Thought it would be good to again hear about some of the day-to-day work being done by a member of the Sixty Symbols team in Nottingham!

Part of the overlooked charm in these and Brady's other videos is Brady himself. The insight of your questions draw out an already captivating engagement and let the viewer participate, drawing understanding out of some heady concepts. What is your background, Brady, that you always see and pursue the 'smoking gun' in any topic, anticipating the clarifications we ourselves would seek? Thank you for all you and the faculty do and share with us!

"Time only exists for a finite period of time!" Indeed!!! **puff puff pass**

This is very interesting but looks like way too much complex to be reduce in one single video : could we have more of it ?

I was kind of hoping he say that the number is 42 ...

This video was INTENSE, and Brady's questions brought life to this interview!

Man, I wish you'd post longer videos more frequently of just you casually chatting with the different physicists. It's just so fun to watch/listen to.

This kind of reminds me of the problem of measuring a coastline: if you take a satellite photo of a coastline, and then measure the length of the coastline, the answer you get will depend on the resolution of your satellite photo. As your resolution increases, the measured length increases dramatically because you're seeing more and detail (small twists and turns in the coastline, rocks, pebbles, grains of sand, etc). In essence, the coastline is a fractal. Could it be that something similar is at work here, and that's why you get different answers for the vacuum energy depending on the scale at which you're looking? Could it be that the structure of spacetime is fractal as well? (Disclaimer: I am not a physicist, I just like reading about it)

What an awesome video. More, thank you very much! In the end you're talking about infinite universe leading to a scenario where the particle mass would reach zero. However, a question remains! Why isn't the dark energy acting as an endless, static source of energy for the particles, even in an infinite, open universe? Why the mass of particles would instead be zero (or infinitely close to the threshold of zero?) and not the other way around, meaning near infinite energy? Although that leads to the scenario that I've thought to be the very logical reasoning why an open universe just isn't a valid option. I've always thought that the reason why our universe cannot be open, is the fact that we have dynamics present in the universe. If the universe indeed was open and infinite, we'd have infinite amount of energy in infinite space - causing a scenario where the universe would contain a set, constant amount of energy everywhere. Meaning, no matter where you turn, you'd see the same flat amount of energy everywhere. Instead our observations, eg. cosmic background radiation, tell us that there indeed are local dynamics present, meaning lumps of matter, energy and the lack of those.

Is there an unedited version of this on another one of your channels somewhere? I'm very interested in hearing the full interview.

It is nice to see videos explaining actual research! It would be better if this were to be extended to include even more technical details!

keep episodes like this coming please

Love that you take your work to the pub!

"Time only exists for a limited amount of time." That seems somehow circular

OK. Got the video paused at 0:00. I've read the title, noted the running length, and strapped myself in. Lay it on me!

Before watching this video I thought that I was starting to understand some bits of quantum mechanics. This field is definitely focked op

I am hoping to become a physicist in the future which deals with the maths of fundamentals rather then than 'stretching springs in a lab'. Does anyone know what would be the best path to go down/degree to take, e.g. physics, maths, maths with physics etc. Any help would be appreciated.

Always a highlight to hear Pad being passionate about his work and it's a delight of the few times I get to be lectures by him in the public houses of Formby! Mackie.

does a vacuum have any energy? it depends if it's plugged in or not!. ba dum tssss

Thanks for leaving your questions in this time, Brady. Grey was right. You are an incredible interviewer. And Tony, as always, was an excellent respondent.

I love the banter between these two!

