They probably do change, but extremely slowly. It would feel strange if there were something fixed in the universe.
From Wikipedia:
The natural reactor of Oklo has been used to check if the atomic fine-structure constant α might have changed over the past 2 billion years. That is because α influences the rate of various nuclear reactions. For example, ¹⁴⁹Sm captures a neutron to become ¹⁵⁰Sm, and since the rate of neutron capture depends on the value of α, the ratio of the two samarium isotopes in samples from Oklo can be used to calculate the value of α from 2 billion years ago.
Several studies have analysed the relative concentrations of radioactive isotopes left behind at Oklo, and most have concluded that nuclear reactions then were much the same as they are today, which implies that α was the same too.Which is why a synthetic clock is needed here. That will have a known inception date and the changes if any can be compared.
The problem with both is they're not exactly fully closed systems anyway so there will be some margin of error ever with the length of the operation.
And during the test, we might just find out something completely unaccounted for in current physics... That isn't a universal constant related at all.
The isotopes produced during the natural nuclear reactor 2 billion years ago were produced in certain ratios because of the relative sizes of their nuclear cross sections, which depend on the fine structure constant.
The isotopes used in radio dating are produced by spontaneous transmutation over time, which is governed by entirely different processes.
This sort of thing tends to be so far from "common sense" it probably doesn't make sense to try to reason about it from that perspective.
The redshift of far away galaxies is calculated multiplying the frequencies by 1+z, so you get the same displacement if you draw the spectrum in the correct logarithmic scale https://en.wikipedia.org/wiki/Redshift
The emission/absorption lines of Hydrogen are calculated using the Rydberg constant https://en.wikipedia.org/wiki/Rydberg_constant that use the mass of the electron. But it's not the actual mass of an isolated electron, you must use the "reduced mass" because the electron moves around the proton but the proton also moves a little [1]. So the reduced mass of the electron is
reduced_mass_electron = 1 / ( 1 / actual_mass_electron + 1 / actual_mass_proton )
The proton is much heavier [2], so the difference of the reduced and the actual mass of the electron is only .1%.
If you magically change the mass of the electron to be equal to the mass of the proton, then the reduced mass of the electron would be 1/(1/1+1/1)=1/2 of the actual mass of the magical electron, and all the lines in the spectrum of Hydrogen will change.
But the spectrum astronomer get includes other elements and isotopes. For example Deuterium that has the same charge but the double of mass. In the real word, the reduced mass of the electron in Deuterium is also almost equal to the actual mass of the electron, the difference is like .05%.
In the magical world where the mass of the electron to be equal to the mass of the proton, then the reduced mass of the electron would be 1/(1/1+1/2)=1/3 of the actual mass of the magical electron, and all the lines in the spectrum of Deuterium will change but in a different way.
I think it's possible to see all these lines in a spectrum, but to be sure ask an expert. Anyway, a magical change to make the mass of protons and electrons equal will change the spectrum of all the other atoms in different and strange and weird and unexpected ways. [3] So it will be easy to spot. Smaller changes will change thing and be visible too, unless they are too small.
[1] If you want to go down the Quantum Mechanics rabbit hole, they don't move and you must use orbitals. But the correction is the same than in the fake/simplified classical calculation.
[2] * massive
[3] A heavy [2] electron is very similar to a muon, and in Hydrogen molecules with muons both Hydrogen are very close so you get fusion reactions https://en.wikipedia.org/wiki/Muon-catalyzed_fusion so the magical would be very strange.
The correct number is
1/(1/1+1/2)=2/3
I incorrectly wrote 1/3 instead.
That is the problem with any argument for some new physics - it might exist, but it can't have much effect or we would detect it. Generally I only see people arguing for new physics because they really want faster than light travel (typically also without all the weird time effects, but a small minority would accept it with time effects)
Since photons move at c, they experience zero time between creation and destruction.
Proper time, τ. But your proper time and my proper time are different, and are only coordinate times, monotonic labels on timelike curves. That means τ is an affine time.
There are other affine times available. And we have to choose an affine time other than τ for null geodesics, the curves which photons (in vacuum) travel along. So, instead of proper time, for photons there's the affine parameter.
