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Evidence that the key assumption made in discovery of dark energy is in error

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Re: Evidence that the key assumption made in discovery of dark energy is in error

#121

If you find things like this interesting I suggest you look on youtube for videos on the electric universe. The main take is that our current models having gravity as the main driving force shaping our universe is a misunderstanding - hence rejecting the idea of dark matter / dark energy that was "invented" to make for math for gravity work with the observations of expansion.

Despite the similar name, dark matter really has very little to do with dark energy, and the lines of evidence for them are totally different. AFAIK there is fairly overwhelming evidence for the existence of dark matter at this point, and it's mostly a question of what exactly it is rather than whether the effect is real.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#122

Earlier quoted context omitted.

If I am reading this correctly, in plain English what it seems like they are suggesting is that old Type Ia supernovae worked differently from newer supernovae; e.g. that a Type Ia supernova 5 billion years ago had a different brightness curve than a Type Ia supernova from 50 million years ago. On its face this seems like an extraordinary claim; I can’t think of how to square it with the (fundamental) assumption that…

Do the current models of dark energy not have it changing over time? Or at least allow for the possibility? The idea that fundamentally, physical law does not change over time, is either a metaphysical or methodological assumption (or a bit of both), but it is certainly not an empirically-derived result, and it clearly does not rule out manifestations of those fundamental laws changing over time.

The issue is much more prosaic than the fundamental laws of physics changing over time. On average, very distant supernovae have a different composition than nearby supernovae. As the universe ages, more light element atoms are fused into heavier element atoms and expelled into space. That material is incorporated into the next generation of stars, so stars begin their lives with less and less hydrogen, as the universe ages. If that influences the light curves of supernovae, then it greatly complicates the use of supernovae as standard candles for distance measurement.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#123

If you find things like this interesting I suggest you look on youtube for videos on the electric universe. The main take is that our current models having gravity as the main driving force shaping our universe is a misunderstanding - hence rejecting the idea of dark matter / dark energy that was "invented" to make for math for gravity work with the observations of expansion.

... you mean this?

https://www.vice.com/en_us/article/nz7neg/electric-universe-...

Re: Evidence that the key assumption made in discovery of dark energy is in error

#124

If you find things like this interesting I suggest you look on youtube for videos on the electric universe. The main take is that our current models having gravity as the main driving force shaping our universe is a misunderstanding - hence rejecting the idea of dark matter / dark energy that was "invented" to make for math for gravity work with the observations of expansion.

It should be noted that among cosmologists, electric universe is widely considered to be bunk science.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#125
It is hard to overstate how important the resolution of this question is to physics, and in particular to theoretical physics. The “cosmological constant problem”, that is the problem explaining the cosmological acceleration (if it exists), is arguably the most important and hardest question in high energy theoretical physics. Many theoreticians have spent significant effort studying this question, working under the assumption that the empirical evidence is solid. If this is not the case, it changes the landscape of cutting edge physics research.

There are several reasons why explaining the observed acceleration is so hard. The cosmological constant (the measure of how much dark energy there is) is a tiny positive number which seems to require a lot of “fine tuning” to explain theoretically. We can easily include it in general relativity, but our best understanding of quantum physics says that if it is there then it should be much larger. This means there probably is something we don’t understand about its microscopic origins. If we try to build a microscopic model that has this small constant using string theory (our best guest at a complete theory), we find that such models are hard to create. In fact, it is not clear that any model that includes dark energy is even valid in string theory! Any way we look at it, it seems more difficult to explain this number if it is tiny and positive than if it is strictly zero (no acceleration).

Finally, theoreticians don’t have much to go on when explaining this phenomenon besides this one single number — there aren’t closely related experiments we can combine to come up with a coherent picture of what’s happening. Combine this with particle physics, where accelerators provide us with an abundance of data. It is a single tiny number that has puzzled theoreticians for decades.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#126

Earlier quoted context omitted.

