A statute is an act of legislation, and a "statute of limitations" typically prevents courts from dealing with claims arising from matters that happened years ago (subject to some exceptions). The public policy arguments are usually that witness memories decay to the point of obvious unreliability, and that the maxim "equity aids the vigilant not those who sleep on their rights" was already the root of the common law doctrine of laches, but scattered over so much case law that putting the concept on a statutory footing is useful for the courts and all litigants (and especially defendants).
(In criminal law, "justice delayed is justice denied" and clarifications of constitutional or treaty requirements for speedy trials also can be tidied up by the legislature in a statute of limitations).
Statute (legislation) is a superior source of law to contract law, and so there is generally no way to contract to avoid being statute barred if a claim for breach of contract (or specific performance, etc.) is made beyond the statutory deadline.
Typically there are carve outs enacted in a statute of limitations that allow a claim to be brought out-of-time if the defendant has acted in a dishonest way that prevented a claim from being filed in time, for certain classes of litigant, or for certain types of claim. (And in criminal law, for certain offences - serious crimes will tend to have a longer, or no, limit on how long after the crime the prosecution is begun).
A statute of limitations typically does not extinguish defences based on the lapse of too much time; but such defences in some jurisdictions may be contracted away, leaving the statutory limit as the hard deadline.
In a Lorentzian manifold like the spacetime of special relativity (which we'll focus on here) nonzero tangent vectors at spacetime point p (i.e., for any curve passing through p) can be in three separate categories: spacelike, null, and timelike. Details <https://en.wikipedia.org/wiki/Causal_structure>. Curves that physical objects travel are typically timelike at every point (for objects with inertial mass) or everywhere null (for objects with no inertial mass). When unaccelerated, i.e. in inertial motion, rest mass determines whether the object is on a timelike geodesic or a null geodesic.
Four-velocity is defined on a timelike geodesic - its four functions take proper time as a parameter.
Proper time is a parametrization of a timelike geodesic which has several useful properties: it is monotonic allowing for orientability, and gives a unique real value for every infinitesimal point on the geodesic. This in turn means the tangent vector is preserved when parallel-transported along the proper-time-labelled timelike geodesic, with the gross physical meaning that the direction and speed of travel (in local forward/left/up coordinates for example [1]) does not change as proper time advances.
But we can label any curve -- or segment of a curve -- any way we want as coordinates are not physical. It's just that proper time is exceptionally useful as a coordinate. In particular, it satisfies the geodesic equation, gives us a four-velocity, which multiplied by the object's Lorentz-invariant mass gives us a four-momentum.
Unfortunately proper time is undefined on non-timelike geodesics, so can't be used for light, which in vacuum is always on a null geodesic.
However, there are functions that have the same features as proper time, namely monotonicity, uniqueness, and the preservation of the parallel-transported tangent vector. These are affine parametrizations. Proper time is an affine parametrization for timelike geodesics, and is usually denoted τ; null affine parametrizations which satisfy the geodesic equation are usually denoted λ.
We just can't use τ on null geodesics, since it is zero everywhere along one (so non-unique, and non-advancing). Statements based on the use of τ like "light experiences no time" or "light's path is infinitely length-contracted" improperly imply the use of τ.
However, if we use affine time λ, we get uniqueness, monotonicity, and the preservation of the tangent vector under parallel transport. The first derivative with respect to affine time at a point on the null geodesic lets us define a 4-momentum so we can use the Planck-Einstein relation E = pc = hf = hν = ħω relating the frequencies and wavelengths of photons, and how they redshift and dilate from point to point. (This is especially handy in curved spacetimes, like the expanding one in cosmology or the collapsing one around black holes).
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[1] An image may help: drop two dimensions from 3+1 spacetime to give us 2-space we get a tangent plane instead of a tangent volume at each point along a geodesic on a 2-sphere (which meridians on Earth's surface approximate) <https://en.wikipedia.org/wiki/Local_tangent_plane_coordinate...> -- sliding the tangent plane south along the meridian in uniform motion is like advancing the proper time.
is wrong. A photon has a momentum, which can increase or decrease as it travels through free space.
