23 Subatomic Stories: Dark energy and the fate of the universe
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- čas přidán 22. 05. 2024
- Mysteries abound in the universe, including the universe’s ultimate fate. In this episode of Subatomic Stories, Fermilab’s Dr. Don Lincoln talks about the observation of a new form of energy called dark energy, which will determine the future of the cosmos.
Register for Don Lincoln’s public lecture:
events.fnal.gov/arts-lecture-...
Fermilab physics 101:
www.fnal.gov/pub/science/part...
Fermilab home page:
fnal.gov
Berkeley Campus image:
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The equation he displayed at 4:25 deserves a comment. Too often it is displayed, named, and glossed over without emphasizing its beauty and simplicity.
The term on the left, G is the Einstein Curvature Tensor, in simple terms, it describes the shape of Spacetime. The term on the right is the Stress-Energy Tensor which in simple terms is a description of the distribution of matter and energy the source of gravitational fields.
Do you need to understand all that to appreciate the beauty of this equation? The answer is no. What you need to take away from the equation is that Einstein showed that energy and matter determine the shape (curvature) of spacetime while the shape of spacetime controls the motion of matter within it.
The simplicity is mind boggling. Imagine, he was able to set one tensor equal to the other with nothing more than a constant multiplier It bears repeating, a set of equations (the G tensor) for the shape of spacetime are equal to a set of equations (the T tensor) describing the distribution of matter and energy.
There is one more term, the Cosmological Constant which was needed to explain the expansion of the universe, but the entire equation is still the best model we have for the universe.
Even the constant is amazing, The terms are pi, The gravitational constant G, and the speed of light C.
Obviously the terms in the tensors are not simple to determine, however the simplicity comes from the fact that it is possible to equate two unrelated tensors using nothing more than a constant multiplier.
If this were Einstein's only contribution to Physics it would be phenomenal and evidence of his genius. A fact too many non-scientists fail to appreciate as they post comments about how they have proven Einstein wrong, and how he did not know what he was talking about.
Wayne Y. Adams
B.S. Chemistry (ACS Certified)
M.S. Physics
R&D Chemist (9 yrs)
Physics Instructor (33 yrs)
This chanell is my favorite even tho I understand only 2,057% of what the proffessor is talking about. I just like to listen to these kind of videos before sleep. 10/10 would listen again.
THANK YOU PROFESSOR LINCOLN...!!!
12:50 this is the kind of insight I love from this channel. Thank you so much Dr. Lincoln
8:56 beautiful. This is something so many people dont understand these days.
Some think that scientists think they know everything. This might be the case for some, but in general I believe many scientists admit that science is progressive in nature and you cannot know everything, ever.
dick prickenson I think it’s definitely more nuanced than that. The frontier of science is very changing, yes. But that’s because there’s so little experimental data one way or the other than new data often creates complications. But for everything older and with more evidence, I believe it’s more apt to say that science refines rather than changes. Science has made too much innovation and technology to disregard it as changing all the time. So much of the core stuff stays the same. Like Newtonian mechanics being just fine for like 95% of applications
@dick prickenson Wrong. Science is a method which when practiced perfectly helps to counteract our innate biases iteratively narrowing down possibilities to asymptotically approach the "truth". The notion of truth is unscientific in the same sense that infinity is not a number but while wcertainty
Any good scientist knows that we can't ever truly know everything for it is beyond the scope of knowledge and that no belief will ever become completely true but we can help make better informed beliefs since people unfortunately are wired to have beliefs.
dick prickenson yeah of course Newtonian mechanics are wrong. Also 95% was a number I pulled out of thin air to express my opinions. What I meant by it was that the vast majority (in my very rough estimate 95%) of the time physics is being used in the current year, 2020, Newtonian mechanics is accurate enough for the applications. Obviously most applications things relating to space aren’t well served by Newtonian mechanics but since in the current year 2020, space related science makes up a small percentage of all uses of physics, 95% feels accurate. Building roads, houses buildings, measuring tensions and stresses and fluid dynamics, almost all of civil engineering can be done with Newtonian mechanics alone.
Dragrath1 I really like the phrasing of this comment, especially the “asymptotically approach the truth” bit. I’ve just thought of it as a refining process, but this much better explains how I had it picture in my head. Thank you.