The same rule applies: there is nothing special about the affine parameter. I don't have to use a photon's affine parameter when describing physics any more than I have to use the proper time of an ultrarelativistic electron. And I can convert physics done in one splitting of spacetime into space+time to a different splitting of the same spacetime into space'+time'. The coincidences in the spacetime are unchanged by the switch of how we split -- splitting is just a change of coordinates.
If we divide up spacetime into space+time where the choice of time axis along which to order spatial volumes is my proper time, the emission of a photon in the photosphere of the sun and its subsequent destruction in my eyeball happen in a definite temporal order: there is a time delay. There is still a temporal order if we divide up space+time using your proper time, or that of an ultrarelativistic electron.
There are some special technical aspects of dividing up spacetime into space+time using a photon's affine parameter as the time axis, but it's certainly doable. A photon shares a different 3d spatial volume with many other things at each affine parameter labelled point on the photon's curve. Phases of orbits, stages of an elastic collision, and so forth are among the things "snapshotted" into each 3-d spatial volume the photon finds itself in. Those evolve from one 3-d spatial volume to the next to the next.
So returning to the previous picture: if we split up space+time according to the affine parameter of a photon, there will be some 3-d volumes at which the solar photon is much closer to the sun than to my eyeball, and some 3-d volumes where it is much closer to my eyeball than to the sun. The same is true for the solar photon itself: some affine parameter values put it closer to the sun than to my eyeball, and at some affine parameter the photon's journey ends.
If a photon's trajectory is through curved spacetime, there will be a difference in momentum between two points on the trajectory (we are not restricted to the photon's creation or its destruction), which we can calculate using the affine parameter. The physical interpretation is that the photon undergoes a redshift or blueshift between two points in spacetime.
Note that I did not take the lim v->c approach you did in your first paragraph because there are geometrical differences in a Lorentzian spacetime between a null geodesic and a timelike one, even if the timelike geodesic is associated with a speed arbitrarily close to c. The photon is almost always on a null geodesic. A non-massless observer will never be on a null geodesic.
> Since photons move at c
Photons can be made to move slower than c, in which case they are not on null geodesics, and therefore proper time might be suitable for them.
Photons moving at c must be on null geodesics.
Proper time -- one particular affine time -- is undefined on null geodesics. However, they experience a different affine time. One can interconvert, so it does not make sense to say that photons "experience zero time".
Lastly, if the totality of the photon's curve through spacetime is on a null geodesic, the photon won't be able to experience much of the universe evolving around it as it flys away from its creation. However, segments of a photon's curve can be other than null geodesic motion as (for example) they cross through wispy gas clouds or strong magnetic fields in space. Temporarily slowed light <https://en.wikipedia.org/wiki/Slow_light> can in principle receive news of the world. This could have happened for a photon emitted billions of years ago from a high-redshift quasar en route to the JWST.
Extra reading:
https://en.wikipedia.org/wiki/Initial_value_formulation_(gen...
Blau, Frank, Weiss 2006 (section 3 "Brinkmann coordinates are Fermi Coordinates:", 4 "Null Fermi coordinates, general construction", 5 "Expansion of the metric in null Fermi coordinates") arxiv version https://arxiv.org/abs/hep-th/0603109 (link to publication in Class.Quant.Grav. is on the abstract page).
"What is the physical meaning of the affine parameter for null geodesic?" https://physics.stackexchange.com/questions/17509/what-is-th...
> To explain how this actually works without making a math video, we have to make a lot of physicists grumpy, so please keep in mind that we are simplifying and lying a bit.
And that simplification / lie is that everything moves at the speed of light in spacetime. We are moving at basically 0 in the space coordinates and 1s/s in the time dimension (which is "light speed" in the time dimension). However... (1:45 in the video)
> Photons, light particles, move at the speed of light through space. They don’t experience any time passing because their speed in that time dimension is 0. In the time dimension they are frozen in place. If you see light on earth, from the photon’s perspective it was just on the surface of the sun and then suddenly crashed into your eye with nothing happening in between.
... and this falls into the Lie-to-children domain. https://en.wikipedia.org/wiki/Lie-to-children#Examples_in_ed...