Using general relativity, it's straightforward to define an affine time on a null geodesic (even if one cannot define a proper time on one), and a momentum that is a function of the affine time at each point.
The Lyman-alpha forest is a straightforward "laboratory" for this approach, which can calculate the Lyα absorption lines seen when a bright distant quasar or luminous Lyα emitter has atomic hydrogen clouds between the distant source and us (the absorption lines indicate photons with a very narrow range of momenta participated in hydrogen atoms' electrons transitioning from ground to the first excited state, with the later relaxation photons radiating in random directions). The pattern of such dark spectral lines tells us how redshifted the background light and earlier absorption lines are at each gas cloud along the way.
Peer reviewers don't generally reproduce the work in the publications they are asked to review, at least not during the review process itself. Neither do journal editors.
If you want a real vanity press, check vixra and its origin story.
ArXiv does have moderators and endorsers in each area, although they are usually light-touch, weeding out literally unreadable submissions, ones that so obviously ignore formatting guidelines that it beggars belief they could comply with a typical journal's rules, and ones that are clearly submitted to the wrong area.
Having a stable document early (a pre-print) tends to widen the scrutiny of papers that may ultimately be published to a journal whose editor's expertise lies in a very different area from the submission; this can and does lead to author corrections being made before journal publication.
There are plenty of peer-reviewed papers which are hot garbage that have found their way into prestigious high-impact journals like Nature and Science (see <https://retractionwatch.com/the-retraction-watch-leaderboard...> for examples, and note none of the top 10 are in areas covered by the arXiv).
> being published by a famous professor from a prestigious university is also no guarantee
Everyone in academia knows this, including the vast majority of famous professors from prestigious universities, because of online repositories like <https://retractionwatch.com/retractions-by-nobel-prize-winne...> (and much more sadly because of <https://en.wikipedia.org/wiki/Nobel_disease>, lower-profile versions of which academic paper-writers -- and dissertation writers -- tend to encounter as they chase the history of the problem before them or read late citations to works they are relying upon). This particular part of your set of claims is is not a real problem in academia or with the arXiv in particular.
Finally, what value does publication in a predatory journal bring? Do you believe that peer review and editing were actually even performed in the majority of MDPI's most predatory journals, for example? <https://www.predatoryjournals.org/news/list-of-all-mdpi-pred...> Some papers published in some of their pay-for-publication open access journals don't even get submitted to the arXiv; one might hope this is out of embarrassment by the authors, although the (low) bar set by the arXiv itself is certainly a factor.
The remedy for a reasonably argued but wrong academic paper isn't lack of publication, failed peer review, or editorial alteration, but rather reply papers. That's the academic dialogue.
Thanks for this reply, your points are well taken and it really got me to think about this stuff.
I suppose you could view arxiv as being a way to let more people do a peer review on the papers, i.e. as one component of a more open and transparent peer review process. As such, it is certainly a welcome alternative to what the snootier journal reviews do, which is to put off reading your paper for a year, and then spend about 50 seconds looking for a reason to say "no".
But I had a narrow point to make when I said that arxiv is a vanity press: just because something is on there doesn't guarantee that it is correct, or even useful. It is a vanity press in the sense that it will publish pretty much anything--modulo obscenity and porn laws, and apparently also some sanity checking by arxiv moderators--but so does a vanity press for print books.
To your point of predatory journals, power-broker reviewers and such, yes, I have done my fair share of suffering from them. It slows down good research and passes through bad research. The system is badly in need of reform, and arxiv gives a much needed alternative.
But really, the problem is (as one of my profs said) that science is totally run on volunteer, unpaid labor. Peer reviewers are very busy, get paid nothing, it is mostly a distraction. This leads them to look for other ways of being compensated--e.g. the can try to be a power broker, a feared authority, etc.
The real solution would be to actually pay peer reviewers and fund them so they can actually reproduce the results. Here's how it could work: when a researcher submits a grant proposal, they budget for enough money to fund the research and enough money to peer review and reproduce it. If the research isn't good enough to warrant an attempt to validate it, then it isn't worth doing in the first place.