Thanks again and again Fermilab.
Great physics series...
I’m a high school physics teacher and I enjoy your videos which often go well beyond the curriculum of high school, or college, physics. Thanks! I am wondering where you get your cool t-shirts and wish we could see more of the shirt’s messages than you typically reveal.
I am going through the playlist, amazing. Thank you so much, Don! I keep starring at the books behind you, and I have an idea for you. It would be great if you could show one book in every video, just for a minute-a ninja review.
Take care and stay safe!
Thank you once again sir.
What kind of schmuck gives this series a thumbs down? These videos are great and Dr. Lincoln has to be one of the most friendly and likable personalities on the Tube. I guess there are people who are just mad at the world - these are the types that deliberately pee all over the toilet seat in a public restroom.
this is one of best sub atomic stories so far, gravity explain was too
Can't wait for the recording of your talk to come out!
Just gotta love your patience and good humour in dealing with those "luminiferous aether" folks... 😁👍
Probably been sniffing the stuff ;) Actually no, hold on, in THIS context it's a fair question..
Just like 'The Ether' was a placeholder for something we figured must exist, so is 'dark matter' and 'dark energy' , right ?
I think what the questioner means, the data may be telling us we need a new model of things, just like when Relativity came along. So far I think we've failed to detect or interact with Dark matter or Energy in ANY meaningful way? We know something LIKE it must exist or .. Or we looking at things wrong.. Again ?
PS If youre referring to SOME of the people you get on here (of whom I think the questioner *isn't*) - i was in this early dotcom, and we all thought having the worlds knowledge at your fingertips would make people SO smart - what we HADNT figured on, is we'd simply be mega-amplifying the human tendency to tell tales that are only 'true' over a limited domain (flat Earth, racial superiority..) just to sound good - just like politicians have done for centuries
Dark matter galaxies!?? Cool! Great video as always Dr. Don.
Loved the q&a. How about some q&a only episodes?
Hey Don, assuming that gravity is not a force, and only a distortion in space-time, is it possible that the strong, weak and EM force are also not forces and just some phenomenon that we have not yet thought / discovered?
Particle physicists don’t really accept the notion of forces. They talk in terms of interactions instead (where cause and effect are unclear).
Since physics is everything, if someone clicks the dislike button on a physics video, then clearly that person dislikes everything.
Hi, Don. Love your videos! I have a question about neutrinos:
If I'm undestanding it correctly, as long as you didn't measure the flavour of a neutrino, it's in a superposition of all three flavours. This superposition has a probability distribution of what flavour it's most likely to be. The longer the distance (or time?) has passed after it's creation, this probability distribution changes, because there was more time for the oscillations. Do neutrinos eventually converge to the same probability distribution of each flavour, independent of which flavour it originally had?
A big thank you to doctor Lincoln and his team at fermilab. I only discovered these short videos this week, luckily i have been on night shift and have manged to watch and like all. i have of course become a subscriber. I have a question, which maybe dumb. is it possible that as well as the forces we know there exist others, for example a force like an inverse strong force which becomes very strong when things are far apart, and could this explain the structure and expansion of the universe as observed. thanks.
Awesome
Had to listen twice to make sure I followed it all.
Now I can't stop thinking 'dark energy' is actually a feature of space-time. In my mind's eye I now see space-time as gently convex rather than the flat grid that is usually presented. Greater distances between objects puts them at increasingly steeper 'angles' of space-time from each other, each 'falling' and accelerating toward a different edge, as a group of marbles would if placed on top of a large smooth sphere.
Years ago in school I was warned about "modelitis," making predictions based on models known to be imperfect. Still, this mental image has a feeling of rightness to me.
I can't believe that 23 weeks have already passed since the start of the pandemics. Time truly flies fast, especially with such interesting videos. Keep up the good work!
How you feeling about the time now 😂😂
"Thank you for your Ticket Purchase." Thank You!🙂🙂🙂👍👍
Hello, first, congrats, great channel!
Sir, I know you said a bit of it in past videos, but would you mind to make a video explaining (mor or less) the path to become a physicist (teorical and praticle) considering the academy + research centers?
Thank you.