It reminds me of my silly One Photon Conjecture. That is, there’s only one photon that pops in an out of space as required by coupling events. Since it doesn’t experience time saying it can’t be in two or more places at the same time isn’t meaningful!
they actually arrive slightly later than neutrinos to observers on earth because neutrinos just plow through virtually anything including stars and planets while photons have to travel the path affected by gravity
photons aren't affected by gravity directly because massless but their path, their limit of causality, is affected
An object at full rest is according to its wave/path equation literally everywhere at all times.
However superconductivity has a bunch of truck sized holes for this. Specifically we don't quite understand Bose-Einstein condensate completely. Funky entities like time crystals appear in the mathematics, etc.
why would you think that neutrinos can magically ignore the curvature of spacetime? completely wrong.
What you seem to be trying to remember is that certain types of extragalactic supernovae produce a tremendous number of neutrinos, and those can be detected on Earth before the associated light does. The reason is that both are produced deep within the dying star, and while the star's outer layers are largely transparent to the neutrinos (not completely: it's neutrino pressure that makes the star explode[1]), the deep-in-the-star supernova photons bounce around inside. That's very much not empty space.
https://www.astronomy.com/science/in-a-supernova-why-do-we-d...
We can detect type SN1a supernovae out to about z=4 (redshift of about four in light-years is about twelve billion years of light travel time from the supernova to us). That's not really enough for the delayed pulse of light to catch up to the neutrinos produced also produced in the dying star's interior at the same time. Also, not all of the emitted photons are likely to scatter off gas and dust in any interstellar medium along the way, so the relative delay at Earth of the bright electromagnetic flash is dominated by the dying star's outer layers.
(There are more complicated electromagnetic signals like light echos <https://en.wikipedia.org/wiki/Light_echo> that can follow on much later; there aren't any neutrino equivalents really).
> photons aren't affected by gravity directly because massless but their path, their limit of causality, is affected
Not sure what you are trying to say here, but photons certainly both feel and source spacetime curvature. In empty space, photons always travel along null geodesics. The distribution of all matter, energy and momentum, the expanding background of inter-galaxy-cluster space, and the collapsing background of galaxy clusters (and galaxies, and components of galaxies like their central black holes and stars) picks out what geodesics fill spacetime. Some are null, and massless things can find themselves on ("couple to") them. Some are timelike, and massive things can find themselves on them.
Geodesics are free-fall trajectories, so are inertial as in "things in motion tend to stay in motion", and barring any further accelerations a photon coupled to a null geodesic will stay on that null geodesic and a neutrino coupled to a timelike geodesic will stay on that timelike geodesic.
Some neutrinos and photons start on parallel geodesics within the supernova's exploding core. Each neutrino stays coupled to its timelike geodesic all the way to detection on Earth. The photons are all forced off their initial null geodesic by mostly scattering off nuclear matter near the star's core, find themselves on a second null geodesic, more nuclear scattering, possibly some scattering off ions in outer layers, and each ultimately might end up on a geodesic that it stays on until it reaches Earth.
- --
[1] on neutrinos driving the explosions and how alot of them stick around as they are captured into heavier chemical elements and isotopes https://www.mpg.de/11368641/neutrinos-supernovae
In fact, based on this we can tell that the fundamental constant the speed of light has not changed which I agree is very strange.
It is possible to eliminate almost all fundamental constants by choosing so-called natural units for the base physical quantities, for instance the elementary charge as the unit of electric charge.
For all fundamental constants that can be eliminated by choosing natural units it makes no sense to discuss about changes of them.
Nevertheless, even when a natural system of units is used, there remain 2 fundamental constants (plus a few other fundamental constants that are used only in certain parts of quantum field theory).
The 2 important fundamental constants that cannot be eliminated are the Newtonian constant of gravitation, which is a measure of the intensity of the gravitational interaction, and a second fundamental constant that is a measure of the intensity of the electromagnetic interaction, which is frequently expressed as the so-called constant of the fine structure.
