29 Subatomic Stories: How will the universe end?

[@redims8967]

Hi Dr. Lincoln! I just wanted to say thank you for taking the time and resources to answer my question on the hoopla of the Higgs Boson. Thank you for being a wonderful science communicator!

[@jameseproctorpmp]

Space is expanding faster than the speed of light from us anything beyond about 13.2b light years. We know that space expanded slower than 74 kilometers per second per mega parsec before about 4 or 5 billion years ago so it might be slightly further than 13.2b light years. Light travels at approximately 300,000 kilometers per second. We know a mega parsec is 3.26 million light years. If you calculate the speed of light and the expansion of space, the point where space is expanding faster than the speed of light is around the beginning of the universe so we can see the cosmic background radiation and many of the first galaxies. We are living in a great time because if we were alive one billion years from now, all of the early galaxies would be beyond the cosmic horizon. We also know that the universe itself has expanded at least to a radius of 46 billion light years from earth. At those most distant areas of the universe space is expanding over one million kilometers per second away from us which is more than 3x the speed of light.

[@42Hz]

Dr. Don Lincoln, thanks so much for the interesting video! Really grateful for explaining Dark energy once again :)

[@sebastjanbrezovnik5250]

I could listen daily to this stuff. Thanks for taking your valuable time for this, much appreciated.

[@paulfrancis8836]

Your the best. You don't look down on less learned people. You try to bring them up to date, and that's very much to your credit. If my old Math teacher did the same. I'd be a genius by now. Your the True meaning of a teacher.

[@juijani4445]

I like how John A. Wheeler puts it: Matter tells spacetime how to curve Spacetime tells matter how to move.

[@KasiusKlej]

"Keep curving left" said Saturn's moon to spacetime "so I can go straight as I always do." "You're going as an asteroid belt from now on" said spacetime to the moon.

[@wulerhaufung9468]

relationship goals

[@juijani4445]

@spaghettarius a Then what about a stationary object (0 acceleration) ? Oh and by matter, I also meant energy cause matter and energy are both in fact equivalent according to Einstein.

[@juijani4445]

@spaghettarius a But if I were to take an isolated system consisting of 2 massive objects of equal mass (say A and B) orbiting each other as in a binary system and then having an object of lower mass as compared to those other 2 (say C) right at the neutral point of A and B then wouldn't C curve spacetime even in an isolated system?

[@juijani4445]

Also, I get that concept where you have to dive into nuclear physics where some of the mass of the nucleons goes into the binding energy required to keep the nucleus stable so the total mass of the nucleus is less than the sum of the masses of all individual nucleons. Can be used as an analogy right?

[@michaelblacktree]

_"So this is how the universe dies... with thunderous applause."_ --Queen Amidala, probably

[@sapelesteve]

Yet another excellent video Dr. Don. Gotta love these theoretical discussions. For me at home it's "Subatomic Stories Is Everything"! 😉😉👍👍

[@SabbraCadaver]

Great video, however I think it would help if you clarified that objects beyond the observable universe aren't *moving* away greater than the speed of light (i.e. v>c) at 12:53. It's simply that the expansion of space between us and them increases the distance such that to catch up with them the observer would need to travel faster than c. It's a simple but important distinction that took years to click in my undergraduate days!!

[@vinicionincheri3070]

I STRONGLY recommend Flatland; funny, insightfull and incredibly funny. I stumbled upon this little gem while studying for a Linear Algebra term at uni.. Well done prof.

[@JasonJason210]

I'm always glad when I see a new one of your videos in my feed.

[@bluecaroline4407]

Thank you Dr. Lincoln! What a nice way to start my day!

[@BothHands1]

amazing explanations with the math. it's very literal; matter of fact. always enjoy these :)

[@mikeseman6598]

I liked the analogy to water freezing and how inflation could be the energy released as from the separation of the strong force. That felt so comforting... but sounded like that was over simplified or not well accepted. Thanks for the video!

[@raymitchell9736]

Thank you Dr. Lincoln for making these videos... I really like the way you explain things and bring a sense of humor into the discussion making the subject matter more approachable. I can see that you have a great passion for all things physics, but do you have a specific area that interests you the most?

[@drdon5205]

Where physics meets philosophy, and physics has actual and valuable answers.

[@raymitchell9736]

@@drdon5205 I see, you are currently making these videos with those questions... and I can see that has a huge appeal. I know you've covered unexplained physics, (love those videos BTW) Have you looked into other unexplained areas of natural phenomenon? - and I don't mean misinterpreted, but verified unexplained? I know this channel is not for that, but just curious if you have looked at it.

[@drdon5205]

@@raymitchell9736 Like what? Probably.

[@raymitchell9736]

@@drdon5205 There are many, so I will ask about one, if this is not be one you looked at, perhaps you can mention one... ~2007 I attended a talk at SRI that (and sorry, I can't recall details) presented some evidence for Lithosphere-Atmosphere-Ionosphere Coupling, the so-called "Earthquake Lights" people see as a precursor to major quakes. As I searched trying to find the details for this comment, I see there is a model: LAIC "can explain most of these events as a synergy between different ground surface, atmosphere and ionosphere processes and anomalous variations which are usually named as short-term earthquake precursors." And related? Might be the Mystery of the Brown Mountain lights in North Carolina.

