“Observations indicate that the universe is expanding at an ever increasing rate. It will expand forever, getting emptier and darker.” -Stephen Hawking
Today’s Ask Ethan comes to us via our question/suggestion box from reader MIUFish, who asks:
I read something recently about some people who were doing work looking at the possibility that the mass of things has been decreasing, as an alternate explanation – or, perhaps, interpretation – to some of the questions regarding the expansion of the universe and so on.
Is there any seriousness to this? Do you know anything about it?
Here’s what MIUFish is talking about.
For every galaxy we see in the Universe, we can measure how the light coming from it is shifted. Galaxies that appear to be moving towards us have their spectral lines — that is, lines absorbed from or emitted by neutral atoms — shifted. The amount of the shift is in direct proportion to a combination of:
- How quickly the object is moving towards us (for blueshifts) or away from us (for redshifts), in addition to
- How much the spacetime fabric of the Universe has expanded (for redshifts) or contracted (for blueshifts) from the time the light was emitted to the time it arrives at our eyes.
Combine both of those two things, and that accounts for the observed red-(and blue-)shifts of all the galaxies ever observed.
For galaxies that are very far away, the first part — how quickly they move — is negligible compared to the very large expansion of spacetime. That light has been traveling for billions of years, and so by measuring how that light redshifts for galaxies at different distances, we can reconstruct exactly how the Universe has expanded over its history.
At least, that’s how it works if you accept General Relativity as the laws that govern our Universe, and conclude that the Big Bang describes our cosmology based on the evidence.
But that’s not the only possibility, and recently, one proposed alternative has garnered some attention.
You see, instead of an expanding Universe stretching the wavelengths of photons, we could instead tweak the masses of the particles in the Universe, gradually, over time, so that light emitted a long time ago would be redder because the quantum physics underlying atomic transitions was different.
The idea comes from Christof Wetterich (and you can read his paper here), one of the rare people who’s had a speculative idea in the past that was so intriguing I highlighted it for you on this blog. This idea might seem counterintuitive, but it’s really incredibly simple. Think about Newtonian gravity for a minute, if you will.
Imagine you’ve only got two masses in the Universe, they’re getting farther apart, and the only thing you can measure is the force between them.
So what do you see? As r goes up, the force goes down, and it goes down like r -2.
But could you be sure that r was going up, and not that G was (or the two ms were) going down? No, not if the force was the only thing you could measure.
And so it goes with the galaxies in our Universe.
We can measure only a few things about these distant galaxies, and the rest we have to infer. Because our experiences (and experiments) with spacetime and with masses tell us that the mass of particles doesn’t change but spacetime does expand, contract and otherwise curve, we assume that’s how the Universe works on scales where we can’t do experiments.
But Wetterich’s idea could work, too. But here’s what isn’t being reported: it comes at a cost.
You see, in an expanding Universe governed by General Relativity, there’s a very powerful prediction that comes out: the expansion rate of the Universe at all times is determined by a combination of the curvature and energy density of the Universe. All the stuff in the Universe tells us, at all times, how the Universe has expanded, and therefore how objects should be redshifted.
So in our Universe, we observe that galaxies at different distances have different redshifts in a particular manner, and that tells us what the Universe is made out of.
We can then reconstruct exactly what we know to be in the Universe at all times, make predictions as to how the Universe did evolve and will evolve, and test them out.
We can compare these predictions with data sets that come from the Cosmic Microwave Background, the Large Scale Structure in the Universe, and Big Bang Nucleosynthesis, among others. As we’ve gone over, the agreement is astounding.
But if it isn’t the expanding Universe that causes the redshifts, if instead the masses are changing, all of that predictive power disappears.
The fluctuations in the microwave background just happen to be this way because the mass changed in such a way to produce it, not because of the powerful underlying physics. The Universe is speeding up now not because there’s an inherent energy (dark energy) to spacetime, but because the way that mass changes is contrived to produce that effect. And this is true for pretty much every such observation.
But you’d never have gotten this nuance from reading the news that came out about it.
This is the most common type of question I receive, and it goes something like,
Hey, I saw this story that made some outlandish claim. It’s been getting a lot of attention and maybe even some news coverage, but is it true? Can you weigh in.
And every single time, it crushes me a little bit. Because people writing about it are supposed to provide nuance and context when a new find comes out, and to fact-check. You know, to take pride in what you do for a living. And there is some very, very good science writing and science journalism out there. But there’s also this.
Really? Spacetime is just an illusion? No, and no one (reputable) is saying that it is.
What the actual research says is more like, “Hey, have you ever heard of quantum field theory (QFT)? That’s a way — okay, the way — of calculating how the particles and fields in the Universe interact, and how they produce measurable things like cross-sections and scattering amplitudes. But there’s a limit to what you can do with it.”
“Well, there’s a new mathematical technique that may be promising for calculating some of the cross-sections and scattering amplitudes we can’t calculate with QFT. It’s based in geometry, and it’s just mathematics right now (as in, we can’t yet do these calculations for the particles and fields that describe our Universe), but this is potentially very interesting!”
But it gets worse.
Yes, there was a story released this week about some theoretical work that postulates our three-dimensional Universe originated from a higher-dimensional Universe. An idea, by the way, that goes back to at least 1980!
But I assure you, wherever our Universe came from, the Big Bang is still correct, and you’d hope a science writer would know that!
Let me summarize: some incredibly speculative research that did not pass peer review and wound up in the sham-science Journal of Cosmology wound up hitting the front page of many newspapers making an outlandish claim with completely insufficient supporting evidence.
I don’t know why some people have so little integrity when it comes to their own work. Is it churnalism? Is the time it takes to do a decent job too much for the amount you’re paid?
It makes me incredibly sad every time I see a story like this, because I feel that the very people who are supposed to be assisting the public’s understanding of science are behaving in a way that actively undermines it. Where is the fact-checking? Where is the editor to step in and say, “this isn’t newsworthy.” When did it become acceptable to fail to provide the correct context, and instead to just write the most sensationalist headline, accompanied by an article devoid of substance?
It’s yellow journalism, plain-and-simple.
I wish it didn’t exist. I wish it weren’t everywhere. And I wish everyone involved in science communication behaved more ethically, like there was this inherent value in getting the science right. Like it was important to be careful, to get the facts right, to educate people about what’s real, and to do the research to make sure you’re getting it right when you talk about scientific truths.
Those last three articles (except the satire) that I screenshotted for you were all from this week, and this wasn’t really an atypical week. Playing whack-a-mole like this would be a full-time job, and it would be a losing effort.
So although I’ll take the occasional bait when something really raises my hackles, I’ll stick to mostly writing about what we know, what’s real, and telling you how we came to know it. With nuance, and facts, and evidence. Because even if everyone else doesn’t care, I do, and I’m betting you do, too.