Hi Dr. Lincoln love your series. I was wondering could you talk a bit about gravitons? I’d like to understand a little bit about their different vibrational modes but I’m not sure if that’s in the realm of string theory
I keep watching videos about dark matter and dark energy. I get it that the competent scientists may not know what either really is. But I haven't seen a presentation on what options are being considered or even speculated about. I would like to learn some of these to move forward in my knowledge. Thank you.
Maybe a good starting place for you would be…
backreaction.blogspot.com/2020/03/are-dark-energy-and-dark-matter.html
Also follow the links within the article or check out some of the following.
czcams.com/users/results?search_query=dark+matter+and+energy+sabine+Hossenfelder
John Clarke Options for dark matter were discussed in the last 2 videos.
CZcams is filled with such content, but it may be helpful to move past popular science videos and into academic lectures.
I would very much appreciate an episode that explains why the red shift that's attributed partially to the big bang and partially to dark energy can't be explained instead by an alternative theory. For example, "tired light" was once considered as an alternative. Another alternative that comes to mind is that the Earth is actually at a special place in the universe such that light must travel "uphill" to reach us. No doubt physicists have reasons to believe all alternatives have been disproved, and it would be great to hear those reasons and the assumptions those reasons depend on.
Great video as always Dr. Don! I'm not sure that I understood the part of the video stating that galaxies had been found without any Dark Matter? How is that possible when we don't even know if DM even exist? Very confusing but thought provoking none the less!
We don’t know what DM is but we have direct observation of effects that can’t be explained with conventional physics. The effects are there, something must be causing them. Scientists call that something dark matter.
One of the effects is a difference in the rotation velocity of galaxies. In short astronomers find that galaxies move faster than the amount of stars in them makes possible, so there must be an invisible amount of matter that pulls galaxies together and avoid stars flying off. They presume that invisible matter is “dark matter” and by measuring luminosity and velocity and plugging the numbers in the equations they can estimate the quantity of dark matter each galaxy contains.
Nice
Since we know about particle/wave duality, why are gravitational waves not enough evidence that gravitons exist? Are there models that are reasonable that allow for gravity to not be quantizeds?
Good as always Dr. Lincoln, my understanding rate it's about 85 percent, but I improve my English, so, I have a.... hope...,greetings from the land of Democritos.
Thanks a lot for this great video. I had a question for you as to what should I pick up Nanotechnology or Astrophysics. Well, I am not highly interested in engineering and am trying to avoid it. I have an aim for joining ISRO and have quite a lot of passion regarding both nanotechnology as well as astrophysics. SO which career would you recommend taking into account the popularity and need of these occupations and which one you find more interesting.
Abhiram Vartak you should base your choice on what YOU find interesting, not somebody else. If you hope to join ISRO why don’t you ask them directly which career path is more likely to get you there?
To solve the paradox of the accelerating galaxies, the theory of gravity need to be changed to be attractive in short distances but repulsive in long distances.
For example, for distances more than 2 billion light years, gravity will be repulsive. The further away, the stronger the repulsive force.
One emerging result of surveys of late has been that in the nearby universe things seem to no longer be isotropic out to a further degree than expected. I wonder what effects that might have if it holds up?
Also on note for the whole notion that dwarf galaxies have higher amounts of dark matter than larger galaxies it should be noted that the Large Magellanic Cloud galaxy has been found to actually be massive enough to have its own retinue of satellite galaxies as well as a substantial gas halo. The recent results seem to have finally solved the question for why the Magellanic stream is so massive revealing it is likely the product of the ongoing collision between the hot baryonic gas within the Magellanic Cloud halo into the Milky Way's own baryonic halo component. Thus far this shock front has protected the Magellanic clouds own gas supply from the pull of the Milky Way but it will not last forever.
Great Videos. Thank you. Question, I read that there are galaxies that don't have dark matter at all. In the galaxies that have dark matter is it evenly distributed? If not, why? Is there a preference for dark matter to lump around something?
Recent studies suggest the universe isnt expanding uniformly in every direction. Is it possible that some event in our observable universe caused it to slow down, then expand rapidly as you described, whereas outside out observable universe, it isnt expanding in the same way?
hi Doc Lincoln. how do we measure the time since the big bang if the expansion is near to the speed of light. is the time still linear ?
