mass, and aha, "the Kibble balance test mas m is proportional to h/c^2. Then using equation (5) m \propto f(a)^0 resulting in \dot{m} / m = 0."
4. Discussion
"if we do not permit one of the coupling constants to vary, the others are naturally constrained not to vary" more on that in that paragraph.
This result, which I do not think section 2 proves, is actually pretty important. If it were proved, and also the assertion at [bookmark1] were proved, it would kill off adaptations of current theories which put a function on any constant with a length dimension, which is commonly done [bookmark2 below].
"The approach we have taken is rather phenomenological". Well, yes. Ra-ther.
"A more appropriate and satisfying research would involve writing an action for the interrelated constants represented as fields and derive the relationshop between <constants> with the scale factor a". Right, which is how everyone actually does it. For example DSR <https://en.wikipedia.org/wiki/Doubly_special_relativity>, SME <https://en.wikipedia.org/wiki/Standard-Model_Extension>. Nice to know that Dannenberg has talked Gupta into looking at approaches like that. Pretty sure such things are taught out of his department; if not, he could just drive a couple hours down Autoroute 50 and choose a language.
"... it is not an easy task and we have initiated collaboration for this challenging work."
Great.
Now, he does mention Dirac but not as often as you do in the comments on this article; Dirac proposed varying G for reasons. Gupta argues you can't vary just G, so he disagrees with Dirac.
As to tired light, which was mentioned in this thread, this paper doesn't say much about it. Back to §4's idea about actually writing down an action and deriving the relationship between the constants and the scale factor. In this paper, the relationship is not put forth. At best the author admits the studies of the international prototype kilogram aren't good evidence (and went the wrong direction, "We expected this tiny mass loss could possibly be accounted for using the interrelatinoship among the constants. We have shown this is not possible ..." and his tiny amount of supernova data can be explained by "alternative models". Nice. The standard model is alternative.
Wouldn't this have profound implications for Drake's Equation? If the universe is that much older, then heavy elements have likely been around much longer. If that's true, then the Solar system is much younger than it was yesterday, relatively speaking...
Not really. Many of the Drake equation numbers have enormous error bars.
Which means that the result goes from "We don't really have any idea" to "We don't really have any idea, times two". I suppose you could think of that as a big update to your prior, but it's no change at all to your confidence, which still runs from (0, 1).
At this point it's reasonable to assume the great filter is ahead of us. Even in the "13-billion-year-old universe" scenario, even a 1% head-start gives another alien species time to colonize every habitable planet in the galaxy thanks to the miracle of geometric growth... if interstellar colonization is at all possible.
I think the ideas about needing our seeds spreading across the universe made us very narrow minded. My theory is that the desire to do that is eliminated with advanced enough tech. Say they can create their own universe, dimensions/ virtual worlds/ transfer consciousness/ live forever/etc witch would go against us expecting alien species populating every corner
That assumes that they want to colonize and that our definition of "habitable" matches is close to their own. Perhaps the most common form of intelligent life likes to live without oxygen. Requires very light gravity. Or has a temperature range widely different from our own.
I'd assume that if they wanted to spread out, they'd probably have the ability (like we do) to scout out a solar system before sending a ship. Maybe our 8 planets don't have anything of value for the species looking.
We can ignore all those cases. Because the fact is that carbon-based oxygen-breathing mostly-liquid-water lifeforms must exist out there since they're the only kind we're aware of. And if exotic life does not interact with carbon/oxygen/water life, then those other aliens can still expand freely. And so they should be here already.
If you look at what we know about the history of the earth's atmosphere it went through a phase of high sulfur dioxide, then carbon dioxide, then oxygen rich, then what we have today. A very large portion of that was controlled by the specific life that evolved here. It's almost a fluke that we have an oxygen rich atmosphere. There are so many adaptations that could have happened to deal with the various stages of our atmosphere.
All we know is it's possible for intelligent life to evolve under these specific circumstances. What we don't know is if these are the only circumstances or if these circumstances are particularly common.
What is carbon/oxygen/water life is the only type of life capable of developing intelligence? What if that circumstances that lead to a carbon/oxygen/water rich environment only happen once in a galaxy? And what about the other elements? What if something like iron is, in fact, super rare in the universe on a planet with water/oxygen/carbon. Could you imagine how that might impact the technological growth of an intelligent species? Could you imagine what humanity would look like if the iron age was simply impossible due to a lack of iron?
