The Dark Energy Delusion | Claudia de Rham Public Lecture

In The Dark Energy Delusion, theoretical physicist Claudia de Rham explores the mysteries of gravity and the universe's accelerated expansion. She discusses Einstein's theory of general relativity and questions conventional views by addressing the problem of dark energy and proposing an alternative perspective on gravity’s reach.

De Rham takes the audience through the cosmos, questioning whether gravity truly has an infinite reach and highlighting recent advancements in theoretical physics. She emphasizes the importance of upcoming experiments that could reshape our understanding of the universe.

Perimeter Institute (charitable registration number 88981 4323 RR0001) is the world’s largest independent research hub devoted to theoretical physics, created to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos.

[greenstripeypaint]

Claudia has an amazing gift for making me think I understand what she is saying.

[evelynnwinter]

The theory being proposed here sounds like a sub-type of Modified Newtonian Dynamics (MOND) whereby the argument is that gravity operates differently at different length scales. From what I can tell, most physicists don't put any credence into this theory because it creates more problems in an attempt to solve only one problem (gravity) and isn't supported by the corroborating evidence (CMB power spectrum, etc.). She is basically arguing that the graviton (which likely exists but has yet to be discovered) should not be massless (she compared it to the weak force bosons W+/- & Z and the Higgs scalar boson). Massless particles must travel at the speed of light; particles with mass cannot. Massless bosons have inifinite range (i.e. photon); massive bosons have finite range. Her proposed theory is controversial to say the least. Gravitational waves as predicted by Einstein's field equations travel at the speed of light. The advanced LIGO observatories have documented numerous events by now; one would think that news of the signals traveling slower than the speed of light would have made world headlines. Granted that LIGO is not sensitive to most frequencies of gravitational waves. Recently there was also a massive and impressive paper on using a Pulsar Timing Array (PTA) to study gravitational waves of all frequencies; nothing from that study that I recall mentioned anything about those waves traveling slower than the speed of light. She is correct in stating that the future planned LISA experiment would be more sensitive and would provide an important rule out, though the PTA study essentially used a naturally occurring apparatus that is far larger in size than anything LISA could achieve. It truly would be surprising if LISA's future data didn't align with LIGO and PTAs. I should also mention, that most physicists (from my understanding) believe that the vacuum energy is the leading candidate for what dark energy most likely is.


*Note: this impression is just based on this public talk; I have not read her published work(s) on this.

[PietroColombo-emmz]

It's a great satisfaction for a common man like me, to be able to understand the whole presentation, from a scientist of her level. Thanks professor De Rham and Perimeter Institute. 💐

[williamjmccartan]

Always appreciate that the Perimeter Institute shares these lectures and thankful that all 3 levels of government in Canada support their research, thank you

[JesseStiller]

4:32 RIP that mans phone (in the lower right corner)

[angusmackaskill]

Whenever I think about gravity it brings me down

[dsee]

Professor De Rham is certainly a great teacher, she made such complicated subject approachable by laymen.

[jedgrahek]

Awesome! This is the kind of 'outside-the-box' thinking we need more of in theoretical physics. Thank you!!!

[funjuan]

If only gravity isn't so weak and is readily detectable, we can know where everyone and everything is at a given moment in time. Just imagine the implications. We will solve every mystery of the universe. We will know who was with who. Murders, robberies, infidelities, and everything that goes on under the sun is known. Of course, we will need several hundred supercomputers for this. AI will have a field day. Maybe the pretty Dr. De Rham too.❤🎉😊

[biroskinhaa]

Thank you! I'm an undergraduate in physics, and I've been struggling to decide which field I'll pursue in my masters. This video gave me a lot to think about

[SnackFatson]

22:20 you get this animation if you think a particle wave moves up and down like open water, and not back ad forth like the tide.

[bryancrosby]

How wonderful, I have never even considered the possibility that Gravity had a finite range. But now after prácticing physics for 50 years, I can not unconsider the possibility. The more we know, the more we discover how much we did not (or do not) know

[Robinson]

Sounds like she is the Max Planck of gravity: she quantised its reach

[Fuliginosus]

Who else noticed that some of the equations behind the speaker contain errors?

[brianpcox]

I feel like dark matter is the leftover stretch of the fabric of space-time, that's wicking matter along itself like water up a papertowel. Heat death is the ultimate distribution of all things along the fabric. The universe will "dry out."
Gravity could've been the 1st force, so concentrated that it forced the other forced together. All the forces are working against the wicking effect. Whatever it takes for matter to stay together and not dissipate.

[tedwalford]

If it's recognized that "empty" space is filled with something, the Higgs Field, then we can no longer make fun of the idea of a universal aether. In fact, it could be that very aether that limits the speed of light, preventing it from being instantaneous, which is a very good thing.

[jimmimak]

This is how I understand gravity, any cosmologists or quantum physicists out there feel free to correct me: space-time is fluctuating with the quantum vacuum energy or Higgs field, which interacts with mass via the Higgs Boson. All energy and matter is just different ripples and twists and distortions of space-time, starting with photons, quarks and gluons, going up to electrons and protons and all the other particles. Put more mass or energy into an area of space-time and all the ripples and twists from that mass stretches the space-time more. It's like poking the middle of a piece of spandex held in a taut frame, except it's in 3D. This distortion of space-time and the interaction of Higgs Bosons with mass is what we call gravity, or inertia (same thing). The quantum vacuum interactions are sort of "tugging" on the mass as it tries to move through space-time; the more mass or more dense the object, the more it tugs so it's harder to accelerate or decelerate. The space-time distortion causes objects to appear to be attracted to each other, without the distortion we would be thrown off the Earth's surface and the Earth would leave the Solar system and go in a straight line.

The faster you travel through the vacuum energy, the more energy it requires to accelerate, because you are interacting with more vacuum fluctuations the faster you go, hence the limit of the speed of light. For the person travelling near the speed of light, time seems to pass slower than for people who are stationary (special relativity). Near to a large mass like a black hole, time passes more slowly compared to being at a galactic void (general relativity). Where space-time is stretched or where you are moving very quickly there's less time passing.

At the same time as all that is going on, space-time is also expanding, so that piece of stretched spandex is growing from every point in space. This causes light to red-shift because the wavelength has stretched from blue (short wavelength) to red (longer wavelength). It also means galaxies are generally getting further away from each other, so one day we won't be able to see them anymore.

Extremely large galaxies seem to be held together too well, and rotate too quickly on the outer edges. They should fall apart based on our current physics, and based on the amount of mass observed, but they don't. This led to a band-aid being applied called dark matter, which adds the missing mass back in, and we just say it's invisible. To explain the expansion, we made another band-aid called dark energy. These band-aids are a source of contention because there's so far not much evidence they exist, and it's probably more likely that our physics is wrong (The Crisis in Cosmology).

[NeilRieck]

I had the pleasure of attending this lecture in person. Also, I am a CBC junkie so appreciated the interview with Nahlah Ayed (CBC: Ideas and Ideas in the Afternoon)

[annanelson]

All you smart people in the video and in the comments give me such a burst of joy. Keep thinking😎

[pspicer]

If there is a Planck length, I don't see how gravity could be both continuous and have an infinite extent.