[@drdon5205]

@@raymitchell9736 This is outside my expertise. I would Google just like you would.

[@jenaf372]

Yay my note got mentioned. Much love

[@Darkanight]

what a pleasant break this is

[@AlanTheBeast100]

I just got a text from my buddy in the outer rims of the 2nd bar of Andromeda. They're calling the post merger "Andromaway"

[@frederf3227]

Andromaway, andromaway, andromaway, andromaway, andromaway, andromaway, andromaway, andromaway, EEEeeeeeEEEeeeeeeEooooOOooooooo a weeumbumbahwayyyyy.

[@fnamelname9077]

@@frederf3227 I had NOOO idea what you were on about, until those eee's. And then I knew *instantly*. Hahahaha!

[@Nissenov]

@@frederf3227 in the jungle, the mighty jungle.

[@dhoffheimerj]

Thanks for one of your best lessons so far.

[@terekrutherford8879]

The diagrams for this week's questions were super helpful!

[@jhonbus]

9:49 interesting depiction of a moving jalaxy distorting spacetime with its jravity in that jif you showed us!

[@Garryvision]

Would you drink Gin whilst watching Gyrating Gifs? Steve Wilhite, the creator of the GIF format says it should be pronounced 'JIF'... I prefer the hard G, Graphics Interchange Format but hey, I didn't name it!

[@aarav_sharma]

Why are you Jay?

[@constpegasus]

Awesome as usual. Love it.

[@tresajessygeorge210]

THANK YOU PROFESSOR LINCOLN...!!!

[@Kevin-wo3kp]

Thank God for Dr Lincoln and others like him.

[@42Hz]

Question: In a very distant future, black holes will evaporate and all particles will decay. Well except for bosons probably. Does it mean that physics will change? And what will happen to the gravity?

[@jerrymiller276]

Perhaps gravity becomes "flat" and therefore un-observable?

[@MichaelDonlinAwesome]

Heck yes for the Abbott and Flatland shoutout.

[@extremawesomazing]

Delightful. Thank you.

[@arpioisme]

Lol, someone is in the room. Dr. Don is actually being held hostage

[@ChargeOfGlory]

timestamp? where in the video dod you notice?

[@ChristopherCurtis]

At 1:39 you can hear someone cracking the whip. He gives a worried sideways glance a couple seconds later.

[@thethirdjegs]

@@ChristopherCurtis Shoot. I heard another near the end of the vid. They both sound like a door instead of a whip.

[@MarxistKnight]

If you look carefully, he has arranged his books behind him so the first letter of each title reads “for the love of god, please send help!”

[@hartunstart]

Don't worry. He has dark energy in his pocket to make the room expand by surprise.

[@hamentaschen]

"These pretzels are making me thirsty!"

[@stevedixon9734]

How does charge work? An ionic bond like Na giving and electron to Cl keeps the atoms bonded. Are photons being exchanged between electrons and quarks to bond the atoms together?

[@Ebani]

Charge works by electromagnetism, nothing is being exchanged, if charges changed then the whole thing would change. Then you're mixing photons with electrons, photons are massless, electrons aren't. You need to read actual science books bc you're way confused. Photons are a form of electro-magnetic radiation while electrons are part of an atom's nuclei.

[@XEinstein]

Well firstly quarks don't interact with photons at all. The boson for a quark is called a gluon and the boson for electromagnetism is the photon. When it comes to molecular bonding the electroncloud of let's say two individual hydrogen atom fuse together. So the electroncloud has just as much probability to be on every side of each of the two atomic nucleai. And it just so happens to be that two hydrogen atoms bonded together into an H2 molecule has a lower energy state than the energy state that two individual Hydrogen atoms have.

[@Garryvision]

It is as straightforward as you say at first. In Ionic bonding, an atom 'prefers' to have a full outer shell of electrons. Sodium has one electron in its outer shell and Chlorine has one electron short of a full shell. These elements alone are neutrally charged until the electron in the Sodium atom fills the 'electron-hole' in the Chlorine atom - creating ions with different charges. This leaves the Sodium atom with a +1 charge and the Chlorine with a -1 charge (an electron has a charge of -1 or -e). This difference in the charge of the two ions is what holds them together in an ionic bond. You may have heard mention of exchange bosons (which include virtual photons) which are unrelated to ionic bonding but are an explanation given by quantum electrodynamics in relation to the interaction of subatomic particles. If you like falling down the (many) rabbit hole(s) of Physics, well worth reading up on!

[@Garryvision]

@@XEinstein This would be covalent bonding as opposed to ionic bonding.