Intelligence is also a weird evolutionary fluke. Maybe there's life on other planets, but the earth went over a billion years with animals before it finally developed a species with intelligence. Whose to say that nat 20 gets rolled often or at all?
Then there's the sad possibility that interstellar civilizations are simply an impossibility. It takes too many 1000s of years to colonize anything and so no species has tried.
There are just so many factors and the likes of the Drake equation seem to just handwave it all away in a neat little broad overgeneralization.
Why assume it's ahead of us? That would be assuming there are many intelligent civilizations in the local observable universe, facing challenges that are much more insurmountable than the tiny chances of abiogenesis and development of intelligent life. Interstellar colonization sounds hard, but when you include possibilities like self-replicating probes and AI, it doesn't sound so impossible to expect no intelligent life to have managed it yet in a well-populated universe. The possibility of the great filter being behind us (life, complex life, or intelligent life is exceedingly rare) still makes a lot of sense.
An industrial and expansionary civilisation which came into existence anywhere in the Milky Way 10 Mya, and whose interstellar travel was limited to 0.01c, would’ve colonised Earth while we were still in the process of losing our body fur and interbreeding with Neanderthals.
This is fairly recent compared to the age of the universe, and the speeds can be achieved with know (albeit expensive) human technology.
If the aliens had self replicating probes (of the robotic kind, not the organics-in-factories kind), the known rules of physics suggest that a Dyson swarm can be built in less than a century, at which point (0) now you have to ask why there are stars to see, and (1) 0.9c is easy, as is going intergalactic, so such a civilisation can’t have been that recent in half the Council of Giants either.
That we can see stars and that we exist, says that expanding industrial intelligences like us, either never got to this stage, or are filtered in what currently looks like a small gap between here and there.
Misaligned AGI that doesn’t want to expand could be one, so could in-fighting necessarily becoming too easy at the same time as any tech for interstellar expansion.
Personally, I think there’s dozens to hundreds of small-ish (think factors of 0.95-0.10) filters, some ahead, some behind.
Why does everything you imagine look like dust? Shouldn't civs advanced enough to build Dyson Spheres have figured out building materials better than those in the Titanic? That pressure is similar to or stronger than those found in outer space.
They should at least be strong enough to withstand an asteroid hit, and those don't just disintegrate into space dust quickly.
Space Junk is already a problem for us in our present state of advancement. There's space debris from the 50s out there. Why isn't that dust?
Just like evolution doesn't happen suddenly, civilizations don't just disappear. And if the universe is so vast and old, we should be seeing civs in transition, like ours.
There's the argument of the dark forest that everyone is in hiding, but accidents happen, right?t Karma. Why don't these UFOs ever make mistakes? Why don't we see the predator civs? Where's all the noise in the universe? Shouldn't there be massive explosions from all the space wars?
I think it's more interesting and a lot creepier that we are alone in the material universe. Of course, this line of thinking leads to God, and that's poison for the "open-minded".
I think your sense of scale for time and distance needs recalibration.
Billions of years for structures of old to break, not just for civilisations to arrive. It's enough time for planetary atmospheres to boil off into space.
> Shouldn't civs advanced enough to build Dyson Spheres
Kessler cascade.
But, once they're actually that big, I think their only possible downfalls are fratricidal conflicts; so my thinking and comments here are mainly regarding pre-Dyson civilisations.
Further aside: on this scale, one thing I want to find out but don't know who to ask, is "how fast do iron and aluminium sublimate in a vacuum at 300 K?"
> They should at least be strong enough to withstand an asteroid hit, and those don't just disintegrate into space dust quickly.
Asteroids come in many sizes, up to "moon"; moons also disintegrate under gravity when they pass the Roche limit, and for other reasons; the rings of Saturn are young on such timescales, 10 million to 100 million years old.
Now I think about it (in favour of your position, but again I'm assuming filters other than fratricide have to happen before Dyson swarms) an expansive civilisation that Dysoned up 10 Mya inside the Milky Way should've turned the galaxy into one of red dwarfs even if the spheres have since disintegrated.
> Space Junk is already a problem for us in our present state of advancement. There's space debris from the 50s out there. Why isn't that dust?
Remember this is in the context of what we can see looking out into the cosmos.
Our space junk is indistinguishable from dust at lunar distance, let alone interstellar.
And 50 years? Every beat of your heart is to your lifetime what 8 Earth years is to the lifetime of Sol.
> civilizations don't just disappear
Yeah they do. Heck, entire species disappear.