Expansion doesn’t have a speed. It has something that’s more or less a doubling rate. Or “a speed-per-unit-distance, which is equivalent to a frequency, or an inverse time”, in the more precise terminology used at the first link below.
medium.com/starts-with-a-bang/ask-ethan-how-does-the-fabric-of-spacetime-expand-faster-than-the-speed-of-light-f8a484738ee
This might answer your main question.
medium.com/starts-with-a-bang/ask-ethan-99-how-do-we-know-the-age-of-the-universe-64c07c83a80
The expansion can be faster than light. Galaxies further than about 9 billion light years away (look back time, or at redshifts above z=1.4) are travelling faster than light away from us in a very unintuitive way. We can see their light, since it was emitted towards us at over 5 billion years after the big bang, but the actual galaxy (and everything else beyond that distance such as the cosmic microwave background) is moving away from us faster than light (up to about 3 times the speed of light at the observable horizon, and up to 45 billion light years away) and is now at least 14 billion light years away (proper distance). These distances and times are calculated from cosmology equations such as the Friedmann equations which are derived from general relativity.
there is this concept called conformal time which simplify things. you should look it up on the internet.
thank a bunch folks. I started this quantum stuff with no understanding at all. now I am in the confused stage. I will start 2 read them.
Are there any estimates on the total gravitational wave energy traveling through the universe? Is this figure taken into account when considering the total energy/mass the universe is ought to have.
I have heard about this topic many time, but it is certainly the clearer explanation I have seen.
Just one question: in 1915, Einstein was 36 years old (and 26 years old in 1905). Why do we always see pictures of Einstein much older to illustrate his discoveries ???
Probably because he became a celebrity later on in life. He only got a nobel prize in the 20s for explaining the photoelectric effect.
Hello Don! There was a paper published by Jacques Colin et al., Evidence for anisotropy of cosmic acceleration, Astronomy & Astrophysics (2019). Their analysis showed that the observed acceleration of the galaxies is a result of local movements and it's not isotropic. It could do away with the existence of dark energy. Do you have any thoughts on the matter?
I googled that paper. An article this year in Wired, available online, discusses that research and most cosmologists apparently believe the analysis is flawed and that dark energy is still the best theory.
Don, I ordered a Zoom link for your lecture this evening. Looking forward to it! Will the centerstageticketing people email me the zoom link?
Never mind. Got an email. Cool!
Hi Don! Great video as always! Do you have any other good historical examples of when scientists performed an experiment that resulted with their own 'Option 4' like what happened with the expansion of the universe?
Michelson & Morley? Hubble's expanding universe?
Trying to register for you webinar it would be nice to understand what timezone 7:30 pm refers to.
Chicago. US Central time.
Dr. Lincoln, (9:55) Go Bears! UC Berkeley Unfortunately the photo is of the library and which is blocking the view of the Physics building where the first artificial element was created? Any ideas what element that was?
Another wonderful video.
I think Dr. Don's career plan B was to be a stand-up comic, check out his fantastic delivery with this answer: 9:05. Plan B would have worked pretty good I think.
Next he'll answer a question like "Why did the Big Bang happen?" with "Wasn't me!" 😂😂
Thank you for the videos.
If matter and energy distort space and time could that Distortion be compressing space? If it is, that reasons that about 5 billion years ago the Galaxy started getting far enough away that space was expanding back to its previous state and size. Is there enough space expanding fast enough to both compensate for the Galaxy slowing down and our perceived measurement of them speeding up?
Hi Doc.
We are in toroidal universe and we keep going around the hamster wheel?
interestingly, gravity also plays a certain role in making stars shine
And in making moonshine.
Not to mention novas, super novas and hyper novas.
Hey sir , warm regards from my side , I want to ask that the dark matter concept which was introduced for the missing mass can be solved by the relativistic mass of the universe if it is moving , we can use Einstein's formula of M=E/C² , if we are able to calculate the velocity of the universe then we could find its relativistic mass and if it fits to our calculations then there would be no scope for dark matter
I have a serious question. Maybe I'm naive so if we look at the universe and see that it has slowed down and then has begun to expand again have these calculations included the effect of gravity on time and our position as an observer, wouldn't it make sense to view the universe as the other side of a blackhole? As an observer moving away from the singularity and looking at objects farther away would those objects look the way they do now? After all a singularity has infinite density so its effect would be infinite within the event horizon but would begin to resemble normal space the farther away you get. information can't be destroyed but there isn't any reason to think it couldn't be transmitted to another (in this case) universe. I love your channel btw. Keep it coming.