On the note of Brady's comment about an unstable house: So you have an unstable house that leans. You predict 3, which means you mean three beams support the leaning side of the house to make it level. You then test that hypothesis: you make sure its consistent with everything you already know, you test it on a small scale, then if the scaled version was correct, you go for the full fix. If it works, your hypothesis was right; if it wasn't, its wrong. However, something not mentioned is lets say you've used this hypothesis before on similar problems and its worked before, even when you predicted exactly how many beams you needed. That gives you confidence in your system, so you then apply it to unproven areas and either find it consistent or inconsistent. If its then inconsistent, you know your system works for some problems but not others. If it is consistent, you know you can continue to expand the kinds of problems you can apply your system to. However sometimes when you're inconsistent, you were partly right so you suspect with some changes to your system it could be right, but you need to keep it consistent with everything you already know and you have to prove its a correct assumption. You can also choose when to apply certain systems, but I'll get into that later. That is exactly how science works. We have these equations which have been very correct and useful in some areas, unsuccessful in others, and we are running into new problems which look like they could fit with our equations if we teak somethings. We ultimately have to prove our assumption is correct by testing it, and we eventually have to seek a state where we can use one equation and not pick and choose like we do right now, AND we might not have the ability to currently test some of our assumptions, but with how successful theoretical physics has been in the past 5 decades, with the prediction and discovery of things such as the higgs boson and the like, we will continue down the path of tweaking old ideas and running with them on the hunch that they will prove to be correct in the future. Sometimes we're right and sometimes we're wrong, but we often know our limitations and have been very successful in the past 100 years. On the note of Brady's comment and Dr. Padilla's statement about universally applying equations: If the equations work on the scale limitations you have, they work. Science will ultimately prefer a state where all equations agree and there are as few as possible, but science is usable. It's usable because when you're shooting a rocket to the moon, you only need to know pi to 6 digits and quantum physics never figures in to your calculations. Most things built on science that humans depend on are justified with equations that are limited but no less correct on a near perfect level. There have been things built in the pass that failed on a hunch, but with the progress humans have made since the enlightenment, we benefit more from trusting theoretically justified opinions than we loose.

Absolutely fascinating and brilliant!

Vacuum energy is easy to measure, just look for the wattage on the bottom of the vacuum cleaner.

Nice Video !! Hope to see more of these types.

Hi Brady, I'd request you to make one more video of this as many people here including I haven't fully understood the implications and reason for this cosmological constant. Thank you :)

does the vacuum remain constant or does it vary like barometric pressure?

I'm intrigued but confused, so a couple of questions: - If you have both the spacetime size of the universe and the vacuum energy as unknowns in your equation, how can you say anything about either of them? - If you can measure the change in vacuum energy by varying the distance between two plates, why can't you use that data to extrapolate to the real vacuum energy? - If you know the different correction factors at different scales, can't you calculate them at lots of different scales and figure out how it's a function of scale?

Do these values added in to cancel out numbers have any relation to antibonding in molecular bonding theory? I kind of understand that you have to add in a value in order to have matter/energy conserved.

If this idea is correct does it predict subtle changes in the mass of distant (and hence: early) galaxies? Would we be able to test the idea through observations of gravitational lensing?

I have a big problem with vacuum energy and it drives me nuts. The way I was introduced to the subject was in terms of decomposing fields into harmonic oscillators. Each of them has zero-point energy and because QFT has infinite degrees of freedom, you get infinite vacuum energy. You can introduce minimal distance, the Plank length. to make energy density finite, but that is still huge. The problem with this picture is, you're measuring zero-point energy from the bottom of the potential well, and that's as good a place as any, due to gauge symmetry. But ultimately energy is just the ability to do work, and you can't extract any work out of an oscillator being in it's ground state, so the vacuum energy should really be zero. However, that kind of vacuum is an eigenstate of particle number operator, so there should be no fluctuations in number of particles. The fact that there are suggests to me that the "real vacuum" is not really vacuum in the sense of no particles.

So, anyone up for dinner in the Restaurant at the End of the Universe?

On the ball with good questions today Brady.

This was very, very abstract, I only got some of it. One question though: If the time the universe will last is linked to the vacuum energy, and the vacuum energy is constant, does that mean the total age of the universe was set from the beginning? And is that information contained within every point in the universe?

If the mass of all particles in the universe "talks" to the cosmological constant then does this imply the Higgs Mechanism is responsible for the curvature of spacetime? Correct me if I am wrong but the cosmological constant is a "mathematical fix" to the problem insofar as it does not describe the physical nature of what the constant is. The one problem I see is that if particle's masses are communicating with the cosmological constant over all of spacetime then the constant at some particular point in spacetime can't know of all the particle's mass in the universe since the information only propagates at c. Does this imply that it cannot be constant?

