Nobel Prize Under Fire: Is Dark Energy Real?

[00:00] Strange things are happening in physics. It seems  that physicists can't agree what's up with the   expansion of the universe. Last year, a group  claimed that the expansion of the universe does   not, as we thought, speed up. That would mean that  the 2011 Nobel Prize in physics was awarded in  

[00:18] error. The Nobel Prize winners have now pushed  back, but their rebuttal was also rebutted,   and it's somewhat of a mess really. But here's  the brief summary. The universe is currently  

[00:30] expanding. This part everyone agrees on. It  expands simply because it contains matter and   energy. However, in the 1990s, observations  of supernovae seem to show something more.   The universe doesn't just expand. The expansion is  getting faster. Normal matter and energy does not  

[00:46] do it. This why physicists had to introduce energy  with negative pressure which is called dark energy   and not small amounts of it. 2/3 of the energy  in the universe would have to be dark energy to  

[00:58] fit the observations. The physicists who made the  discovery were awarded a Nobel Prize in physics   in 2011. This Nobel Prize has been controversial  for several reasons. One reason is that at the  

[01:10] time many thought it was awarded prematurely. The  evidence was not particularly strong back then.   And that's true. But then again, the statistical  significance has much improved since then and the   results seems to have held up. Or maybe it's  just confirmation bias. Another reason is that  

[01:27] the results partly looked convincing because  the discovery was made by two different groups.   However, if you do as much as read the author  lists or the acknowledgements of the papers, it's  

[01:40] obvious that the two groups were in contact with  each other and shared results. These were clearly   not independent analyses. This doesn't mean the  results are wrong, but it's a way that biases can  

[01:53] enter. Then last year, a completely different  group looked at the supernovi data again, and   they said there's a serious systematic mistake in  both of the data analyses. You see, the way that  

[02:06] one usually infers the accelerated expansion is  to look at how supernovae look different depending   on how far away they are. And since light moves  well with the speed of light, the more distant the  

[02:19] supernovi, the further back in time they happened.  Looking at supernovae at different distances then   tells you how the expansion of the universe  has changed. The paper from last year then  

[02:32] said actually the different appearances of the  supernovae have nothing to do with the accelerated   expansion. It's just that the further away the  supernovae are the younger the galaxies where the  

[02:44] supernovi happened on average and the age of the  galaxy influences how the supernovae look. They   redid the analysis and found that if one properly  removes the effect from the age of the galaxy, the  

[02:58] expansion of the universe no longer accelerates  and dark energies are necessary. Bold, because   unnecessary is not a word physicists usually apply  to invisible things that explain everything. The   news is now that a group which includes two of  the original Nobel Prize winners say that the  

[03:16] argument fails. They say that the New Dark Energy  paper overestimated how much the age of the galaxy   affects the supernova and that whatever's left is  accounted for by standard corrections. The bottom  

[03:29] line is they say the expansion of the universe  is still speeding up. The university put out a   bombastic press release that was widely picked up.  According to the press release, lead author Dr.  

[03:41] Phil Wiseman said, "The previous and well-accepted  measurements were in fact fine and our current   understanding of the page of the universe remains  robust. Thankfully, we have averted this crisis,   but the mystery about why the universe is still  accelerating in size remains." A press release  

[03:58] does not mention that this rebuttal was rebutted  already in March by the authors of the original   paper who well defend their own analysis. At  the same time, another paper was published by  

[04:10] a third group which redid the analysis using a  different data set of supernovae and found again   that the acceleration is not there. This did not  get a press release because that would have made  

[04:24] the Nobel Prize winners very unhappy. This isn't a  joke. It's almost certainly what happened. There's   a lot of infighting in departments about whose  research will be publicly mentioned and scientists  

[04:38] who question the status quo are usually on the  losing end. What are we to make of this? These   aren't calculations you can check with a pen on a  paper. So I can't tell you whose analysis is wrong  

[04:50] or right. But I want to offer a general comment  about the existence of this discussion. Obviously,   the result depends on what you assume happens in  the environment of the supernovae and how that   enters the observations. This in return depends  on how you think galaxies form and develop,  

[05:07] which in return depends on our model for the  universe. We know that these galaxy formation   models are difficult to get right. They have loads  of parameters to twiddle that'll give you whatever   you want. And still, they somehow managed to screw  up the predictions for the earliest galaxies. My  

[05:25] takeaway here is therefore that the data is  simply insufficient to make a strong case one   way or another. Galactic environments are not well  understood enough. Not today, and they certainly   were not in the 1990s. So those papers all get a  five out of 10 on my [ __ ] meter. But thankfully,  

[05:44] the crisis was averted by the people whose Nobel  Prize depended on averting it. Always reassuring   when the universe checks with the committee first.  I'm always looking for new product recommendations  

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