Thanks. Nobody ever admits when they are wrong on the internet, so I'm trying to be the change I want to see.
W.R.T. the grand historical tradition, etc, note that the great majority of people who practiced that were, like Plato, independently wealthy and otherwise idle. Those who didn't need any money.
That's why we give Judges, teachers, and Professors tenure, a guaranteed job for life. People are more likely to be fair judges of other people's performance when they don't need the money.
So I guess if you want a non-conservative fix, it would be universal guaranteed minimum income. Something we already have, BTW, but you have to be over 62 to get it.
We've tried to open it up to more than just the 1%, but we didn't really go all the way. It is really unreasonable to expect somebody who isn't independently wealthy to do free work. It is a lot of work to properly review a paper, and reproducing the results is something you simply can't do at all if you are supposed to already be working 70 hours a week generating your own research.
Of course a researcher paying reviewers would be a disastrous idea. But if the grant-awarding body would hire 3rd parties to validate that their money was actually well spent, I think it would be a win/win.
Thanks for the references on where paying reviewers has already been tried. I'd like to see others reproduce their success :-)
No paper is guaranteed to be completely accurate and correct at the time of publication; the remedy for honest errors is follow-on papers by the original authors or others in the field putting their names to formalized counter-arguments.
This is how the academic dialogue works, and it dates back to early durable records in the ancient world -- about as far before Plato as Plato's Academy is before today's universities. Innovations like academic journals come from "merely" four centuries ago, and pre-publication evaluation by peers about three hundred years ago. Anonymized pre-publication review is more recent still, and publishing schedules (as well as the needs of the submitter to have the submitted work dealt with in good time) don't admit a dialogue over some subtle point a referee takes some issue with. Moreover, such a pre-publication dialogue is generally non-public, and often also filtered through an editor. It can get messy [1].
As I'm sure you've discovered in your own post-secondary education, academia is very conservative (in the sense of "retaining what mostly works, even in the face of mounting scaling problems", foremost among those being the ever-increasing volume of publishable works generated by researchers).
Direct compensation of referees by journals has a number of pitfalls ranging from the fiddly details of how to deal with income tax liability pay (and credits towards future publication fees, etc) incurs to whether it compromises the objectivity of pre-publication evaluation (which is frankly already not very good in highly specialized areas).
Payment of reviewers by paper submitters is imho an even worse idea -- how do you preserve the anonymity of referees (especially with respect to the submitters)? Do submitters or reviewers have exposure to their (probably different) tax authorities for these transactions? (I can think of at least four national tax agencies that would view the received pay as taxable income, and also potentially subject to value-added tax on professional services. One already sees this problem with conference honoraria.)
Another -- one that already exists in the real world -- might be for institutions and grant-funders to build in support for peer review of others' work by project members. To the extent that detailed pre-publication review benefits academia, and societies that fund academia, as a whole, maybe referees should be rewarded (or even obliged) to do paid reviewing duty. One might compare the requirement to do pro bono work imposed on many practising lawyers by their regulating authorities (especially interesting are jurisdictions in which a party losing a court contest to a party represented pro bono usually must pay into a fund that supports the overall scheme).
Personally I think it would be more useful to everyone to have a solid reply paper published in due course than a blocked initial publication. My ideal is that referees aim to help submitters not accidentally professionally embarrass themselves.
Then on your reproduction idée fixe, supporting the generation of papers which confirm reproduction is something that societies could certainly work on. Many incentives to write and submit papers calling out flaws in others' work already exist, and of course could be expanded. I don't think any of that should be done with masking of the participants. Additionally, reproduction of results is often less interesting than (sometimes much) later testing of published results in significantly different ways.
(Indeed, foundational papers from more than ninety years ago are often re-proven by modern-day experiments, both as a side effect of (or opportunity arising from) pursuing the primary research goal, and as a way of testing e.g. new metrology technology, new computational tools, mathematical advances, and so on. Also, some of those foundational papers simply could not be tested with great accuracy with tools existing at the time of publication. Their publication, however, tended to drive the development of such tools, and in modern days such foundational papers are found to be good only within certain limits that could not have been explored closer to the time of publication.)