[@gursach4435]

@@Ebani Just want to clarify that Steve correctly said that photons are being exchanged, not electric charges. From what I've learned from high school physics, charged particles (like electrons) emit photons, both 'virtual' and 'real', which mediate electrostatic forces. A common (albeit incomplete) analogy used to describe this compares electrons to two stationary canoes floating on a lake. Someone in one of the canoes throws an object with momentum (the exchange particle for the electromagnetic force, a photon) at the other canoe, and someone in the other canoe catches it, sending both canoes away from each other in order to conserve momentum. The analogy used for opposite charges was that the object thrown was a boomerang, outwards from one canoe, and it is caught on the opposite side of the other canoe, sending the two towards each other. Also, as Dr. Lincoln has said before, all particles do have a cloud of virtual particles saturating the space around them, constantly appearing and disappearing. I think that the force only does work when virtual particles emitted by one particle interact with another particle, but again, my understanding of the subject is still limited to high school physics. What I am sure of, though, is that electrons are not part of an atom's nucleus. Electrons of different, discrete energy levels surround atoms in 'clouds', on average hundreds or even thousands of nucleus diameters away from the nucleus itself. p.s. It's not really helpful to tell someone to 'read actual science books' because they're confused instead of just giving an answer yourself. Especially if you're the one who's confused.

[@Emmanuel_Franquemagne]

Regarding to Jenaf37's question, I guess it would be worth connecting it to answer to ChangeGamer, raising up that objects _seem_ to be moving away from us, but they actually don't have such motion nor velocity. Meaning, they don't have the kinetic energy relevant to such a speed. Actually, some of these objects might have their "own" velocity vector directed (so moving) towards us. But this velocity is far too low compared to their apparent motion given by the expanding space between us and then! ;-) And maybe worth explaining this doesn't violate special therory of Relativity, as it is an "emerging speed", only due to the accumulated distance between these objects and us. This is the same point than if you have a turning light ray projecting on a giant screen far, far away. The light emitter doesn't turn faster than light, but spot on the screen will seem to move faster than light if the screen is far enough. But again, there is no information transmission, each spot being causally independant from each other, only correlated by the light source. This is the same for objects moving from us, simply moving at the sum of "elementary distances" between us and them, not moving faster than light by themselves.

[@l00d3r]

I have a question. Have we considered the possibility that space, like a spring, expands and retracts. We could be in the period during which the "spring" is expanding from its contracted position (big bang), so it is expanding with an acceleration, but eventually will reach its "rest" position and start decelerating and eventually start contracting. So, like a spring that has been contracted, it expands for a period of time, then retracts for another period, then expands, etc.

[@stevenaspinwall2480]

Please correct if wrong. that the Higgs field takes in speed and gives mass. A space field could give speed and reduce mass. Here’s the key tho, the ratio of exchange happens different, going in we get 1:31 but going out might only need a 1:1. This would explain a lot I believe, probably wrong tho lol

[@wardtj]

Woah! To think on your answer of how the Hubble constant says that at 4285 mega-parsecs, things are moving away from us at the speed of light, gives some very interesting notions of what we experience in our reality. The mind bending part, is then, by definition, according to those observers WE are moving away from them at the speed of light. Am I thinking of this the wrong way? And taking this one step further, even if we are moving away from another observer at the speed of light, WE do not feel the effects of moving at light speed. Fascinating!

[@michaelsommers2356]

As stated in the video, istant galaxies are not moving away from us. Rather, they are being separated from us by the expansion of space. That is not at all the same thing as moving.

[@drdon5205]

@@michaelsommers2356 True, but it looks a lot alike.

[@michaelsommers2356]

@@drdon5205 Yes, but it seems to confuse people to say that distant galaxies are moving away faster than the speed of light. We need better vocabulary.

[@amanborasi2183]

1. is there any chance that there might be some series of big bang had already been happened before our known one? 2. can we predicted from the rate of expansion of space that its follow the sinusoidal curve or say a periodic curve,?

[@martijnvangorp]

I really enjoyed this video.

[@openohm]

I love your show. It is so nice to take a small break from politics!

[@simplyeditingtoday]

What a great episode.

[@mahipalyadav6053]

The simple answer is "we don't know"

[@maythesciencebewithyou]

Once scientists figure it out you can bet a biblical scholar will figure out a way to read the same answer from the Bible. A Muslim scholar will then manage the same with the Koran. Even later, another scientist will figure out that the first scientist made some mistakes and declare his answer to be wrong. And religious scholars will have known it all along.

[@smlanka4u]

Roger penrose has a good explanation too.

[@Nulley0]

Teachers: This is not an answer

[@whatelseison8970]

@@Nulley0 No, my answer for teachers was usually, "I don't _do_ homework."

[@jaydunstan1618]

Ha!

[@nutier]

awesome viewing ! I enjoy it so much . Yes , i agree with you so . The universe will end one time , beacause it had existed since a long time . when it will end , there will be nothing in the universe , no the Sun , the earth , the water , the air , the stars , the Aliens , the galaxies , etc. , I think .

[@zebimicion9739]

What does it mean to say all the forces were united? That gravity somehow worked like magnetism or that the weak force worked like gravity?

[@drdon5205]

Kinda sorta.

[@MilosMalinic]

9:50 Is there a kind of space elasticity? The mass curves the space, but which force/thing relaxes it after being bent?