Does anybody know which books should l be reading first in order for me to be able to understand the papers in the description. (hopefully it wont be like 40 books that take 12 years to read) because l'm interested in really understanding those papers.

excellent episode, I love stuff like this

I like this video very much, I learned a lot!

This is amazing.

Dr. P talked about particles with zero mass. Did he (and the other researchers in the paper) take interaction with the Higgs field into account? From what I understand (which could very well be incorrect), interaction with the Higgs field is what "gives" particles mass. Could this have an impact on their findings? Maybe feature the value of the constant on Numberphile?

This was a great video. I love videos that are all about current cutting edge research and theories. So does this theory completely rule out a hyperbolic or flat universe? Does it have to be spherical? Or is this prediction completely unrelated to that question? Because, if I understood correctly, a spherical universe would be one which has such a big crunch, while a flat one would have a heat death and a hyperbolic one would just expand indefinitely, right? This channel has reached that level multiple times already, and so, if I recall correctly, have Numberphile, Periodic Videos, and Deep Sky Videos. However, I can't quite say that about Computerphile. I hope that one will get there soon too. (Right now it's pretty much "just" covering the basics. Which, I guess, is fine, since it's a younger channel) TL;DR please do more day-to-day-work. Across all channels :D

I always love the stuff written on the boards in the background. this one is great, so simple. wonder what the discussion was about that led to that drawing.

Can you do a video that compares the ideas of the big crunch and the big rip?

Another question i do not know if it make sense or not Tony said we do not know if the dark energy is uniform spread or not over the universe. Since it do exhibit a force would a change in the dark energy "pressure" affect the decay rate of any material above tinn? I heard htat at periodic videos that all material above was slightly radioactive? So if the inflow/density of dark energy thins out we would live in a slight more radioactive world?

As an accountant performing complex financial consolidations involving multi-currencies, I am always left with a "difference" between the left hand and the right hand sides of the ledger. How is this resolved? Very easily - if the left hand is bigger than the right, I insert an ad hoc "plug" in the right hand (or vice a versa if the right is larger than the left) so that both sides balance to zero. That, I suspect, is all what Dr. Padilla is doing when he talks about inserting an ad hoc number to cancel the energies and bring it all back to zero. QED!

AMAZING CAMERA WORK

if you were able to tap into vacuum energy , after you used it for whatever purpose you used it for, would it be put back? how would it be put back and converted back to that form of energy?

Q : in the initial part of the vid there are particles popping in and out of existence... if i take one of em to be an electron the other shud be a positron rite? then after they annihilate why is thr a flash of light/energy? shouldn't the total energy of that system remain 0? cancel each other stuff? i've seen it in some feyman diagrams too... are they wrong? somebody help! :( they = the diagrams i saw...

You were clear that your theory predicts an end to time. Does it also predict that the universe is finite in spatial dimensions too? Also, what do theoretical physicists think about that issue? Do most of them believe the universe is likely infinite? Or do they mean "for all intents and purposes, infinite, but really finite"? Or is a universe of finite size (spatially) currently preferred? (I'm not just talking about the observable universe here, by the way.)

I find this video, the associated papers, and the potential implications to be fascinating. Even some bits of these propositions, if true, soundly refute the long-standing idea of a heat death for the universe. Particles spit out energy that makes the universe expand, filling it up like a balloon, until they can't anymore. With nothing left pushing out, it all slams back together to start again. (Assuming, I guess, that reality is a closed system, so no energy is lost as it goes about this stuff, and so the process can't ever peter out.

WOW. Dr. Padilla has clearly spent a lot of time thinking about this model; the way he explained it was brilliant. Also... "I couldn't just say... okay... number 3, and everything's better;..." HA!!!!!!!!!!