The meaning of the constant of the fine structure is that it is the ratio between the speed of light in vacuum and the speed of a charged particle with unit charge, like an electron, that rotates around another charged particle with unit charge, which is much heavier, like a nucleus, in the state with the lowest possible energy, i.e. like the ground state of a hydrogen atom, but where the nucleus would have infinite mass. The speed of the rotating particle is a measure of the strength of the electromagnetic interaction between two elementary charges.
So the only fundamental constants for which there could be a evolution in time are those that characterize the strengths of the electromagnetic interaction and of the gravitational interaction (and also the fundamental constants that characterize the strengths of the nuclear strong interactions and nuclear weak interactions).
The values of these fundamental constants that characterize the strengths of the different kinds of interactions determine the structure of the Universe, where the quarks are bound into nucleons, the nucleons are bound into nuclei, the nuclei are bound into atoms, the atoms are bound into molecules, the molecules are bound into solid or fluid bodies, which are bound by gravitation into big celestial bodies, then into stellar systems, then into galaxies, then into groups of galaxies.
Any changes in the strengths of the fundamental interactions would lead to dramatic changes in the structure of matter, which are not seen even in the distant galaxies.
So any changes in time of the true fundamental constants are very unlikely, while changes in the constants that appear as a consequence of choosing arbitrary units are not possible (because such fundamental constants are fixed by conventions, e.g. by saying that the speed of light in vacuum is 299,792,458 m/s).
They are the properties of those particles. There are such properties for leptons, for hadrons, for nuclei, for atoms, for molecules, for chemical substances, for humans and so on.
Any object, either as small as an electron or as big as the Sun is characterized by various numeric properties, such as mass.
The fundamental constants are not specific to any particular object. As I have said, after eliminating the fundamental constants that are determined by conventional choices of the system of units, the only fundamental constants that remain are those that characterize the strength of each fundamental interaction, as expressed in a natural system of units.
Because most objects are composed of smaller subobjects, it should have been possible to compute their properties from the properties of their components. Starting from the properties of leptons and quarks, it should have been possible to compute the properties of hadrons, nuclei, atoms, molecules and so on.
Unfortunately we do not have any theory that can compute the desired properties with enough precision and in most cases even approximate values are impossible to compute. So almost all properties of particles, nuclei, atoms or molecules must be measured experimentally.
Besides the question whether the fundamental constants can change in time, one can put a separate question whether the properties of leptons and quarks can vary in time.
Some of the properties of leptons and quarks are constrained by symmetry rules, but there remain a few that could vary, for instance the mass ratio between muon and electron. It is likely that a future theory might discover that this mass ratio is not an arbitrary parameter, but the muon is a kind of excited state of the electron, in which case this mass ratio could be computed as a function of the fundamental constants, so the question whether it can vary would be reduced to the question about the variation of the fundamental constants.
When you have 10 absolute masses, you can also represent them by one absolute mass and 9 dimensionless mass ratios. Then you can claim that your model has 9 dimensionless parameters, but this changes nothing, because in any formula that relates different physical quantities you must multiply the mass ratios by an absolute mass.
There are cases when using dimensionless mass ratios does not bring any advantage, but there are also cases when using mass ratios can improve the accuracy. For very small things, like particles, nuclei, atoms or molecules, it is possible to measure with much higher accuracy the ratio between their mass and the mass of an electron, than their absolute mass.
So in particle/nuclear/atomic physics it is usually the best to express all masses as dimensionless ratios vs. the mass of an electron and to multiply them with the absolute mass of an electron only where necessary. There are methods to measure with high accuracy the absolute mass of an electron, based on measuring the Rydberg constant and the constant of the fine structure.
Most parameters of the standard model are dimensionless because they are ratios that eventually need to be multiplied with an absolute value for the computation of practical results.
In many research papers about the standard model they get away with using only "dimensionless" parameters because they take advantage of the fact that they cannot continue the computations far enough to obtain practical results, so they use some ad hoc system of units that is not clearly defined and which is disconnected from the remainder of the physics.
What? So, what is the mechanism in nature that produces those 9 ratios? If you haven't got one, you haven't got a theory; you've got to admit that those are experimentally confirmed fundamentals.