> However, if you were to change our relativistic reference frame to match a distance galaxy's As a causal science enthusiast I am lost, how does one change our relativistic reference frame?

Consider yourself. Consider a galaxy N million lightyears away that is moving away from you at high speed... Or is it really? What if it's staying perfectly still, and YOU'RE the one moving? ... How could you even tell? The principle of Relativity is that you cannot tell any difference, for the laws of physics are the same whether you are moving or the galaxy is moving. The theory of Special Relativity describes whic…

... at which point you also get to enjoy your arrival at linguistic metaphysics. If you can identify all material objects that all observers can feasibly see, then you subtract the material objects that one person sees, from the material objects the other person sees in their reference frame, and you end up with... something... that is both a material object, and not a material object at the exact same point in time. So, does that material object actually exist? If so, in what way does that material object exists for the person who cannot feasibly perceive a feasibly perceivable object in any capacity? Kind of like theseus's ship launched into the space-time continuum?

Re: Evidence that the key assumption made in discovery of dark energy is in error

#127

To know if the universe is expanding, we need to know the following: how far away things are, and whether they're moving away from us. In an accelerating universe, there's evidence that things were moving away from us slower in the past. The evidence that things are moving away from us is that as the universe expands, the wavelength of any light travelling through it also expands, shifting it towards the red end of t…

Speaking from the pov as a former astrophysicist, that definition of redshift is not quite accurate. While we have observed the universe expanding since Edwin Hubble published his findings 90 years ago, it was in fact the Friedmann equations produced 10 years earlier that established how it would work within the context of general relativity. The Universe is expanding at every known point at the same time at the same…

> The Universe is expanding at every known point at the same time at the same rate

No, it's not. The (local) metrics sourced by the Earth, Earth-Moon, Sun, solar system, Milky Way, and the Local Group are not at all like FLRW with or without a cosmological constant, while all those metrics are very much like Kerr or LTB, wherein ordinary matter like gas and dust gradually condenses into a point. Conversely, the metric globally is very much like FLRW with a small positive cosmological constant, and very much unlike a spacetime in which matter condenses into a point.

We can use Israel junctions to knit together "stacks" of regions that are well-approximated by a Kerr or LTB metric, and ultimately knit galaxy cluster sized LTB regions into expanding FLRW, representing the LTB regions as dust particles. This matches observations very well, and is called a "swiss cheese" cosmology, the name arising from how gravitational collapse ultimately creates voids -- holes -- in the otherwise homogeneous diluting dusts.

Kolb and others have a decent overview of how an Einstein-de Sitter-Lemaître-Tolman-Bondi swiss cheese universe works (the paper is in the context of the homogeneous-vs-inhomogeneous+backreacting cosmology debate, which is largely about connecting theory with astrophysical observations of a somewhat lumpy real universe especially in the transition from the matter-dominated era to the dark-energy dominated era) : https://www.osti.gov/biblio/21023997-cosmological-observable... ( PDF https://archive-ouverte.unige.ch/files/downloads/0/0/0/3/6/5... ). There's a good textbook treatment in Harwit's _Astrophysical Concepts_ as well (a preview exists at https://books.google.co.uk/books?id=gZfuBwAAQBAJ&pg=PA516&lp... ), and MTW has a (not very easy) overview of Israel-Darmois junctions in §21.13.

Such swiss cheese models match observations so well that it would be surprising (in a cool way) to find that there is any metric expansion at all in our solar system or in any of the galaxies and galaxy clusters we observe on the sky. We don't see that, though. In particular, one should take into account the evidence for accelerated expansion over the past few decades. Given that, one can consider a "fifth-force" (or nth, given Higgs etc.) representable as a field with a density and gradient, rather than the purely geometrical scaling in \Lambda-CDM. (This is at the root of some quintessence projects.) Results usually involve a lot of dynamics to suppress cosmological shear and other "little rip" effects at the margins of clusters with highly-luminous components, and adding several degrees of freedom that lack other physical support seems a lot worse than accepting an Einstein-de Sitter like swiss cheese geometrical model.