> And if the universe is so vast and old, we should be seeing civs in transition, like ours.
Only with sufficiently good telescopes. The actual ones we've got? It's noteworthy when they've got the capacity to resolve stars as more than single pixels.
I don't ned to recalibrate anything. What I need to do is stop arguing about UFOs and electric cars in this forum. The Fermi Paradox is based precisely on the time and scale of the universe.
"he Fermi paradox can be asked in two ways.[note 1] The first is, "Why are no aliens or their artifacts found on Earth, or in the Solar System?". If interstellar travel is possible, even the "slow" kind nearly within the reach of Earth technology, then it would only take from 5 million to 50 million years to colonize the galaxy.[26] This is relatively brief on a geological scale, let alone a cosmological one. Since there are many stars older than the Sun, and since intelligent life might have evolved earlier elsewhere, the question then becomes why the galaxy has not been colonized already. Even if colonization is impractical or undesirable to all alien civilizations, large-scale exploration of the galaxy could be possible by probes. These might leave detectable artifacts in the Solar System, such as old probes or evidence of mining activity, but none of these have been observed.
The second form of the question is "Why are there no signs of intelligence elsewhere in the universe?". This version does not assume interstellar travel, but includes other galaxies as well. For distant galaxies, travel times may well explain the lack of alien visits to Earth, but a sufficiently advanced civilization could potentially be observable over a significant fraction of the size of the observable universe.[27] Even if such civilizations are rare, the scale argument indicates they should exist somewhere at some point during the history of the universe, and since they could be detected from far away over a considerable period of time, many more potential sites for their origin are within range of human observation. It is unknown whether the paradox is stronger for the Milky Way galaxy or for the universe as a whole.[28]"
The biggest of the past: the relatively thin crust that allows non-catastrophic volcanism, the dual composition of the crust so we have both oceanic and continental plates and the right amount of water to get both massive oceans and not so much as to be a water world, surviving the oxygenation catastrophe, evolution of multicellular life/Cambrian explosion, that the various inorganic carbon sinks and sources are balanced well enough for billion year evolutionary history, that we’re cooperative enough to work together while being competitive enough to develop new tech for “our side” (too little competition and we’d have stopped in c. 1860 tech and communism; too much competition and we’d be at each other’s throats and not be able to sustain global supply chains needed for modern computers).
Arguably the Moon is a big part of many of these things.
My best guess for the future: as we get more tech, it gets easier for individual insane people to blow up important things and/or kill lots of people. AI (never mind AGI/ASI) is just one of many such technologies that make this risk bigger, but even just sufficiently cheap electricity and manufacturing makes it (relatively) simple to use a cyclotron to enrich uranium.
The only way I can see past that is a ridiculous and unpleasant level of surveillance that you need some kind of AI to be able to achieve in the first place, with all the downsides that come with that surveillance, and that’s still the case even if you’re “only using the surveillance AI to find and section dangerously insane people, honest”.
> My best guess for the future: as we get more tech, it gets easier for individual insane people to blow up important things and/or kill lots of people.
I've been saying this recently. I think EM or similar could potentially take and defend a big area with the massive number of drones he could buy or build companies to produce. And that's without inventing any new tech, just mass producing specialized drones.
That's scary enough, but then imagine some small nation-state you've never thought much about, that has all that manpower and collective wealth, and maybe some ambition...
Tech is able to concentrate a big amount of power into a very small number of hands.
Sounds like we’re on the same page. As I’ve thought about this, I can’t escape the disorienting feeling that many more filters are in the past than in the future (and ones with worse probabilities are in the past too). Do you perceive the same? And does the cumulative probability of future filters seem smaller than the cumulative probability of past filters?
Given all the exoplanets with no signs of life, either abiogenesis is probably very hard or life is very fragile (~1e-3 or fewer planets will both develop life and retain it for long enough to pass through an oxygenation catastrophe, but that's squished several filters together).
Difficult to do more than guess past filters beyond oxygenation given the sample size of n=1.
Future? All unknown-unknowns. Even if you rule out paper-clipping-AI-gone-wrong scenarios by assuming only weak and narrow AI slightly less than we have today, the mere ability to get a million colonists to Mars, even with just SpaceX's Starship, requires enough space industry to be a direct military threat to Earth.
But even if these fruits didn't come of it, something doesn't have to be "productive" or useful according to your definition to justify its existence. Just like art or music doesn't have to be "productive," useful or even beautiful by your definitions to exist.