I think dark energy is the shadow of a previous universe. I mean to say I think its linked to hawking radiation. but from the other side of the singularity
Hello, Dr. Lincoln!
Is there any chance that dark matter is the result of some weird interactions between neutrino-like particles (or neutrinos themselves) and the Higgs field? Or are we just better off looking for sources of mass different from Higgs field and particles beyond the standard model in this case?
When using redshift to work out the radial velocity of very distant objects, how do we separate out the doppler shift from relative motion, the gravitational redshift, and the cosmological redshift from the expansion of space itself?
There are methods have no idea what they are tho
It has been written in all my studies that a particle like a photon transmits electromagnetic force, but it has never been said how this force transmits or receives this force.
This is very important to me, please answer!
Sadly I can't make the lecture but I will definitely be keeping an eye out for it being posted on CZcams!
Look at my channel
Hi, while reading your interesting book 'Understanding the universe', I realize that we, our solar system, is emitting gravitons or gwaves that will never reach areas that are now abandon our visible universe. ¿What happen with the gravitational field we created when those areas were nearer? ¿Will the field we created in those areas stay or will it fade? (sorry about my English)
What if space isn't expanding, but instead all fermions are shrinking? We wouldn't be able to tell the difference, because leptons and bosons are point-like anyway.
How do you even build a giant circle like a partical accelerator ?
Is it almost perfectly round ? does it need to be ? what methods are used to make sure ?
really big compass. I've always wondered how they made the first rulers.
Just an idea is that there may be a positive curvature to gravity where there is none as to push things apart, or be anti-gravity. You are not supposed to be able to accelerate anything FTL, so if this is observed you can also argue the fabric is expanding FTL, but gravitational waves are not doing that. So it is odd.
A question: does entanglement hints at hidden/additionals dimensions? Maybe we distance the twin particles in the usual 3 but they remains linked in some additional one/s. If not, what is the mainstream explanation for it?
In Germany, we also say "oops" ("ups") 😃
Not surprising. Tons of overlap between German and English
@@MuttFitness
Also that some 50% (maybe 60) of us white americans have German ancestors
I would translate it with "Hoppla".
Could have done with more umlauts, though. :P
@@oisnowy5368
Umm louts ??
Imagine I have a huge flat bedsheet. Then I grab a small area of it, and I pull it together into my fist as tight knot. Now imagine that this “knot” is the particle, and the stretched sheet around it is the warped space time.
Is it possible that space-time relates to matter just like that? Can the particles be just “clots” of spacetime, and curved spacetime would be just the stretched regions around these clots?
what;s different from string theory on you're assumptions?
Out Smoked In string theory, strings are things in spacetime.
What I say is that spacetime itself is curled up to form particles (strings whatever).
is dark engery considered bending the space in the opposite direction as energy and matter do or how does it work?
Hi Don.. can u extract and use dark energy for something?
Hello doc, can you please give a bit more clarity on how dark energy came to be? I first heard about how it doesn't follow law of conservation of energy when I was watching videos on Noethers Theorem. I kind of understood how red shifting of EM radiation is an example of when law of conservation of energy isn't obeyed but I didn't quite understand dark energy.
dark energy it's not electricity it's more an unexplained phenomenon, all galaxies getting/adding lots of space between them at accelerated rate
The more distant galaxies also emitted the light we are observing earlier. If you graph the time at which it was emitted by the redshift, wouldn't you instead conclude that earlier in history, there was more redshift? Thus the universe would be decelerating over time. What makes us think that the redshift now is reflecting the current recession rate and not the rate when it was emitted?
Sir do space time have an structure I mean to say like cloth has Internal electromagnetic forces that is the cause of electromagnetic potential energy and due to Which if there is any distortion in the cloth there is an storage of electromagnetic potential energy
Like this space do have potential energy due to which it can distort and reshape but which force is responsible for the structure of space time ?