Can you say that the amount of "Counter term" needed in an equation is like magnifying a picture? That the value of counter term is the percentage of zooming basically Here's how I reasoned: The values differ from scales (atomic -> subatomic etc etc), because you "zoom" in more and thus see more particles which has energy? Kind of like if you had a few big stones and a few small grains of sand on a table and you were to measure the mass of them. But since the grains of sand were to small for you to measure, they got left out (and thus missing out on some mass). But if you were to measure more closely you'd see those grains of sand and record them which would basically get you more mass just by zooming in. Can you say this is a correct way of thinking about the counter terms?

Why are you able to get different energy values at different levels? Wouldn't it all be giving the same value throughout? I don't understand.

This whole video went straight over my head.

Wow. I don't think that I really get it but that was really interesting! Keep up the good work! Both of you :)

if this is correct then space should be positively curved and not flat like observations have shown and must of required energy to come into existence. So there must be something wrong with the current model of the universe or have I missed something?

What I find crazy is the universe is expanding faster than light, and light itself takes light years before it reaches earth from nearby stars, so intuitively it leads me to believe the universe will end far before we even realize it, or may have even already ended, and the laws of physics for the universe may have already changed to accommodate those conditions at that point in space and time, but we just haven't caught up with it yet and we're just existing in the past. I think my mind just crashed, and it's temperately out of order.

If this really predicts the end of time this would also predict the end of space so the universe is not infinite but finite . So my question is given the cosmological constant and the mass of particals and given the age of the universe can it be possible to predict the overall size of the universe at present?

The difficulty of measuring the vacuum energy seems very similar to the difficulty of measuring air pressure. At least on an everyday, human scale you can really only measure differences in pressure. You need a chamber with (close to) vacuum for comparison in order to measure the true air pressure where you are.

What's the really complicated looking diagram on your board?

Does this imply that during the early stages of the Universe and Hyper Inflation that the masses of the particles were HUGE? Does this make sense to relate the mass of particles to the Space-time of the Universe?

exactly what does he say at 1:53-1:58?

Maybe I'm talking out of my arse here, but if the Casimir-Effect is the change in vacuum energy as the boundaries of the vacuum change size (the space between two big plates), then couldn't the same thing be happening as you scale up the boundaries of the mathematical "simulation" when going from microscopic to macroscopic level of detail? Or is Wikipedia right in this case (instead of the professor being right) by saying: "Thus [the Casimir effect] can be interpreted without any reference to the zero-point energy (vacuum energy) of quantum fields."

just wandering, maybe because I'm not understanding this deeply enough, (would love to get an answer), can"t you just come up with a mass constant that allows for mass to exist in an infinite universe, exactly like the cosmological constant allows a universe bigger than the moon to exist despite vacuum energy?

At 4:14 what does he say so fast ?? The ?......? (in?)stability ?

I justed watched a talk on the interpretation of quantum physics, and I think they had four theories up for discussion, e.g. susy, many world, etc - and on susy they said that the LHC results actually indicated there may be no such thing, after all. Maybe you can say a few words on that in another vid?

5:51 Precisely. The mere fact we need that cosmological constant to make our description of nature 'right', hints at some underlying reality we don't understand or even don't know anything about yet. Which means our description of nature, as it is today, must be incorrect or at least particularly incomplete. In my opinion, we haven't yet begun to understand 'the true nature of nature'. Which is of course good news for the boys and girls working on physics and mathematics, who will not need to worry about unemployment for say the next 20 or 30 centuries, as there is still some immensely interesting work on the shelf and some Nobel prizes to be won.

Sometimes I think I should have finished school...could have had a better job, more money, etc. then I see videos like this and no wonder I stopped going to school. This is all way to hard to grasp.....aaaaaand science is my favorite subject.

The number is 42!

Do your calculations distinguish between a universe that's finite in space and a universe that's finite in time?

I have a question. Check out the equation at the beginning. What does it mean when the differential comes right after the integral sign, followed by a long string of variables? In this case, I am talking about what looks like Int(dⁿx∙√g·...