There is more to human existence than breathing, eating and leaving bad comments on websites.
I'd rather have a billion dollars of art installments than another giant telescope. Or a billion dollars of art installments and a billion dollars of welfare, that'd still be much cheaper than the JWST alone.
Are there any relatively recent societal benefits? These all seem 20+ years old. At first I was thinking it might be because NASA's budget got smaller since the 70s, but it's actually increased slightly.
I think it's completely fair to see astrophysics as somewhat vain. The comparison to art is apt - it's essentially a luxury. And the fruits are somewhat of a bad defense, IMO. Besides satellite technology, they're basically side benefits, not something the money was actually spent for. Presumably if the same amount of money was spent on "make something useful to society" there would be higher yield to society than what we got from "get a rocket to the moon" and "make a better telescope". That being said, satellite technology is incredible and I'm glad we have it.
Yeah, down with Big Telescope. This thing goes all the way to the top.
In all seriousness, no portion of my tax payer dollars make me happier than the money that goes to the ISS and JWT and other expensive sciency things in space
Astrophysics can’t take credit for satellites and GPS those were built with the primary incentive of guided munitions and have little to do w outer space. The field has become something like a crossover between a religion and a cheap tabloid
I would almost be willing to bet that in 5 years, the consensus will be much closer to the tradition 13.7 billion years, rather than than 26.7 Billion years.
I am not a physicist, but my understanding was that multiple different ways of calculating age converge toward the traditional number. For his new estimate seems to be using theories that are still at the fringes of mainstream physics. Based on this, my bet would be on the traditional number.
The convergence is only valid if the distance ladder is accurate. There are a variety of deductive bottlenecks in the distance ladder which could implicate the whole current distance model. Standard candles and redshift measurements are calibrated together, for example. If either is off then the whole current ladder could be invalid.
See [1] for a less revolutionary possible solution to the 'Impossibly Early Galaxy Problem', namely, that the initial mass function [2] (distribution of masses of newly-formed stars) was different in the early universe, mainly due to the higher ambient temperature.
IANAP but I'm skeptical at any theory that revises the age of the Universe by a factor of 2. It could be the case but the bar is pretty high for such a massive revision.
One thing about a lot of this from the Big Bang to black holes is that a lot of it makes sense as mathematical concepts but doesn't necessarily translate to something intuitive.
Example: the Big Bang is often described as the Universe starting from a single point. That's an attempt an intuitive explanation but here's another based on the maths. In maths you have the concept of a space that has certain properties. A metric space is a type of space that has, well, a metric. What is a metric? It's a function that defines the distance between two points. So at the start of the Universe, it's more accurate to say the metric between all points was 0. Does that mean it started from a single point? No one really knows. But the metaphor arguably confuses the issue.
One issue is the question of whether or not the Universe is infinite. This is an open question in cosomology. Many suspect it is based on spacetime being incredibly flat based on all our observations. But if you assume the Universe is infinite, how do you reconcile that with the Universe starting from a single point? How does something intuititvely finite become infinite? It sort of breaks down. Simply saying the metric was 0 is less problematic (but also less satisfying, in a way).
There's an awful lot of evidence for the current age estimate. Expanding that by another 13B years should yield a bunch more stellar objects in the expanded age range. There is AFAIK only one such object we've detected, which the article mentions, the so-called Methusalah star [1], which was originally dated at ~16B years [2].
What's more likely: one object is incorrectly dated or the Universe is twice as old as all observations to this point have suggested? I know where my money is.
I don't know how many of you have looked at age estimates for both the universe and the earth over time. What to me is an interesting observation is that an age is calculated on "best" information at the time. Then comes along an anomalous set of observations that do not conform to the then age calculated.
To correct this, a new age is calculated which then pushes back that start time.
It seems to me that we have an essential problem here in that whatever metrics we use to calculate the start event time, something will come along which upsets that apple cart.
Mayhaps, we need to look at the various methodologies in use and see what alternatives might be a better fit for the data we collect. It seems to me that these age calculations are based on a number of unverifiable presuppositions.
It might be better to say that we just do not know as we keep getting anomalies that throw whatever estimates we have into doubt, instead of stating with the current confidence that we do.
Just because we do not know now, does not mean that we won't develop the tools at a later date that will clarify the problem. Being honest that we do not know should never be a problem for anyone. It should be an opportunity to rethink the matter and try something else to see if we can solve things another way.
