This Is Why Dark Energy Is The Biggest Unsolved Problem In The Universe
“The true fact of the matter is that, observationally, dark energy is behaving as though it’s a form of energy inherent to the fabric of space itself. WFIRST, NASA’s flagship astrophysics mission of the 2020s (after James Webb), should allow us to reduce the measured constraints on w down to the 1-or-2% level. If it still looks indistinguishable from a cosmological constant (with w = -1) then, we’ll have no choice but to reckon with the quantum vacuum itself.
Why does empty space have the properties that it does? Why is the zero-point energy of the fabric of the Universe a positive, non-zero value? And why does dark energy have the behavior we observe it to have, rather than any other?
There are an infinite number of models we can cook up to describe what we see, but the simplest model — of a non-zero cosmological constant — requires no additions or modifications to match the data. Until we make progress on understanding the quantum vacuum itself, dark energy will remain the biggest unsolved puzzle in all of modern theoretical physics.”
Since 1998, astronomers have known that the Universe isn’t just expanding, but that the more distant a galaxy gets from us, the faster it appears to recede away from us. The reason for this isn’t because of motion, but rather because there’s more than just matter and radiation in the Universe; there’s also a form of energy that appears to be inherent to space itself: dark energy.
While it may be theoretically fashionable to concoct new fields, modifications to gravity, or other forms of new physics, it’s unnecessary. What we really need to do is understand the quantum vacuum, and we don’t. Here’s the story so far.
Ask Ethan: Can A Laser Really Rip Apart Empty Space?
“Science Magazine recently reported that Chinese physicists will start building a 100-petawatt(!!!) laser this year. Can you please explain how they plan to achieve this, and what unique phenomenon this will help physicists explore? Such as, what exactly is “breaking the vacuum?"”
As we strive for the greatest frontiers in physics, that always means pushing the limits. To that extra digit closer to absolute zero, the extra factor in high energy particles, the extra depth into the distant Universe. Or, in the case of laser physics, to that extra intensity: power focused into an extremely narrow space. There are three things you need to up that to the maximum amount possible:
-the most extreme amount of energy,
-in the shortest-span of a pulse,
-focused on the narrowest area possible.
If you can make it all the way up to a high enough energy, you should be able to rip electron/positron pairs out of the quantum vacuum (empty space) itself. Colloquially, people have started calling this “breaking the quantum vacuum,” but in reality, nothing gets broken.
The scientific truth is far more interesting! Come get the full story on this edition of Ask Ethan!
The Four Scientific Meanings Of ‘Nothing’
“How does spacetime emerge at a particular location, when there’s no such thing as space? How can you create the beginning of time if there’s no concept of something like “before” without time already existing? And where, then, would the rules governing particles and their interactions arise from? Does this final definition of “nothing” even mean anything at all, or is it just a logical construct with no physical meaning of its own?”
We talk about nothing all the time, most often as the polar opposite of something or anything. But when it comes to the idea of physical nothingness, even scientists can’t agree on a single definition. There are four ways of speaking about the concept of nothing that scientists use all the time, and they’re extremely different from one another. Some use it colloquially, simply referring to a time at which their thing of interest didn’t exist. Others mean the Universe, as it is, removed of all matter, radiation, particles, and even spatial curvature. Some would go a step further, and ensure that the empty space of nothingness is in its ground, or lowest-energy, state. And finally, some would do away with space, time, and the laws of physics altogether. But which one of these can lay claim to truly being nothing, and how far can you go before what you have has nothing to do with reality any longer?
These are not easy questions to answer, and so I’d rather present the four scientific meanings, the context in which scientists use them, and how to identify what’s being said. After all, isn’t the point to increase our understanding?