In cosmology, the Hubble constant is constantly debated… but what is it and why does it matter?
In general, it’s an incredibly important number because it determines so much of what
we know about the universe - including its age, history, and future. And yet,
it’s a figure that’s also troublesome and mysterious. It’s hard to get an
exact value for it… and it’s at the crux of one of science’s toughest problems.
Now, though, we might’ve made a breakthrough with it, and it takes us into a phantom mirror world.
This is Unveiled and today we’re answering the extraordinary question;
Did scientists just uncover the secret mirror universe that holds reality together?
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We start almost one hundred years ago. In the early twentieth century, when astronomers began
working with all-new technology, the basic concept of even multiple galaxies was still way off.
To most minds back then, our galaxy – the Milky Way - was also the entire universe,
containing every single star, planet, and object. In the 1920s, however, the astronomer Edwin Hubble
thought that there was probably something more (something else) to the bizarre, faint object
he was then looking at through his telescope. At the time, that object was generally thought to be
nothing more than a nebula… but Hubble suggested that it looked more like an “island universe”.
And, as it turns out, it was the Andromeda galaxy, the first galaxy ever found outside of our own.
Over time, Hubble would go on to find and measure more galaxies,
steadily building his legacy as one of the most influential astronomers of all time.
Along the way, though, he discovered something further… that again shocked scientists around
the world. Not only were there many other galaxies in the universe besides our own,
but they were also moving away from us. And the farther away they were, the faster they
were retreating. Of course, we now understand that this is because the universe is expanding.
While the rate of that expansion is what’s come to be known as the Hubble constant.
From there, though, it’s not exactly straightforward. Hubble’s initial measure of his
constant worked out as 501 kilometers per second per megaparsec. But ultimately, this figure also
stands as the first example of just how difficult it is to measure the constant with accuracy…
because Hubble, it seems, was way off, with his number being at least ten times higher than most
modern estimations. It gets still more confusing, though, because despite the name… it turns out the
number isn’t actually a constant, at all. Thanks to laws set out by what are known as the Friedmann
equations, we know that the rate of expansion of the universe simply can’t stay the same. That it
all depends on the density of matter and energy in the universe, which all changes with expansion.
It’s some heavy math, but it essentially means that the Hubble constant (the expansion rate of
the universe) is always updating and fixing itself. It never actually stands still.
And then there’s yet one final, major sticking point in the story of the Hubble constant; the
Hubble tension. This refers to how the constant (a number that’s ever-changing anyway) also changes
depending on how it’s measured. There are a variety of methods used, but they don’t all arrive
at the same number. They generally fall somewhere between 65 and 75 kilometers per second per
megaparsec. Again, it’s a range that’s comfortably lower than Hubble’s initial calculation,
but there is (at present) no single, agreed upon value. This discrepancy (this tension) is not
then easily resolved. No one seems to know why the numbers don’t match up, and that’s a big problem
if ever we’re trying to show how the universe really works. But that could be about to change.
A contemporary, multi-authored study, published in May 2022 in the journal “Physical Review Letters”,
aims to resolve the Hubble tension once and for all by predicting the existence
of a mirror world that exists alongside our own. This mirror world (if it is there) is an
exact copy of ours but is invisible, and the only interactions it has with us are through gravity.
In the proposed world, every particle that exists in our world may have a mirror opposite… and it’s
as though there’s a point of overlap between here and there, which could serve to settle
the Hubble tension and therefore finally explain why our universe is like it is.
In a statement, those behind the study explain that their research involves applying scaling
symmetry to the universe. They note that; “a lot of the observations we do in cosmology have an
inherent symmetry”… so there is precedent for this approach. However, in this case,
for the scaled symmetry to stick (and keep sticking) it was found that there had to be
another, separate, mirror dimension out there somewhere, beyond our own,
but still exerting a gravitational force upon our universe. As to what that mirror
dimension could be made of, the leading theory says dark matter. Dark matter has before been
used to explain seemingly “missing mass” in our universe; an unknown something that apparently has
an impact on our gravity… and so, this could be the latest extension of that. Which is exciting,
because it potentially means that the mirror model could actually solve two of the biggest problems
in cosmology, if it’s correct - the Hubble tension and the true nature of dark matter.
What’s perhaps a little surprising, then, is that the general idea of a mirror world (or
phantom plane) isn’t actually new. It can, in general, be traced back to at least the 1990s,
but it’s only now been applied for the first time to also solve the Hubble tension. Similarly,
research in 2018 theorized the existence of a mirror world, as well… although instead
of it being one that dealt with gravity, it was instead built around the function of time. Here,
it was suggested that a mirror universe might’ve existed before the Big Bang, from which point it
moved backwards in time, perfectly reflecting our own experience of time moving forward.
This model and the more recent mirror theory are not related, but they perhaps do share
some similarities in terms of how they make us feel in the here-and-now. Because, in whatever
form it takes, if there is a mirror world out there then, naturally, the next questions are;
what’s it like there? And could we ever break into it? Without effectively turning ourselves inside
out (either physically or temporally) it seems unlikely that we, ourselves, would ever be able to
travel through such a place… but there have been various predictions made as to how a mirror world
might work. If there are reflected copies of every known particle there, for example,
from our perspective, then it could be that it’s a realm that’s extremely similar to our own.
We might think of the elements, objects and life forms that live there, though, as “dark” versions
of what we know. In science fiction, this idea is often used to imply an evil or volatile state…
but, really, the “darkness” is more a reference to the fact that everything on the other side
can’t be seen. It’s hidden, secret, and ultra-mysterious… and, who knows, if all of
that does exist, then might those dark life forms in their dark reality also be thinking about,
predicting, and attempting to study us in return? To them, are we a hidden-but-theorized world,
waiting to be discovered? Are there problems in their own physics, that
only make sense if another world is realized? For now, the implications aren’t yet quite so
fantastic as that. But still, this latest research does offer a promising, potential solution to
the Hubble tension. It’s not the finished article, and there are sure to be follow up
investigations to try and more fully figure out this especially tricky aspect of the universe.
For one, NASA will soon launch the Nancy Grace Roman Space Telescope, which is set to become a
crucial, flagship facility in our quest to better understand the universe’s rate of expansion,
the Hubble constant, the most distant objects away from us, and if, how and where
dark matter comes into the equation. And, as with so many of science’s open questions about space,
we might expect the freshly launched James Webb Space Telescope to contribute some answers, too.
Until we gain an even clearer idea, then, we can spend some time simply pondering the phantom,
reflected world that might be out there… where particles perhaps converge in such a way that
even your very own life experience is played out again, but different.
It might feel a little strange, but it could also be vitally important. Because that’s how
scientists may have just discovered a secret mirror universe that holds reality together.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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