We bet that our favorite theoretical physicist will pull through but here’s her own account:
If we leave aside gravity, we can’t measure absolute energies. We only ever measure energy differences. You probably remember this from your electronics class, you never measure the electric potential energy, you measure differences in it, which is what makes currents flow. It’s like you have a long list of height comparisons, Peter is 2 inch taller than Mary and Mary is one inch taller than Bob and Bob is 5 inch smaller than Alice. But you don’t know anyone’s absolute height. Energies are like that.
Now, this is generally the case, that you can only measure energy differences – as long as you ignore gravity. Because all kinds of energies have a gravitational pull, and for that gravitational pull it’s the absolute energy that matters, not the relative one.
So it really only becomes relevant to talk about absolute energies in general relativity, Einstein’s theory for gravity. Yes, that guy again. Now, if we want to find out the absolute value of energies, we need to do this only for one case, because we know the energy differences. Think of the height-comparisons. If you know all the relative heights, you only need to measure the absolute height of one person, say Paul, to know all the absolute heights. In General Relativity, we don’t measure Paul, we measure the vacuum …
What’s this all got to do with vacuum fluctuations? Nothing. And that’s where physicists get very confused. You see, we cannot calculate this measureable vacuum energy-density which appears in general relativity. It’s a constant that we infer from observations and that’s that.Sabine Hossenfelder, “Physicist Despairs over Vacuum Energy” at BackRe(Action)
Experimental physicist Rob Sheldon responds,
Sabine says over and over again that the problem is that physicists confuse metaphysics and physics. Which is true. But that doesn’t mean they can stop doing it. Because Sabine does it too. It’s like complaining that news sources are biassed. Of course they are. But that doesn’t mean they can stop being biassed.
What Sabine needs to do, is pick her metaphysics and be open with it. She’s a materialist, and that’s a problem for physics. And it affects the dark energy calculation. And lots of other calculations. Including her pet “measurement of lambda” issue being a materialist factoid with no metaphysical input.
Here’s Hossenfelder on the measurement of lambda.
With your morning coffee: These specialty controversies are an interesting backdrop to the current war on math. Sabine Hossenfelder and Rob Sheldon would likely agree that 2 + 2 = 4. But survey the vast degreed hordes for whom such a statement is an instance of white supremacy and colonialism and we will see the real problem facing our civilization: Far too many people have degrees (and grievances!) but no insight into what knowledge is.