Let me try to explain the cancellation how I see it. Take x+3=5, you can look at this and know that it has to equal five, and that you have to add a three, so you feel perfectly safe in subtracting 3 from both sides, aka cancelling three. So if I call v the vacuum energy, E is energy, and U is the universe, then we get the sample equation E+v=U. We can observe the universe and know what our "5" is in this case, and we can estimate how much energy there is outside these vacuums. So when they cancel the vacuum energy, they just subtracted their "3" because our measurements have to equal the universe in the end.

I heard that from recent calculatons the universe seemed to be accelerating its expansion, nullifying the Big Crunch Theory, isn't that right?

the opposite of vacuum is pressure. couldn't it be so that mass of the stars and planets exercing gravitational force creates that vacuum? To calculate the value of this vacuum, one would need to estimate the mass of the entire universe and calculate the amount of gravitational force. It would also explain the difference in vacuum as a relation to the proximity to gravity clusters such as galaxies, black holes etc.

I don't know what I prefer now. I was just getting used to the idea of an infinite universe due to eternal inflation models now we go back to the old ideas of cyclic big crunches. Infinity blows the mind, but then again so does a finite space not embedded in anything. Not to mention the infinities of singularities.

Why has there never been a dedicated sixty symbols video on supersymmetry? I would be interested

I don't quite get why the universe would end because of this. To my understanding, gravity should "dampen" the expansion of the universe (it's still accelerating though). If the particle masses go to zero at some point in the future, what else would be there to cause a big crunch? Couldn't it be that we just happen be in that very active epoch of the (young) universe and it just continues to grow until the energy density is infinitely close to zero? Why would everything collapse again?

Can someone please explain to me how our discovery of energetic particles blinking in and out of existence...and the claim that energy can neither be created or destroyed...are suppose to co-exist without contradiction?

How can things put in and out of existence, what about entropy, I thought it can only go 1 way.?

Does Planck apply to gravity, ie, quantum fluctuations smaller than Planck wouldn't matter?

He assumes that particles have mass. what kind of mass? according to string theory, for example, the mass comes from vibration energy. Is that still considered mass?

How "constant" are constants in reality? Can, say the mass (or charge) of an electron, very at the nth decimal place from electron to electron? And I don't mean our ability to measure. I mean in principle, like a corollary of Heisenberg's Uncertainty Principle.

ok, somewhat silly question: his argument for why we can't measure the vacuum energy locally is that we have no way to ensure that whatever we're measuring locally is constant at other scales... why does that same logic not apply to other "constants" that we measure, like G or c? Couldn't they also be different somewhere we've never tried to measure them?

He just calls it a vacuum energy , lightly talked about the the Casimir effect. But he only called it an ambiguous "cancel number",which I do agree with, but in the Caismir effect its called "negative pressure" and "positive pressure" and the energy that is generated is created from disturbing this balance, which a pressure unit is normally talked about as Torr level or PSI, but does not venture out into the negative realm nor does E=mc² which c² is light in a vacuum or 0. If light enters into positive Torr levels its warped and slowed down(same speed longer path), if given a negative Torr level is it also warped and slowed down(Here is the theoretical part. ) in an opposite path and the disturbance created from a + and - Torr level, let you make use of this vacuum energy (aka warp bubble). Would like to see experiments testing this.

OMG everything makes sence now, almost. Thank you, I have teories of my own but this one is great. lol.. xd

What if the predicted huge vacuum energy is there; just manifested differently at different scales? Perhaps as the forces themselves. Instead of "force carriers" matter simply interacts with the vacuum energy in slightly different ways at different scales. I personally find the entropic interpretation fascinating where dark energy is simply gravity at a larger scale.

What is the universe expanding into?

I'm wondering, how does this relate to the Poincare recurrence time? Are they one and the same?