Yes, during cosmic inflation for example: two test objects initially close can end up many light-years apart. If we make these test objects null (i.e., lightlike) then we can always contrive an inflation that stretches them apart in such a way that they still meet again.
Some exotic spacetimes involving pp-wave sandwiches can focus initially non-converging and spatially distant light pencils onto each other at a caustic shortly after the passing of the stack of plane-parallel gravitational waves. One can hide some such processes in the early cosmos.
Where or encroaching upon what does the univerise expand into? If the universe is all the real estate of physical reality, what is it subsuming as it expands in order to accomodate that growth?
Not sure what level of answer you want here. I don't think there's a good slogan that you could memorize and repeat like "the night sky is black because Olber's 'paradox' is badly formulated in that the universe's star formation has a finite history and radiation from before the first stars is redshifted too low to activate visual opsins" or "matter tells spacetime how to curve", and anyway most such slogans are likely to induce misunderstanding (a major theme of the article linked at the very top).
Here's a sketch for a crash syllabus that would take you closer to an answer I'd write, not being a practiced science communicator:
My approach would be to teach you some differential geometry on a differentiable Euclidean plane (mostly relating the classic Euclidean distance to the integration of a line element), then what a Riemann manifold is, then how a 3+1-d pseudo-Riemannian one differs from a 4-d Riemannian manifold (and understanding the Ricci curvature in an Einstein manifold), and take you to understanding the simplest of metrics on the Lorentzian manifold, and the concept of geodesics and how they separate into spacelike, timelike, and null. I'd also teach you early about affine distance so that you don't stumble into problems understanding that a pulse of light from the ground to a mirror on the moon and back to the ground takes about two seconds, and how a pulse of matter -- including a pulse of light -- loses energy in an expanding spacetime. (That's another where does it go question, and a good one to think about.) Then I'd introduce Raychaudri-equation-style thinking, with a spray of timelike geodesics separating, as a way of understanding the metric expansion of space and the FLRW metric (where each Friedmann-equation dust represents an enormous number of timelike and lightlike geodesics).
I'd also teach you about the Lagrangian and Eulerian specifications of the flow field, and how they relate to one another. We can have a idealized (freely-falling, feels-no-forces) Lagrangian observer follow one line in a spray of geodesics which are initially extremely close to each other, and which separate with the metric expansion of space. Some of the initially-close geodesics causally disconnect from our chosen Lagrangian observer, with close-but-less-close ones disconnecting quickly, and very-close ones staying practically parallel for a very very long time. This is basically the Raychaudri equation, as applied to cosmology. We'd want to explore radar distances between our Lagrangian observer and ideal reflective objects attached to other geodesics on the spray.
We then can relate all that to a spacetime-slicing approach where we track what's on 3-d spacelike hypersurfaces, in a Eulerian style, going from our Rachaudhrian spray to a collection of space-filling dusts or fluids that dilute away differently over time. This is the usual picture cosmology students operate with.
Understanding that, especially how expansion generates several cosmological horizons, is half of the key to answering your question. The other half is understanding that one can run the relevant equations under a time-reversal, with initially enormously distant objects freely falling towards each other and ending up practically on top of each other in the early history of expansion.
Along the way we'd also be talking about the thermodynamics, as expansion is adiabatic.
Our causal physics are all related to an extremely hot, extremely dense, extremely low-entropy volume in our billions-of-years-ago past, which we retrodict by studying fractions of later volumes (fractions as small as careful laboratory experiments and as big as large scale galaxy surveys). Anything close to that patch causally disconnected from us very early, and we'll never be able to hear from those parts of a big spray, and they'll never hear from us.
Just outside our very early universe, things probably look very similar to things just outside it. The logic here is that as our galaxy crosses out of a cosmic horizon of somone far away, our galaxy doesn't do anything weird, and likewise there are many galaxies currently crossing out of our cosmic horizons, and they probably aren't doing anything weird either.