[@cloudpoint0]

You can use space elasticity as a metaphor but it is really the coordinates of universe’s gravitation field that curve when there is mass present and then relax when the mass is gone while space does nothing and is nothing.

[@MilosMalinic]

​@@cloudpoint0 Then, why are we talking about space instead of gravitation field?

[@cloudpoint0]

@@MilosMalinic We are taught that mass warps spacetime, and the curvature of spacetime around mass explains gravity - so that an object in orbit around Earth, for example, is actually going in a straight line through curved spacetime. Mass does not curve just space or curve just time separately, in my understanding. Just spacetime can be curved although the time dimension within spacetime usually does all or most of the curving, away from black holes anyway. Time in spacetime is actually a special kind of spatial dimension, it’s not true time (it is even shown backwards in spacetime plots). Maybe spacetime should have been called the “joint space-time-gravitation field”. Spacetime really just explains how gravity varies in the presence of uneven distributions of energy, like mass. Spacetime is an imaginary thing, a human idea. It’s like the grid of longitudes and latitudes that we place around the Earth so that we can measure positions of things on Earth. Spacetime is a grid that we place around the universe. The interesting thing about the spacetime grid is we must consider it to be warped or curved in places for gravitational pulls (straight line paths) to work out in the way that we observe them to behave in the real world. There is no force doing this to the grid. Nothing is varying - the grid is static (there’s no true time dimension to let it vary). It’s just the way the geometry needs to work to be correct.

[@john-or9cf]

Rather eclectic library you have behind you, doc!

[@williamprior7831]

Quick, we need to see if he's sending us messages

[@DaBlondDude]

It'd be fascinating to a list of the books

[@tommywalker3942]

@@DaBlondDude I read The Great Mortality based on seeing it in the background recently, remarkable read. Any more suggestions for a similar book?

[@DaBlondDude]

@@tommywalker3942 Well, he suggests a few himself in these talks and the bookshelf is easy enough to read (the parts we can see). One book I suggest for anyone is Bill Bryson's "A short history of nearly everything". Another I'm reading (again) right now is Ben Goldacre's "Bad science". Beyond that I'm a bookaholic and read all over the spectrum but you may enjoy a Facebook group I'm in called 'Doctor Anna's Book Club' (she's a scientist and science explainer) where a science based book is proposed monthly, and discussed

[@DaBlondDude]

@@tommywalker3942 oh yeah, FYI the current book in that group (yes, I quite often read more than one book at a time) is "Forces of nature" by Brian Cox and Andrew Cohen. Others were 'The Selfish Gene' by Richard Dawkins, The Elephant in the Brain, etc

[@xisotopex]

I get the feeling from watching these videos that there are many more barriers to space travel than just propulsion/fuel or energy.

[@zzzzzzzzzzzz-zq9iz]

Does the expansion of the universe affect the strength of gravity? As if there was a ball on a bedsheet, and you pull the sheet tighter, the ball sits higher than if the sheet is relaxed.

[@andrewatkinson201]

it does because of the power of spacetime straching makes the ball pull tighter to the field

[@MuttFitness]

Somebody is clapping at 1:40. Is Don in trouble? Did he forget to take out the trash?

[@aldamaro5960]

Could the cceleration of space-time expansion by dark energy lead to velocity larger c? Or there is a limit?

[@ChristopherCurtis]

I think this is explained at 12:00 - the expansion is believed to be constant, not accelerating. So while the rate of expansion doesn't change, the distance between objects accelerates because new empty space increases the distance faster by adding its own expansion constant to the total space between the objects.

[@mgerye1]

We already see distant objects receding at greater than C. As the universe ages that horizon just gets closer and closer

[@Zoyx]

@@ChristopherCurtis - The Hubble constant isn't constant. It is increasing with time. That is another way the universe could end... the big rip. The expansion of the universe is so fast that the universe rips apart.

[@wayneyadams]

@@mgerye1 No we don't. Where did you get that idea?

[@BenjaminCronce]

@@Zoyx You're missing an "if". Currently, as far as we can tell, the Hubble Constant is constant, and thus its name.

[@smlanka4u]

Interesting. And roger penrose has a good explanation too.

[@frankkubrick865]

thanks Dr Don!

[@davidgreenwitch]

Do I get this right? Even at the tiny space between atoms dark energy is "creating space" and the atoms and molecules just attract each other "quicker" than they expand? Does that mean, we have to re-calculate gravity strength? After all it would be than a bit stronger than it appears, right? Maybe that changes calculations of dark matter estimations etc. After all there seem to be open questions regarding it's strength (extra dimensions, dark matter...) Could that explain something? Or is that idea nonesense?

[@cloudpoint0]

Dark energy doesn’t cause expansion, it just accelerates any pre-existing expansion. Dark energy’s effect is so weak that it takes 150 million light years of dark energy to get any measureable acceleration in the expansion of space. I don’t think there is any expansion within atoms or molecules to even accelerate. If there is it can be completely ignored. I don’t think there is any expansion within whole galaxies either. Galaxies are hundreds of thousands of light years across, not hundreds of millions.