The answer is almost certainly a yes. However, we don't quite know what the nature of this internal structure is. Or rather, we have several good ideas, none of which can currently be tested. The one I think is most similar to what you describe is that entanglement is what keeps spacetime together. Check out Leonard Susskind's 2 part lecture on this, he called it "ER = EPR", if you want to know more about that.
I understand that they discovered that the universe is expanding faster now. But I'm a little surprised by the fact that they are convinced that it was slowing down until few billion years ago. How can the scientists conclude that?
Would a sufficiently 'less expanding' big bang, if that make sense, have led to a big crunch before Dark Energy took over?
Also, I hope a future episode on Inflation is coming :-).
Hi Dr. Don. You mention that the universe as a whole will collapse, hold steady or expand forever. However is it possible that there are local regions of the universe that would have different fates from each other. For example could there be a region of the universe that has a local Big Crunch, another that holds steady and another that expands forever?
Great video as usual! But... Isn't the correct singular "phenomenon" rather than "phenomena"?
Hi Don. Great video. Do dark matter and dark energy give a solution to the singularity problem inside a black hole?
Not yet, perhaps not at all. There is always the outside chance that an understanding of either or both could give us a theory of quantum gravity, but so far it doesn't look that way.
@@ozzymandius666 isn't it better then to work on a modified theory of gravity? The search for dark matter and dark energy feels simular to the search for the planet Vulcan when newtonian physics couldn't explain Mercury's orbit.
@@dannyb2816 Not really. Dark matter also causes gravitational lensing, as if it were Einsteinian mass between us and the galaxies that emitted it, but only in very few directions. How would you explain the rare lensing effects, and the much more common lack of lensing, for objects at the same distance? Some "special directions" for gravity?
If you calculate the mass of the fluctuations of the vacuum would that time average be similar to the mass of dark matter expected? Also would the entropy of those fluctuations look anywhere near that of dark energy?
Question. Since the existence of a real event horizon would create a lot of troubles for information and whatnot, couldn't it be that the gravitational collapse stops at something like Schwarzschild radious+ plank lenght? I mean would there it be any way of experimentally verify that the horizon we are (not) seeing from the event horizont telescopes is a real event horizon and not just a very, very dark surface?
How robust is the observation that the expansion of the universe is accelerating? I heard there have been some recent reanalyses of the data that question the measurement. Also, if a small fraction of the light from distant galaxies gets absorbed on its way to us roughly uniformly, but through a mechanism we're not familiar with (rare interactions with dark matter, perhaps?) couldn't that reduce the brightness of the standard candles and make them appear more distant than they actually are, thus increasing the observed acceleration?
Cool
Hi Sir
Your talk is scientific as always
I have one doubt
If dark energy is responsible for expansion of the universe and galaxies are moving away fast then why not planets move away from each other or two stars in a galaxy. Does it mean that dark energy is not present within the galaxy? Or if it is present here, gravity overpowers it within the galaxy? Or is it the dark matter that holds on the galaxy structures as they are and seems to overcome the dark energy? Please reply, thank you
FYI, the public lecture doesn't specify the time zone. Is the talk at 7:30p CDT? Please specify!
7:30 Chicago time.
Any thoughts on the theory of everything that says the universe is a neural network?
do you take into account the movement of objects between us and the source that moved into and then out of the field of view during the transit the light took to get to us? example, we look at a star 10 billion light years away, a massive object 5 billion years ago entered from the left of our view to the right in a matter of a few billion years. object is now (to us) on the right of our field of view (looking at same star from the start)
so could, black holes, pulsars, quasars, and such effect the spacetime we see now making us think its dark matter/energy?
I think the first time I heard of conservation of energy being broken was about light red-shifting and losing energy. If dark energy is a property of empty space gaining the energy density necessary of a vacuum, could it be that it takes that energy from the light that loses it as it crosses through that space?
Hi Don.. can dark matter (or matter) absorb dark energy? What happens when they meet?
@7:15 but what is the reason for concluding dark matter exists, rather than concluding that our assumptions about how regular, detectable matter distorts space-time might be wrong or incomplete?
