Did the universe inflate?

Most physicists currently believe that our universe expanded exponentially right after the big bang. This rapid phase of expansion is called "inflation". Its advocates argue that the theory of inflation has made correct predictions. Its critics say that inflation isn't even science. Who is right? They're both right and they're both wrong. In this video I lay out the argument for you.

0:00 Intro
0:53 The controversy
2:09 Did inflation make predictions?
5:47 Does inflation work like the standard model?
8:58 The argument from popularity
9:57 What does inflation explain?
11:34 Who is right now?
12:18 Sponsor message

[trimeris]

Sabine, your ability to present both sides of the argument and bring clarity to each side with such objectivity can be summed up in one word...BRILLIANT!

[gallendugall]

I sympathize with the Universe. I did the same thing when I was feeling isolated and alone. Of course it is harder to get out of the house when houses are just another part of you.

[phillipbox]

I appreciate your pointing out how unfortunate consensus is to science and how social media and politics affect so many subjects. History is replete with such thinking. It’s refreshing to hear a scientist admit we don’t know the absolute truth on so many major areas of study in physics and cosmology. It’s ok to admit we don’t know for sure but the quest requires open mindedness. Learning a previously held tenet is wrong my be hard on egos but is good for science. Just my humble opinion

[petebyrdie]

That was a rollercoaster. Until quarter of an hour ago, I'd thought inflation was pretty much a done deal, as far as scientists were concerned at least.

[wernerhuysegoms]

That makes me think of Einstein's retort (yes, that guy again) when hearing about a book or newspaper article '100 Authors against Einstein', rejecting his theory of relativity: 'If I were wrong, one would be enough'. The number of articles written about a theory can never be an indication of its validity.

[whycantiremainanonymous]

3:20: There is one important difference between predictions and retrodictions, though. It's relatively easy to create a mathematical model (not quite a theory, I admit) that closely fits known data while failing miserably with unknown data points. I've seen this referred to, by statisticians, as "overfitting". You set parameters so they fit the known data closely, but that doesn't mean new information would fit the same mold.

[rotatingmind]

Great to have a view on current cosmology from a higher distance to see the bigger picture. Thank you Sabine.

[TranscendentBen]

9:51 "It's because of arguments like this that people don't trust scientists." I disagree. Very few people who don't trust scientists can follow any such arguments or even give a rough approximation to what science is, much less tell you what cosmology is. They read something about basic established science and see that it disagrees with what they've decided is true and learned from something other than science, and from that they decide science and scientists are wrong.

[TheSkystrider]

I've enjoyed Sabine for a while now but I didn't realize she has the strength to publically challenge big name scientists and outright call them out for wrongness and logical fallacies. I'm proud to be in this community!

[jedgrahek]

I very strongly agree with the perspective of Penrose on this matter. The leap from Hubble's observational data to such grandiose and fantastical conclusions as Inflation and talking about the "singularity of the Big Bang" as though anyone has any actual clue about the truth of any of that, merely that extrapolations based on current observational data using our best models lead to a "singularity", which is just a mathematical paradox. There's a vast gulf between saying "there's a mathematical singularity" and saying "everything began at a single condensed point that then exploded outward in a completely unique, almost miraculous event, which funnily enough coincides very well with vague notions of a monotheistic "creator" performing an "act of creation", but we won't say that out loud ever or reflect on why such a theory might be so inherently attractive for non-scientific reasons". Just like there's a vast gulf between "we've hit a wall in our ability to measure reality, so we are forced to use compromises and probability schemes to do the math" and "nothing is real, fundamentally at the most basic level things exist in superposition, which Schroedinger made up this great analogy for to make the concept make more sense (when he literally made up the cat thought experiment to directly show people how absurd the concept of superposition was if taken literally and not seen as simply a mathematical tool), and what this means is that at every instant, because of the infinite possibilities always present due to everything being in superposition and nothing being real, infinite parallel universes are created and splinter off for every possible different outcome of superposition. I am a serious physicist. Einstein's thinking was so limited, hahaha."

[FrederickStadler]

Dear Sabine, I watch all your videos and I'm a really big fan. I feel, whether certain opinions are correct or not, they are always worth listening to. Thank you for your hard work on the sciences.

[franksydnor]

I just love the way Sabine cuts to the chase and gets right to the core of the problem. So refreshing to see complex points and counter-points eruditely stripped down to their bare forms.

[jaylewis]

This is such a concise explanation of how to think and how even many experts fall into cognitive traps

[CAThompson]

The best videos are the ones that at least keep me entertained and I'll learn something anyway, even if half of it goes over my head (again.)
I can now put 'cosmic inflation' firmly on the pile of cosmology and physics things that aren't actually sorted, and if it ever comes up in conversation I can 'well, actually...' with confidence.
Thank you, Sabine! :)

[yuvalne]

Possibly my favourite Sabine videos are the ones in which the smacks some proper science onto other scientists. Keeping science in check like that is extremely important, and I am so glad Sabine takes part in that.

[someguy-kh]

I have looked at the inflationary model as special pleading ever since I first heard it. Of course it makes a prediction, it was specially tweaked to do just that. That is why predictive ability is a necessary but not sufficient condition for accepting a hypothesis.
There are many good explanations for why we would see inflation in an early universe, but none of them tell us why it stopped or why it lasted for the precise amount of time we would like. These gaps point out the synthetic nature of the theory's origin.

[cosmosandchill]

Damn, I didn't realise that Inflation was on such shaky ground. Thought it was a "done deal" scientifically-speaking. It's also bizarre to see people like Alan Guth use such rookie logical fallacies to support a theory that should speak for itself. Would love to see a video on alternatives, especially cyclic cosmologies!

[curiousuranus]

Another corking episode, Sabine - I particularly like the 'Let's discuss the rules of football, rather than playing the game' argument

[enterprisesoftwarearchitect]

Although I just watched Alan Guth teach an MIT course on inflation, Penrose doesn’t agree that it would make the universe isotropic. Guth says inflation predicts Omega will be 1 as Sabine points out.

[ninadesianti]

Thank you for reminding us the importance of scientific method. And you brilliantly incorporated the ads into the video, what a smooth transition. I always enjoy your videos! Thank you for making them!