[@davidgreenwitch]

@@cloudpoint0 sure the effect is minor. However that effect creates new space even on a small scale. So sure for molecules that can be neglected. However, if you sum that up on a scale of the milky way, maybe that neglectable value sums up to something bigger. Hence the question whether this might be an alternative idea for dark matter.

[@cloudpoint0]

​@@davidgreenwitch It doesn’t add up on the galactic scale because either it doesn’t even happen or it is negated by attractive gravity at the micro level, whichever understanding you prefer. Even if it did add up, a galaxy is just too small to have this tiny effect add up to a measurable amount. You need 1000 galaxies to maybe get the slightest measureable effect. Dark energy and dark matter are not at all related as far as we can tell. They just have similar names.

[@HoundDogMech]

Got a questions Why do the planets travel around the sun in a presumably flat plane and not in orbits as electrons around nucleus of an atom. as typically portrayed.

[@Ni999]

The solar system components started spinning as they fell in to the early blob. That continued while the blob started differentiating and so the whole thing had angular momentum as did the blobs that became planets, moons, and the sun. Over time that all turned into the disk we have in the center of the system. However, go out a little further to the Kupier belt and there's less smoothing, go out to the Oort cloud and it's all over the place. Our galaxy follows the same pattern. The quantum world is very chaotic. The model that looks like electrons have several nice orbits around the nucleus are just wrong. Electrons can appear in the nucleus and then out at some distance from it. Planets don't do that, we'd be dead. Why the macro world doesn't behave like the quantum world - and where is the line drawn between the two - are questions that we've been asking for over a century.

[@HoundDogMech]

@@Ni999 Thanks I googled it and they had Pictures made it all clear.

[@Ni999]

@@HoundDogMech 👍

[@Ni999]

@@HoundDogMech 👍

[@aamitcoh]

Hi Dr. Lincoln. As space-time "stretches" or expands, how do we explain the fact that its permeability to EM fields does not change? I would think that with "stretching" permeability should decrease, hence the speed of light increase. Thanks.

[@anniebooo]

Hi, can you make a video re. the concept around the convention of "the unmeasurable one-way speed of light" as presented in the recent Veritasium video? Thanks and best wishes, Annie

[@NeonsStyleHD]

How can you say the CMB is uniform when it looks so clumpy? I know the temperature variations are tiny, but it still looks clumpy.

[@drdon5205]

The earth is a sphere, until you look at it closely enough. Water is smooth, until you look at it at scales that reveal molecules. Glass is smooth until you use a very powerful microscope. The CMB is uniform to one part in ten thousand. It's not on smaller scales.

[@tobiasfox6882]

Hello, how do we know the "current" rate of the Universe's expansion, given that for objects further away, we are looking back further in time?

[@belshel4997]

Hi Dr. Lincoln, thank you for this amazing series. One of the things it made me reflect on is the question of death. How is death fit the basic law of energy conservation? That is, when someone dies, what happens to their life energy, where does it “go”? And would this law actually lean toward the existence of a soul, that may “encapsulate” such energy? I know this is a big “philosophical” question, but am curious to know how it's viewed from a purely physical perspective… Thanks

[@KasiusKlej]

When someone dies, most of his life energy goes to feed the worms, worms get plenty of calories. Then some of it goes to heat the air. Some of it goes to chemical reactions. And, depending on what you mean by life energy, some of it stays in bones for a long time. Soul is immaterial and therefore has no mass or energy, it exists as part of our universe though, or at least, since it's immaterial, somehow interacts with our world. The existence of soul should be evident not only to physicist, but everyone who can observe that there are creatures around with mind and soul.

[@belshel4997]

I'm interested in what may happen at the very moment of death regarding the physical energy level. Worms follow much later... Also, if you believe in the existence of a soul (which personally I'm uncertain about), then it probably would have some sort of energy, I believe.

[@KasiusKlej]

@@belshel4997 No, believe the physics, it wouldn't have any sort of energy. Soul is like a property. Man has a soul, I know it, I have seen men, and I have seen a creature without it, a beast, as well, so I know what a soul is. It is like a character, each man has a character. Or like a mind, everyone has his own mind. All this properties are immaterial. That is also why some say that soul is eternal, because it is not made of material, but that is incorrect, soul is quite mortal, I think, still, different people append different mythology to what a soul is.

[@belshel4997]

@@KasiusKlej Many people believe in many things, of course. However, I'd rather keep things strictly physical (rather than metaphisical). The "soul" is by no means the nucleus of my question, I mentioned it almost as a way of a metaphor, and at any rate only as a reflection of some energy form. Hopefully Dr. Lincoln will give us his educated answer.

[@XtReMz98]

Regarding dark energy and multiverse. You mentionned a possible lava lamp scenario for possible universes colliding. Could a universe collision explain both the energy require for the inflation model and, alike a lava bubble that got energy in the lamp expanding/rising to then cool off, explain why our universe is expanding?

[@richardajensen]

Can you do a video on the cosmological constant problem? Or at least give a summary of it & how you think it can/will be resolved?

[@cyberpersona6267]

Don, could phase transitions occur during the expansion of the universe and liberate energy to create new matter?