So, I interpret what you're saying like this: you have got a pet theory where the mass ratios are calculable from some other, more fundamental assumptions, but (charitably: because the theory is numerically too hard, or you lack compute resources) you don't have the actual means to calculate them.
Otherwise, I scratch my head. If you don't manage to enlighten me, I deem you a crank.
This is just a mathematical manipulation of the numeric values. If you have the absolute masses m1, m2 and m3, you can store instead of those 3 numbers other 3 numbers, m1, m2/m1 and m3/m1. This stores the same information, because whenever you need e.g. m3, you can recover it by multiplying m3/m1 with m1.
You can do the same thing with one hundred absolute masses, replacing them with a single absolute mass together with 99 dimensionless mass ratios.
As I have already said, sometimes there are good reasons to do so, e.g. in particle/nuclear/atomic physics you can increase the accuracy of computations if only a single absolute mass is used, the mass of the electron, for which there are accurate measurement methods, while all the other masses are replaced with dimensionless ratios between the corresponding absolute masses and the mass of the electron, because such mass ratios can be measured accurately based on the movements in combined electric and magnetic fields.
This includes the standard model, where the absolute mass of the electron is necessarily one of the parameters of the model, but all the other masses can be replaced with dimensionless mass ratios, e.g. the mass ratios between the muon mass and the electron mass or between the tauon mass and the electron mass.
Similarly, any parameter used to characterize the strength of the electromagnetic interaction is not dimensionless (in any system of units where the elementary charge is one of the base units, and such systems are better than the alternatives), and one such parameter must be included in the standard model. The parameters that characterize the weak interaction are also not dimensionless, but they can be converted to dimensionless parameters in a similar way with the masses, by using ratios (vs. the electromagnetic interaction) that are incorporated in the mixing angles parameters.
The end result is that the standard model is expressed using a large number of dimensionless parameters together with only a few parameters that have dimensions, because this representation is more convenient. Nevertheless, there are alternative representations where most parameters have dimensions, by rewriting the model equations in different forms, so there is nothing essential about having dimensions or not.
You do still need a term to characterize the strength of gravity. They sometimes use η, which can be defined in terms of G, c, Planck's constant, and a fundamental mass like the electron. The result is a truly fundamental unitless constant.
The Standard Model has a dozen or so other fundamental constants, describing various mixing angles and fundamental masses (as ratios).
The so-called Planck system of units where Newton's constant is set to 1 is an interesting mathematical curiosity, because in it all the physical quantities become dimensionless.
Nevertheless, when Newton's constant is set to 1, the number of fundamental constants is not reduced, but another constant that was 1 in other systems of natural units becomes a fundamental constant that must be measured experimentally, for instance the elementary charge.
Besides not having any advantage, because the number of fundamental constants in non-nuclear physics remains 2, the system where Newton's constant is set to 1 cannot be used in practice.
The reason is that the experimental measurement of Newton's constant has huge uncertainties. If its value is forced to be the exact "1", then those uncertainties are transferred to the absolute values of all other physical quantities. In such a system of units the only values that would be known precisely would be the ratios of two quantities of the same kind, e.g. the ratios of 2 lengths or of 2 masses. Any absolute value, such as the value of a length or the value of a mass, would be affected by huge uncertainties.
So the use of such a system of units is completely impossible, even if it is mentioned from time to time by naive people who know nothing about metrology. The choice of units for the physical quantities cannot be completely arbitrary, only units that ensure very low uncertainties for the experimental measurements are eligible.
Currently and in the foreseeable future, that means that one of the units that are chosen must be a frequency. For now that is the frequency corresponding to a transition in the spectrum of the cesium atom, which is likely to be changed in a few years to a frequency in the visible range or perhaps in the ultraviolet range. In a more distant future it might be changed to a frequency in a nuclear spectrum, like this frequency that has just been measured for Th229, if it would become possible to make better nuclear clocks than the current optical atomic clocks, which use either trapped ions or lattices of neutral atoms.
Some of the parameters of the "standard model" are fundamental constants associated to the strong and weak interactions. It is debatable whether it makes sense to call as fundamental constants the rest of the parameters, which are specific properties of certain objects, i.e. leptons and quarks.