Studies of the expansion history, still-viable cosmic inflation scenarios, and global spatial curvature have led to estimates (e.g. Guth's work) that some our early hot dense patch is at most 10^-23 of basically the same early hot dense stuff. That's fairly comparable to the number of atoms of water in the North Atlantic ocean, all of which are interchangeable, although they all have different histories of where they've been in Earth's oceans, the pressures and densities they've experienced on their travels, and so on.
The pre-inflationary patch's tiny elements are pretty interchangeable although they'll have slightly different histories of expansion, galaxy formation, and so on, given tiny differences in their very early histories ("initial conditions"). Some may be overdense and quickly collapse. Some may be underdense and thus produce few if any stars.
Now, is that primordial hot dense patch embedded into something bigger? Good question! Does it even matter, given that it causally decoupled from us so early? Good question! How do we even begin to investigate that? Good question! That's all live postgrad and postdoc research, with a lot of focus on trying to make the low entropy part of our hot dense early universe seem un-special.
Once you have that under your belt you can join the manifold (pardon the pun) papers exploring the physical implications of various guesses about what's outside the everything-everywhere-everywhen fully determined ("block universe") picture painted by a notional exact solution of the Einstein Field Equations of General Relativity, which we can only successively approximate by sampling signals from our past.
But at least you'd then understand what it means to say that mean energy-densities fall over cosmological time, and that the centres of mass of galaxy clusters are separating over cosmological time, and that our distant distant descendants won't see any galaxies not presently in our local group.
For extra credit you could play around with embeddings of de Sitter space in higher-dimensional manifolds and run into the usual frustrations of it being quite hard to recover known physics -- one can even largely justify a statement like embedding a 3+1d spacetime into a higher dimensional spacetime is generally not possible. Of course, many people still attempt to make that work not so much to answer your question, but to find ways of more easily calculating the way our visible universe behaves.
[*] I'd have maybe said "its own future" and otherwise present a wordier version of what Siegel wrote (explicitly raising time-orientability), but really I'd want to explain why I'm mostly a blockworlder in spite of how us small temporary knots of atomic nuclei feel about that <https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time...> and that maybe the real question is why our brains encode the concept of expansion at all. Anyway our puny brains can't hold all knowledge, we can't just pour in mathematical physicslike kung fu, helicopter piloting, or motorcycle-hotwiring skills in The Matrix movies, and the behaviour of the universe at scales of billions of lightyears didn't change once humans started printing cosmology textbooks. And it's OK if you haven't worked through any of those; just be careful of memorizing factoids from people who haven't worked through any of them either.
The problem is in allowing perturbations around effective w_{DE}=-1. The "phantom divide crossing" is the evolution of dark energy's effEOS across w = -1, the boundary between a quintessence regime (w > -1) and a phantom dark energy (w < -1) regime. Phantom models generically violate the null energy condition. A local crossing thus causes all sorts of problems for minimally coupled single scalar field DE (see e.g. https://doi.org/10.1103/PhysRevD.78.087303 aka https://arxiv.org/abs/0808.3125) as fluctuations of the DE field into the phantom regime must be controlled or offset assuming one does not want the total energy density to be negative. That turns out to be hard.
(In criminal law, "justice delayed is justice denied" and clarifications of constitutional or treaty requirements for speedy trials also can be tidied up by the legislature in a statute of limitations).
Statute (legislation) is a superior source of law to contract law, and so there is generally no way to contract to avoid being statute barred if a claim for breach of contract (or specific performance, etc.) is made beyond the statutory deadline.
Typically there are carve outs enacted in a statute of limitations that allow a claim to be brought out-of-time if the defendant has acted in a dishonest way that prevented a claim from being filed in time, for certain classes of litigant, or for certain types of claim. (And in criminal law, for certain offences - serious crimes will tend to have a longer, or no, limit on how long after the crime the prosecution is begun).
A statute of limitations typically does not extinguish defences based on the lapse of too much time; but such defences in some jurisdictions may be contracted away, leaving the statutory limit as the hard deadline.