[@csabanagy8071]

I would very much interested what happening inside an atom when it is accelerating. As I see a movement of an object can only be interpreted in a frame of reference. A frame of reference are created by matter itself. If there is no reference the speed is meaning less... It means if we bombard space time section with high mass particle the frame of reference could be manipulated. See frame dragging. Could it work in microscopic scales if the energy concentration/mass is high enough?

[@Baigle1]

Can gravitational lensing by a large cluster moving at a high translational velocity be shown to accelerate, or shift the frequency of the light on the trailing side of the lens?

[@brianflaherty9054]

How does gravity increase entropy?

[@xxx56591]

Hi Dr Don ... if galaxy is not moving and is stretching with space then how can we say all superclusters will merge into The Great Attracter or Lanekia Supercluster... saw it in some other video

[@cloudpoint0]

Superclusters aren’t gravitationally bound so expansion of the universe should carry the galaxy clusters within them apart. The Great Attracter might slow this expansion locally a bit. I’m not sure if any visible galaxy is close enough to be pulled into whatever is at the heart of The Great Attracter faster than space is expanding, maybe a few are. Individual galaxy clusters are gravitationally bound so the galaxies within them should merge over very long times.

[@nimitagg95]

Could there be something outside the visible leading to the accelerated expansion of universe. Maybe like the gravity from non visible universe?

[@aarav_sharma]

I will put my bet on universe sized black hole...... but it is highly unlikely because the expansion is same in every direction and speed depends on the emptiness of the space also it cannot explain the ever increasing acceleration

[@gdmjolnir]

Is strange matter the optimal state of matter? Could a blob of strange matter keep from decaying into other particles if it were concentrated enough?

[@markrothenbuhler6232]

Are there currently any experiments that are attempting to "find" the graviton? If so, how likely are they to succeed?

[@alcash65]

Great explanation of flat space

[@rollinwithunclepete824]

Dr Don, I'm not your best student... but I really enjoy the class!

[@SinouA]

Hello Dr Lincoln, A question about dark energy in small volumes: I think I understand that dark energy is weaker than gravity to have a net impact in small volumes such as the solar system or even the galaxy. However, is there a way measure the gross expansionary impact of dark energy in small volumes?

[@nafeesaneelufer5023]

Hi Sir. Interesting video. If the objects at a distance more than 4285 megaparsecs move away from us with the speed greater than that of light, then the light coming from them will not reach us. Is this the reason behind why we can see only a part of universe i.e observable universe but not the entire one? If not so then why can't we see entire universe?

[@betaneptune]

Starting at 1:06 you talk about galaxies moving away from each other, but say that gravity might eventually pull them back into a Big Crunch. But later, starting at 7:24, you say the galaxies aren't moving, but space is expanding between them. If that's the case, then how can gravity make the space shrink so as to bring the galaxies back together (if dark energy were weak enough, of course)?

[@subhrajyotisaha3645]

Does expansion of the universe have effects like time dilation or lenth contraction between the receding objects.

[@iiropeltonen]

Question: As a particle physicist, do you Believe reality is deterministic and if so, do you Believe we as humans have free will as it requires our thoughts to be able to control particle interactions in the molecules that build our cells and bodies.

[@GreenJeepAdventures]

How many people does it take to run your average particle accelerator at Fermilab or CERN? How long to prep ?

[@drdon5205]

Thousands. Years.

[@joethestack3894]

Is there any difference between redshift caused by relative motion and redshift caused by the expansion of space-time?

[@florh]

another question about this "flat 3D space" that physicists mean. Why do they represent that with cubes and not tetrahedrons? It's also confusing when people like Dr. Neil DeGrasse Tyson and Dr. Michio Kaku explain how dimensions come to be. Their version tends to be: First you have a singularity, let's say a dot, because it has no dimensions, then when you add a dot and draw a line, you get 1 dimension draw 2 more dots and connect them again and you have a square, which is 2 dimensions draw 4 more dots and connect those again and you have a cube, which is 3 dimensions. Why do they have to "simplify" that, so that kids know what they are talking about? (i'm just assuming now) Why not, in levels of freedom? First you have a singularity, let's represent that with a dot, because it has no dimensions Add a dot, draw a line between them and you have 1 dimension or a line. (can be a curved line too for all I care, maybe at that point it's close to a black hole???) add one more dot and connect them with lines, and you have a triangle or a 2 dimensional thing add one more dot, and connect all the dots again, and you have a tetrahedron or a 3 dimensional thing Isn't that a bit easier to explain, in their version of dimensions, people will get confused because they will think that if we want to go to 4 dimensions, that they have to draw at least 8 more dots, while in my explaination it's still just one more dot. My dots actually represent those levels of freedom. I also doubt this one more dot is time, otherwise why the hell are physicists talking about spacetime if there is an actual separate dimension of time??? For me, before the big bang, spacetime was already there.

[@andrei-un3yr]

thanks Don, now I have existential crisis in the morning as well

[@theultrapixel]

How on-the-table still is the idea of a cyclic universe, with big crunch followed by big bounce and so on forever? Does inflation appear in any way similar to the big bounce which followed the previous crunch as far as our current low-energy theories can tell?

