<p>This question strikes at the foundations of modern cosmology, and I must stress that I am not 100% confident in the following answer.</p>
<p>The point is that when we, e.g., point a telescope at a supernova, we don't immediately get a &quot;distance to the supernova&quot; (remember supernovae is the cause of half of the Hubble tension). What we get is an <em>apparent magnitude</em>. This is compared to the <em>absolute magnitude</em>, which is then converted into a <em><a href="https://en.wikipedia.org/wiki/Luminosity_distance" rel="nofollow noreferrer">luminosity distance</a></em>. From there, we convert to the cosmologically-relevant <em>comoving distance</em> by applying a cosmological model. Therefore, once you swap cosmological models, your distance-to-the-supernova changes, and the Hubble tension can conceivably disappear.</p>
<p>What does MOND have to do with it? As you surely know, the current standard cosmological model is <span class="math-container">$\Lambda$</span>CDM. This particular model assumes that the universe is homogeneous, isotropic, and governed by General Relativity (which, combined, lead to the Friedmann Equations). If you shake any of these three assumptions, then you no longer have <span class="math-container">$\Lambda$</span>CDM; once you no longer have <span class="math-container">$\Lambda$</span>CDM, because your conversion to comoving distance is different, the Hubble tension might disappear too. This is why people are also investigating whether anisotropic models can resolve the Hubble tension (<a href="https://arxiv.org/abs/2201.04548" rel="nofollow noreferrer">example</a>).</p>
<p>As you point out, MOND was conceived as an explanation for galaxy rotation curves without invoking dark matter, which <em>a priori</em> does not have any relation to the Hubble tension. However, you should go further: if MOND turns out to be correct, then it would modify General Relativity, and everything built on GR might no longer hold. Because <span class="math-container">$\Lambda$</span>CDM (and most of modern cosmology) includes GR as a framework assumption, this means <em>nearly everything</em> we currently believe to be true in cosmology might no longer hold. For example, MOND might also remove the need for dark energy. This would need to be proved theoretically, of course, but it can conceivably happen.</p>
<p>If you're interested in how our understand of cosmology depends on the model, check out <a href="https://arxiv.org/abs/1103.5331" rel="nofollow noreferrer">this 2011 paper by Ruth Durrer</a>.</p>

CC BY-SA 4.0
2024-06-25T09:19:49.260Z
2024-06-25T09:19:49.260Z
Allure
<p>So basically, I have to make this presentation about the hubble tension, but I discovered that new hypothetical solutions have been found, like the MoND model or better calibrations for the cepheids distance calibrations.</p>
<p>The thing is, I don't quite understand how a model that wished to solve the dark matter problem through the study of galaxies could probably solve the hubble tension, which is here on a intergalactical level.</p>
<p>I know that the MoND has a lot of problems on his own, like incompatibility with special relativity and the fact it's not a field theory, but I just don't get this link between hubble tension and dark matter.</p>
<p>I'd like to highlight that if you'd have other model examples, it could help me a lot, but it's the main one I've heard of apart our current λcdm model.</p>
<p>Im also kind of new to this, so if you'd have some recommendations on the subject I'd be more than happy to take a look!</p>

<expansion><dark-matter><hubble-constant>
How could a new cosmological model solve the hubble tension?
Anais-Ellie Gucek
# How could a new cosmological model solve the hubble tension?

(Asked by: username_0 on 2024-06-23)

So basically, I have to make this presentation about the hubble tension, but I discovered that new hypothetical solutions have been found, like the MoND model or better calibrations for the cepheids distance calibrations.

The thing is, I don't quite understand how a model that wished to solve the dark matter problem through the study of galaxies could probably solve the hubble tension, which is here on a intergalactical level.

I know that the MoND has a lot of problems on his own, like incompatibility with special relativity and the fact it's not a field theory, but I just don't get this link between hubble tension and dark matter.

I'd like to highlight that if you'd have other model examples, it could help me a lot, but it's the main one I've heard of apart our current λcdm model.

Im also kind of new to this, so if you'd have some recommendations on the subject I'd be more than happy to take a look!

**Tags:** expansion, dark-matter, hubble-constant

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## 1 answers

### Answer by username_1 on 2024-06-25. Score: 2 | Accepted answer

This question strikes at the foundations of modern cosmology, and I must stress that I am not 100% confident in the following answer.

The point is that when we, e.g., point a telescope at a supernova, we don't immediately get a "distance to the supernova" (remember supernovae is the cause of half of the Hubble tension). What we get is an *apparent magnitude*. This is compared to the *absolute magnitude*, which is then converted into a *[luminosity distance](https://en.wikipedia.org/wiki/Luminosity_distance)*. From there, we convert to the cosmologically-relevant *comoving distance* by applying a cosmological model. Therefore, once you swap cosmological models, your distance-to-the-supernova changes, and the Hubble tension can conceivably disappear.

What does MOND have to do with it? As you surely know, the current standard cosmological model is $\Lambda$CDM. This particular model assumes that the universe is homogeneous, isotropic, and governed by General Relativity (which, combined, lead to the Friedmann Equations). If you shake any of these three assumptions, then you no longer have $\Lambda$CDM; once you no longer have $\Lambda$CDM, because your conversion to comoving distance is different, the Hubble tension might disappear too. This is why people are also investigating whether anisotropic models can resolve the Hubble tension ([example](https://arxiv.org/abs/2201.04548)).

As you point out, MOND was conceived as an explanation for galaxy rotation curves without invoking dark matter, which *a priori* does not have any relation to the Hubble tension. However, you should go further: if MOND turns out to be correct, then it would modify General Relativity, and everything built on GR might no longer hold. Because $\Lambda$CDM (and most of modern cosmology) includes GR as a framework assumption, this means *nearly everything* we currently believe to be true in cosmology might no longer hold. For example, MOND might also remove the need for dark energy. This would need to be proved theoretically, of course, but it can conceivably happen.

If you're interested in how our understand of cosmology depends on the model, check out [this 2011 paper by Ruth Durrer](https://arxiv.org/abs/1103.5331).


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