I try to combine the cosmological constant and the schrodinger solution on the planck scale. I used planck units. At the end I went back to SI units to compare with the measured vacuum energy density (0.63 10^-9 J/m^3.) Combine: 1) Einstein, cosmological constant 2) Schrödinger solution 3) Planck units Result: - vacuum catastrophe solved? 1)Einstein, cosmological constant Λ = (8π 𝐺 ƐΛ)/(𝑐^4) Planck units: G=1 c=1 Λ (6.1871424 10^34)^-2 = (8π ƐΛ [planckEnergy/planckVolume] 1.1056 10^-52 (6.1871424 10^34)^-2 = 8π ƐΛ 0.001149 10^-120 = ƐΛ 0.1149 10^-122/ ƐΛ = 1 2)Schrödinger solution, n=1 (ℎbar^2 𝑛^2 𝜋^2) / (2𝑚𝐿^2) = E Planck units hbar=1 n=1 m= mplanck =1 L= Lplanck=1 0.5 𝜋^2= E 1= E/0.5 𝜋^2 3)Einstein, Cosmological Constant = Schrödinger solution 0.1149 10^-122/ ƐΛ = 1 = E/0.5 𝜋^2 0.1149 10^-122 0.5 𝜋^2= ƐΛ Eplanck Eplanck =1 0.1149 10^-122 0.5 𝜋^2= ƐΛ 0.567 10^-122 = ƐΛ [planckEnergy/planckVolume] 0.567 10^-122 1.9561 10^9 /(1.61625502 10^-35)^3= ƐΛ [J/m^3] ƐΛ = 2.627 10^-9 [J/m^3] Measured: 0.63 10^-9 [J/m^3] I am looking forward to your response.

I had to come back to this video several times. So basically what the professor is saying that the end of the universe will indeed be a Big Crunch. So the idea that through dark energy the universe will for ever be expanding with all matter being pulled apart is not correct. In my own mind I have wondered about this because of space-time that was created at the point of the Big Bang so however the universe will end space-time has to end with it. Am I right my own mind?

Great explanation of this model of the universe especially the end which is very interesting yet isn't there evidence that the universe is infinite through geometry using the cosmic background? Btw a universe from nothing is a great read about this topic in my opinion

This sounds extremely powerful

He said the space time volume can't be infinite or the mass of particles would be zero, so why can't the universe be finite and time infinite?

So let me get this straight... firstly the increasing expansion of the universe will somehow still result in a big crunch? And secondly in quantum mechanics it's ok if your theory gives an answer that doesn't match the data, so long as your fudge factor consistently gives the right answer? How is that different from drawing your curves before plotting your data?

A couple of questions... 1) What's on the board to the left of Tony's head? Looks like a really ropey Feynman diagram. 2) how do particles know the universe is not going to be infinite? They wouldn't know until it ended. It seems the armageddon theory and the massless particle theory actually describe the same (effective) outcome-nothing.

What I got out of this was "there's this observable phenomenon we can't explain and for which we don't have any logical justification, so we're just going to invent variables until our current math/theories make some sort of sense again". Seems to me this denotes a more fundamental misunderstanding of the forces and physics at work, rather than some undefined "dark energy" or cosmological constant to be pinned down. Back to the ol' drawing board? Brady, please do another video on this subject as more discoveries are made into this particular field; I for one and interested in hearing more on this as we come to better understand what's really going on.

why can we just "cancel" out some number because it doesnt work with our current theory and measurement. Is it not surely an indication that we dont understand something and considering a value to counter-act what we dont see is not really solving the problem as to where that value comes from?

The gravitons travel at the speed of light right?? If we can see the light of young universe why can´t we feel the gravity of young universe, and why that force can´t be the dark energy? Can somebody answer me?? (My english is not very good because I am learning yet)

This time Brady totally disrupted the explanation. Maybe those nitty-gritties should fit another video; or maybe a few lifetimes of videos, if he wants to go to subatomic levels of details (pun intended). Please! I beg you! At least let him give us the abstract before cutting him off next time?

Just last week saw a video here on youtube that said one day something to do with the Higgs field will change and all matter will change, we are in a slump of time where things are all the way they are but eventually it will change I guess it was particle wise. So all things will I guess in a way fall apart I am not really sure it wasn't clearly defined. Visually shown as a graph declining from the top left and in the middle the slump occurs and that is now then with a slight rise following this period the graph drops again. That is when things change. So basically it was like a waterfall that falls twice where halfway down it hits a surface and digs it out before flowing onwards, upwards and ultimately downwards. We are getting pounded by the first fall essentially.