[@mysteryhombre81]

Hey Doc you say the universe will end a cold empty death but what do you think about Sir Roger Penroses Conformal Cyclic Cosmology theory?

[@cloudpoint0]

Penrose just says a new universe will arise to replace the cold empty dead one. The cause of death of the old one is still roughly the same.

[@mysteryhombre81]

@@cloudpoint0 Well not entirely, he claims that all matter will end and only thing that will exist is light, pure energy with no masss. Which then, for lack of better wording, can reach and breakthrough the infinity of our current aeon.

[@cloudpoint0]

​@@mysteryhombre81 Cold and empty includes a thin veil of low energy photons flying around just like in the non-Penrose understanding of the end. Where would all the photons go otherwise? They can’t decay and nothing exists to absorb them. Whether the photons breakthrough or not doesn’t change the cause of death of the current aeon. It just says something about what contributed to the next aeon.

[@mysteryhombre81]

@@cloudpoint0 Well when he said dark and cold, I kinda assumed he ment dark, as in no light, and cold, as in no energy, a vast infinite eternal nothingness. But maybe he didn't..

[@cloudpoint0]

@@mysteryhombre81 I suspect dark means no visible light, just very low energy photons that have been stretched into extreme redshifts. Low energy and extreme redshifts means cold. Imagine just one photon warming each cubic parsec of space. The ultimate chill. So one step removed from a vast infinite eternal nothingness if you wish. I'm not sure when the next aeon kicks off in this scenario.

[@Dennis-vh8tz]

It would probably be more accurate to say that the _visible_ universe expands at the speed of light. If the entirety of the universe (both visible and non visible) is infinite and physics are consistent throughout, then it must expand at infinite velocity as points with infinite distance (megaparsecs) between them will have an infinite separation velocity. If the non-visible universe is finite but has consistent physics throughout then, I believe, we currently lack sufficient information to determine it's size expansion rate. If physics differ between the visible and non-visible parts of the universe, or vary throughout the non-visible universe, then it would become even less likely we'll ever know the overall size or expansion rate of the universe.

[@zuban222]

Hi Don, what happens to the CMB? Will it be different for observers in galaxies and for observers in space? Does it go just fainter or the wavelength icreases to infinity?

[@drdon5205]

It's the same for everyone, although there is a tiny difference for each galaxy due to their motion WRT the CMB. Long term, it gets fainter and the wavelength gets longer.

[@AtonyB]

What 'traction' does the expansion of space have on matter? For example, if you were somehow to attach a rope between two objects diverging because of the expansion of space, what tension (as a function of distance and mass) would you expect the rope to be under? Is it the Higgs field coupling the masses to expanding spacetime, or are they simply following geodesics and the force in the rope is actually accelerating the masses to keep them at a relative distance?

[@shlokthakkar9189]

Sir u are the best

[@merwynraj8660]

How much important are physical constants? Is it true that all the constants are fine turned for the universe to exist as we see?

[@4draven418]

Hi, Dr. Lincoln, always enjoy your videos. Just a thought. Does/would entropy assist DE in the eventual equilibrium of the universe or would disorder create a situation of an increased chance of galaxy collisions. I haven't thought this through so I wonder if it is as contradictory as it sounds.

[@shravankrish]

How do we know that the bending of space time is not the effect of gravity rather than the cause? Also, what prevents new space from being created near large objects? (For instance, within a galaxy or even within the solar system.) Bent space doesn’t stretch?

[@filomenaa]

At these distances gravitational interactions are strong enough to counteract any effect dark energy has. It is only over large distances that gravity becomes weak enough that dark energy can overwhelm it.

[@shravankrish]

@@filomenaa But gravity is caused by the bending of spacetime. So, there should be something special about distorted space?

[@Bassotronics]

Before the Big Bang, nothing is everything!

[@pawelkrol6547]

I really like the fact that you focused your talk on the most likely prediction for the end of universe. I get totally bored watching videos discussing all those other alternatives (like big crunch for instance) that were now ruled out in favour of the explanation you presented.

[@tsraikage]

we have grand unified force that branches as energy decrease. are we sure that our four known forces stay the same even on the smallest energies? or are they still branching out to infinitely many different forces as energy goes to zero? if not, why?

[@champisthebunny6003]

Could we get spoiler tags for this one please?

[@cstasila]

How is the constant repulsive energy density of Dark Energy different than a universe that is slightly curved? Specifically, what observations have been made to state that it is Dark Energy that is causing the acceleration of the expansion of the universe and not spacetime curvature itself?

[@louislesch3878]

Electrons: *Particles or Waves?* Someone asked a question on Sabine's video presentation of pilot wave theory a couple weeks ago basically what is the use of particles when you have QFT. I had responded saying that I had thought it was because when you run the double slit experiment on individual electrons you get a definite ping on the screen as opposed to a smooth probability distribution of the interference pattern of a wave like you see with a single photon. This went down a whole rabbit hole that I don't know if it was ever actually answered. Dr Lincoln, can you please explain how individual electrons run through a double slit experiment show up as definite pings that when accumulated over a bunch of them show the well known probability distribution of the double slit experiment?