> local reference frame

It has nothing to do with reference frames; the metric tensor focuses matter and light one way or another (cf. Raychaudhuri) and within galaxy clusters practically all matter is focused towards a point in the future, whereas globally the same matter, and all other matter, and light, focus towards a point in the past (and the future focus points within galaxy clusters do not themselves focus together in the future). The only requirement is that the manifold is Lorentzian and time-orientable; you can use any system of coordinates that an arbitrary observer carries around with it, and you only need to do that if you care to describe when in the past or future and/or where relative to an observer the focus points lie.

> ... to match a distant galaxy's ...

How do you propose to do that? I think it's worth it for you to think about that a little: does your conception of a frame in which \lambda_{obsv} = \lambda_{emit} (rather than 1 + z = \frac{\lambda_{obsv}}{\lambda_{emit}}) extend into the distant past and distant future? How accelerated is this z-suppressing frame? In this frame what's the expectation for the wavelength of a CMB photon over time, or for galactic and extragalctic H I lines ?

> doppler expansion due to the nature of differing relativistic reference frames

Kinematical interpretations fall apart really spectacularly at high z, and conveniently we have a probe of (6 > z > 1) in the https://en.wikipedia.org/wiki/Lyman-alpha_forest which is a challenge for constructing a sensible z-suppressing frame of reference.

(See also MTW §29.2)

Re: Evidence that the key assumption made in discovery of dark energy is in error

#128
post #38

Earlier quoted context omitted.

> Dark energy is something predicted by general relativity Not really. GR can accommodate it just fine, but GR did not predict it. In fact, Einstein, who originally introduced the cosmological constant (which was the term then for what we now call "dark energy") in order to allow a static solution to his equation, thereby missed the chance to predict that the universe was expanding, a decade before Hubble's observati…

How much would the fate of the universe page on Wikipedia change with linear expansion? Do we have a bit longer before the stretch?

I'm not sure what you mean by "linear expansion". If you mean that the rate of change of the scale factor with respect to time never changes at all, that is not possible except in the edge case of a universe containing zero matter or energy and zero cosmological constant. (This edge case is often called the Milne universe.) Which is obviously not the universe we live in.

If you just mean "no dark energy", i.e., the model that most cosmologists used before the 1990s when accelerating expansion was discovered, it wouldn't change the universe's long term fate very much. It would still expand forever and become more and more diluted; the expansion would just slow down forever instead of accelerating forever. There would be some differences as far as our observable universe--we would not eventually become isolated from all other galaxies and unable to see them--but that's about all.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#129
post #114
post #108

Earlier quoted context omitted.

Your ruler is absolute distances, like the speed of light. You can inflate or deflate the balloon and the number of marks on its surface won't change. But the time required for the light to travel between them will.

Stupid question - How do you know for certain it isn’t just that light is slowing down? Relativity probably doesn’t work this way at all, but if light did actually slow down, would it be perceived by us as light moving at the same speed across a greater distance?

I asked Ann Nelson (look her up) this when I audited her cosmology class in grad school, thinking I'd come up with a great new idea. She said yes, it's equivalent to the speed of light changing, and then moved on.

Re: Evidence that the key assumption made in discovery of dark energy is in error

#130
post #114
post #108

Earlier quoted context omitted.

Your ruler is absolute distances, like the speed of light. You can inflate or deflate the balloon and the number of marks on its surface won't change. But the time required for the light to travel between them will.

Stupid question - How do you know for certain it isn’t just that light is slowing down? Relativity probably doesn’t work this way at all, but if light did actually slow down, would it be perceived by us as light moving at the same speed across a greater distance?

Bear in mind that time is not universal. For the speed of light to change over time, it would change at different rates for observers in different reference frames, and this difference would be measurable.

As to the previous question about relative size. If the universe doubled in size, the objects within it such as atoms don’t also double in size. Gravity and the atomic forces don’t change, so eg the size of stable electron orbits or planetary orbits don’t double in size.

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