[00:00] Strange things are happening in physics. It seems&nbsp; that physicists can't agree what's up with the&nbsp;&nbsp; expansion of the universe. Last year, a group&nbsp; claimed that the expansion of the universe does&nbsp;&nbsp; not, as we thought, speed up. That would mean that&nbsp; the 2011 Nobel Prize in physics was awarded in&nbsp;&nbsp;
[00:18] error. The Nobel Prize winners have now pushed&nbsp; back, but their rebuttal was also rebutted,&nbsp;&nbsp; and it's somewhat of a mess really. But here's&nbsp; the brief summary. The universe is currently&nbsp;&nbsp;
[00:30] expanding. This part everyone agrees on. It&nbsp; expands simply because it contains matter and&nbsp;&nbsp; energy. However, in the 1990s, observations&nbsp; of supernovae seem to show something more.&nbsp;&nbsp; The universe doesn't just expand. The expansion is&nbsp; getting faster. Normal matter and energy does not&nbsp;&nbsp;
[00:46] do it. This why physicists had to introduce energy&nbsp; with negative pressure which is called dark energy&nbsp;&nbsp; and not small amounts of it. 2/3 of the energy&nbsp; in the universe would have to be dark energy to&nbsp;&nbsp;
[00:58] fit the observations. The physicists who made the&nbsp; discovery were awarded a Nobel Prize in physics&nbsp;&nbsp; in 2011. This Nobel Prize has been controversial&nbsp; for several reasons. One reason is that at the&nbsp;&nbsp;
[01:10] time many thought it was awarded prematurely. The&nbsp; evidence was not particularly strong back then.&nbsp;&nbsp; And that's true. But then again, the statistical&nbsp; significance has much improved since then and the&nbsp;&nbsp; results seems to have held up. Or maybe it's&nbsp; just confirmation bias. Another reason is that&nbsp;&nbsp;
[01:27] the results partly looked convincing because&nbsp; the discovery was made by two different groups.&nbsp;&nbsp; However, if you do as much as read the author&nbsp; lists or the acknowledgements of the papers, it's&nbsp;&nbsp;
[01:40] obvious that the two groups were in contact with&nbsp; each other and shared results. These were clearly&nbsp;&nbsp; not independent analyses. This doesn't mean the&nbsp; results are wrong, but it's a way that biases can&nbsp;&nbsp;
[01:53] enter. Then last year, a completely different&nbsp; group looked at the supernovi data again, and&nbsp;&nbsp; they said there's a serious systematic mistake in&nbsp; both of the data analyses. You see, the way that&nbsp;&nbsp;
[02:06] one usually infers the accelerated expansion is&nbsp; to look at how supernovae look different depending&nbsp;&nbsp; on how far away they are. And since light moves&nbsp; well with the speed of light, the more distant the&nbsp;&nbsp;
[02:19] supernovi, the further back in time they happened.&nbsp; Looking at supernovae at different distances then&nbsp;&nbsp; tells you how the expansion of the universe&nbsp; has changed. The paper from last year then&nbsp;&nbsp;
[02:32] said actually the different appearances of the&nbsp; supernovae have nothing to do with the accelerated&nbsp;&nbsp; expansion. It's just that the further away the&nbsp; supernovae are the younger the galaxies where the&nbsp;&nbsp;
[02:44] supernovi happened on average and the age of the&nbsp; galaxy influences how the supernovae look. They&nbsp;&nbsp; redid the analysis and found that if one properly&nbsp; removes the effect from the age of the galaxy, the&nbsp;&nbsp;
[02:58] expansion of the universe no longer accelerates&nbsp; and dark energies are necessary. Bold, because&nbsp;&nbsp; unnecessary is not a word physicists usually apply&nbsp; to invisible things that explain everything. The&nbsp;&nbsp; news is now that a group which includes two of&nbsp; the original Nobel Prize winners say that the&nbsp;&nbsp;
[03:16] argument fails. They say that the New Dark Energy&nbsp; paper overestimated how much the age of the galaxy&nbsp;&nbsp; affects the supernova and that whatever's left is&nbsp; accounted for by standard corrections. The bottom&nbsp;&nbsp;
[03:29] line is they say the expansion of the universe&nbsp; is still speeding up. The university put out a&nbsp;&nbsp; bombastic press release that was widely picked up.&nbsp; According to the press release, lead author Dr.&nbsp;&nbsp;
[03:41] Phil Wiseman said, "The previous and well-accepted&nbsp; measurements were in fact fine and our current&nbsp;&nbsp; understanding of the page of the universe remains&nbsp; robust. Thankfully, we have averted this crisis,&nbsp;&nbsp; but the mystery about why the universe is still&nbsp; accelerating in size remains." A press release&nbsp;&nbsp;
[03:58] does not mention that this rebuttal was rebutted&nbsp; already in March by the authors of the original&nbsp;&nbsp; paper who well defend their own analysis. At&nbsp; the same time, another paper was published by&nbsp;&nbsp;
[04:10] a third group which redid the analysis using a&nbsp; different data set of supernovae and found again&nbsp;&nbsp; that the acceleration is not there. This did not&nbsp; get a press release because that would have made&nbsp;&nbsp;
[04:24] the Nobel Prize winners very unhappy. This isn't a&nbsp; joke. It's almost certainly what happened. There's&nbsp;&nbsp; a lot of infighting in departments about whose&nbsp; research will be publicly mentioned and scientists&nbsp;&nbsp;
[04:38] who question the status quo are usually on the&nbsp; losing end. What are we to make of this? These&nbsp;&nbsp; aren't calculations you can check with a pen on a&nbsp; paper. So I can't tell you whose analysis is wrong&nbsp;&nbsp;
[04:50] or right. But I want to offer a general comment&nbsp; about the existence of this discussion. Obviously,&nbsp;&nbsp; the result depends on what you assume happens in&nbsp; the environment of the supernovae and how that&nbsp;&nbsp; enters the observations. This in return depends&nbsp; on how you think galaxies form and develop,&nbsp;&nbsp;
[05:07] which in return depends on our model for the&nbsp; universe. We know that these galaxy formation&nbsp;&nbsp; models are difficult to get right. They have loads&nbsp; of parameters to twiddle that'll give you whatever&nbsp;&nbsp; you want. And still, they somehow managed to screw&nbsp; up the predictions for the earliest galaxies. My&nbsp;&nbsp;
[05:25] takeaway here is therefore that the data is&nbsp; simply insufficient to make a strong case one&nbsp;&nbsp; way or another. Galactic environments are not well&nbsp; understood enough. Not today, and they certainly&nbsp;&nbsp; were not in the 1990s. So those papers all get a&nbsp; five out of 10 on my [&nbsp;__&nbsp;] meter. But thankfully,&nbsp;&nbsp;
[05:44] the crisis was averted by the people whose Nobel&nbsp; Prize depended on averting it. Always reassuring&nbsp;&nbsp; when the universe checks with the committee first.&nbsp; I'm always looking for new product recommendations&nbsp;&nbsp;
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