[@samuelrodrigues2939]

Hi Don if it is not known what is dark energy and even if it exists (did i get it right from previous videos) how come we can calculate its influence in places like vicinity of the Earth? (I recall that for distance galaxies it is light frequency shift, but how can it be traced back to like planets)

[@drdon5205]

We're pretty sure dark energy exists. We're just not sure what it is.

[@blinkin304]

i have 2 questions: 1) since Andromeda and the Milky Way are on a collision course does Andromeda appear blue shifted in our telescopes on Earth? if red shift is caused largely by expansion of space, then reducing the amount of space enough to overcome this expansion should cause blue shift since there is less space to expand between the two objects. 2) if motion is all relative, then why is change in motion (acceleration) not relative? if you are in a rocket going a constant speed then you can claim that you are stationary and that the universe or some other object is just going that speed in the opposite direction relative to you, but if the rocket is accelerating then you can't claim that external objects are just accelerating in an opposite direction, because you can feel the effects of acceleration directly.

[@michaelsommers2356]

Yes, Andromeda is blue-shifted. Red shift is not only caused by the expansion of the universe, but also by ordinary motion away from the observer, and by gravity.

[@blinkin304]

@@michaelsommers2356 that is why i added the word "largely" as a qualifier, but good to know.

[@cloudpoint0]

The Andromeda Galaxy is moving toward our own Milky Way galaxy within the Local Group; thus, when observed from Earth, its light is undergoing a blueshift. Wikipedia. Constant velocity is straight line motion - no experiment will discern which of two parties is truly in motion. Acceleration is curved line motion. The pseudo forces generated going around a curve affect just the party who is accelerating. The other party’s perspective is not relevant. In General Relativity, confusing though it is at first, you are not accelerating if you jump out of a window, but you are accelerating if you stand on the Earth.

[@blinkin304]

@@cloudpoint0 doesn't that imply that space-time is a medium that resists change itself and that reference frames are distinguished by the energy required to reach them? even in "flat space" outside of a gravity field you should still be able to feel the effects if you were accelerating in a rocket ship. in that case there would be only straight movement along a "flat" plane, the movement would just be increasing.

[@cloudpoint0]

@@blinkin304 Even if you straight line accelerate in flat space, you are traveling in a curve in spacetime. Your ratio of spatial axis travel is increasing vs the time axis. Spacetime is not a medium, it is a geometry.

[@kevinhanley3023]

As the distance between objects expands, is the there an acceleration?

[@nileshgaidhani6820]

Hello Sir How gravity will be dominant over expansion in due course of time although F=1/r^2?

[@thedeemon]

It won't be the newtonian gravity of massive bodies, it will be the (anti-)gravitational effect of the dark energy pushing galaxies apart.

[@michaelnorthrop1205]

What's the state of entropy in a heat death? Would that represent 'maximum' entropy or would quantum fluctuations still create some sort of entropic gradient? In such a state does time still flow or is there even a concept of time?

[@thedeemon]

Max entropy, no gradient, and pretty meaningless notion of time.

[@ChristopherCurtis]

Thank you for taking the time to do these videos. Given that space is rigid and space is flat, and that the arc we see drawn by a thrown basketball is it travelling in a straight line through (predominantly) a curvature in time, is there any relation between "dark energy" and time? Could it be that the expansion constant is the rate at which time is added to space, and that if the universe were to shrink time would run backwards? On a separate note, I wonder if some quantum uncertainties could be related to these systems "stealing" energy from the expansion in order to prevent themselves from succumbing to it (or, maintaining gravity).

[@dominiquejeangille9254]

Hi Don, I am still puzzle with the expansion and the speed of Light. Is Light going faster in an expanded universe or is it an absolute absolute constant ?

[@jimkennedy4509]

Question: in black holes it is said that it has a singularity. What if there is a limit to density of matter? Like a neutron star is very dense what if there is another maximum density where matter cannot be compressed further? How do we know this is not true? (Not proving that false does not make it true)

[@eniocs1428]

Hi Dr. Lincoln! If space is expanding, it means its getting bigger, right? If its getting bigger, does that mean more virtual particles are being created? Could the anhilation of virtual particles be the driving force of the expansion of the universe? Or am I just tripping?

[@cloudpoint0]

Virtual particles don’t physically exist as objects. They are more of a construct used to express the idea that a quantum field can be momentarily affected by what is happening (e.g. the jitter) in the other fields around the first field, or perhaps happening elsewhere in the same field. Virtual particles represent the presence of some kind of non-particle disturbance within the first field. The disturbances don’t annihilate either, they just die away. If you created a pair of virtual particles traveling in opposite directions, why would they ever turn around and annihilate again? They won’t. Each quantum field is just a seething mess of disturbances. In a way it is correct to say each real particle is partly made of many virtual particles. There also virtual particles which show up as internal states of Feynman diagrams - these don’t have any reality, they are just mathematical things. profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/