Engineering has to deal with this kind of dilemma and though it may take decades or longer to develop the understanding of why something works or does not work, many times understanding does come even while using the techniques in the mean time.
> Zwicky's tired light theory proposes that the redshift of light from distant galaxies is due to the gradual loss of energy by photons over vast cosmic distances. However, it was seen to conflict with observations. Yet Gupta found that "by allowing this theory to coexist with the expanding universe, it becomes possible to reinterpret the redshift as a hybrid phenomenon, rather than purely due to expansion."
Aww, the light needs a little nap. No wonder we ( potentially ) got it wrong...!
Where's the energy going, supposedly? I'd assumed "the light's losing energy" had been firmly ruled out long ago—it was a potential explanation that occurred to me the very first time I heard about the observed red shift of distant galaxies, so I figured it must be very and obviously wrong if I'd never heard an actual physicist even mention the possibility of that as a notable factor.
[EDIT] Wikipedia "Tired Light" article:
> The concept was first proposed in 1929 by Fritz Zwicky, who suggested that if photons lost energy over time through collisions with other particles in a regular way, the more distant objects would appear redder than more nearby ones.
Oh, so, what I might have guessed, "it hits stuff sometimes".
Article goes on to make it seem like there's a lot working against the notion, including that distant images ought to be a lot fuzzier if light's interacting with other stuff along the way.
Zwicky's tired light theory proposes that the redshift of light from distant galaxies is due to the gradual loss of energy by photons over vast cosmic distances.
Wouldn't this being true require upending half of what we know about the nature of photons?
I am so old that I remember the Age of Universe as being at 2.1 billion years old.
And that I used to visualize the Sun and our solar system doing the multiple corkscrew through space going in from one arm of our spiral galaxy to the next arm of our galaxy.
Ok. I’m a novice in this. But isn’t time relative, and also affected by gravity and velocities? When we talk about the age of the universe, from which perspective are we considering it?
Indeed time is relative. But, the observed distribution of matter in the universe turns out to single out one particular frame of reference (= large scale spacetime coordinate system). Namely the one in which the CMB radiation is isotropic (same in all directions, neither red shifted nor blue shifted). It is with respect to this particular reference frame that the “age of the universe” is defined.
From my poor understanding of a Physics degree: the "age" is just counted from when everything existed in the same space, before it's rapid expansion. Although, can you say it expanded? It didn't expand into anything because space does not exist outside of the universe. Or do we say it 'expanded' because the distance between the constituent parts inside of the universe grew? It's not good to think about really.
It's always seemed wrong to me that the age of the Milky Way and the age of the universe where about the same. Older universe seems intuitively correct.
This reads like wishful thinking -- "The universe can't be expanding that rapidly, then galaxies outside of the Local Group will leave the cosmological horizon in 100 billion years! Surely redshift must be a lie!"
Compare that to the size of the observable universe which is a sphere with a diameter of 5 x 10^23 kilometers.
Or to the number of stars in the observable universe - 200 x 10^21. One star / (roughly corresponding) solar system is unimaginably huge and then there's so many of them.
In comparison to some of these other measures, the age on the order of 10s of billion years seems actually surprisingly modest.
From the articles' description, it sounds like a hodgepodge of discredited ideas. Maybe unsurprisingly: If you add _all_ of them, you get enough wiggle room to evade observational constraints...
Isn’t that a dead giveaway? The universe expanded outwards at the speed of light from a central point…the radius is 21.5 billion lightyears and the diameter is 43B.
I'm pretty sure the 43B is the radius. The diameter that we can see is 93B ly according to Wikipedia.
The universe is expanding which means we can see more than the age of the universe. The light from far away was carried long as the universe expanded which makes it look like traveled faster than light.
From what I know about academia and the people who occupy positions within it, who function solely to gatekeep progress and then ship the bare minimum to keep their privileged positions, I look at articles like this one and roll my eyes.
Gatekeep progress? Dude, it's cosmology research. What kind of progress are they keeping from whom?
As for shipping the bare minimum, academia has too many smart people competing with each other over too little money. I'd hazard a guess that the "bare minimum" as represented by this paper is considerably higher per dollar than the bar set by someone who uses the word "shipping" to describe publishing.
It is my understanding that the density of the universe billions of years ago was radically different from the one we now observe, and since density is intrinsically tied to our perception of space and time, wouldn't it make more sense that time actually stretches infinitely the further back we go, thus nullifying the concept of a beginning?
I guess I'm having a hard time with the idea that space-time could be discontinuous.