Would it be difficult to make a computer model just using Einstein's
general relatively to show impeding gravity from other sources attributing to the slow down of expansion?
I wonder why Dark Energy is called just that, and not Dark Force or Dark Power. Every description I have heard of it, including this one, seems to indicate that it is a phenomenon where energy is added to the universe in some sense.
Cause Luke can't use it
Great vid. If Dark Energy is increasing, is it possible for it to slow in the future?
Since the evidence is consistent with a constant energy density throughout the universe, it suggests that it won't change. However, since we still don't understand what causes the change in the expansion rate, any such deductions are very tentative.
@@MusicalRaichu Generally the assumption that dark energy is constant through out the universe is directly tied to the assumption of an isotropic universe which is well supported by the Cosmic Microwave Background and observations of the distant universe however there has been a growing body of evidence that the local universe is significantly anisotropic which seems to occur around the time frame where the acceleration associated with dark energy picks up. It is still fairly controversial but if it turns out to be correct dark energy might not be entirely uniform or perhaps there is some additional frame dependent effects to account for?
Dear Don,
If Univers is expanding and we assume that there is no absolute vacuum, what fills the space preventing it from breaking ? matter ? then gravity increase, isn't it?
Xavixavi
As a follow up to one of the questions (dark matter in Milky Way): why can't we measure amount/distribution of the dark matter surrounding the Earth by measuring how a gravitational pull of our planet changes with the distance? If there is a dark matter then since it has some mass, we should be registering bigger pull than in the case there is no dark matter there.
The dark matter in the solar system makes up the equivalence of one asteroid. It's so tiny that it is beyond our measuring capabilities.
Dr Don Lincoln Qu: I read that gravity can be restated as an acceleration towards slower time (feet aging slower than head). Is there a relationship between gravity and the time dilation experienced when accelerating?
@dick prickenson I will refine the question using your example and ask it again next week. Thanks for your answer.
hi Sir DON, apologies for second question in same episode
source: hubblesite
A recent study of 11 hefty galaxy clusters found that some small-scale clumps of dark matter are so concentrated that the lensing effects they produce are 10 times stronger than expected.
question:
dark matter is just, fundamental building blocks between energy and fundamental building blocks we know?
whats your opinion?
So far we have no idea that whether or not it would take a place in force carrier or something independent of all
5:30. Einstein is so genius that even when he blunders, he is still right. thats how far he is ahead of his time
Hi Don.. whats the interaction between a blackhole and dark energy? Do blackholes expand because of dark energy? Do they absorb dark energy?
Question: considering a black hole, why is singularity a consequence of event horizon ? Isn't it possible that there, under the event horizon, there's a gluon star, or other degraded matter object? But still having a size rather than a point.
Event horizon is a region where light is to slow to escape, it doesn't mean that everything underneath must be crushed to a point.
General rule of thumb for physics is that the numbers 0 and infinity aren't applicable, so singularities probably don't exist.
Does it make sense to talk about velocity and speed of galaxies when it is space itself that is expanding, rather than galaxies moving through space?
It makes sense because we cannot actually measure the motion of anything in relation to empty space-time itself but we must always have some other object to compare its motion with. Since we cannot measure it any other way it doesn't make sense to talk about it any other way either. And furthermore you can never in any particular single measurement tell how much of the measured velocity is due to the space expanding and how much is movement through space. We get the expansion rate as an average rate from alot of different measurements by making a couple of assumptions.
First assumption is that since far away galaxies presumably move through space in random directions their relative speed towards or away from us ,caused by their motion through space, should average out to about zero. So if you measure the relative speed of enough number of galaxies at some particular distance you should get an idea about how fast space itself expands since. The other assumption is that distant galaxies moves through space with the same kind of speeds as those close by do, which we sort of can measure with a bit more confidence. That speed is the relatively slow, 'only' a few hundred miles per second or so, which is why the much faster speeds away from us by the really distant galaxies requires an explanation.
I had a question about gravity which your mention of GR reminded me of: If we can now detect gravitational waves, why can we not find the supposed force carrier (graviton?) that these gravitational waves supposedly represent?
We can just barely detect very strong gravitational waves.
@@michaelsommers2356 So why can we not barely detect the high-energy gravitons the waves represent in the gravitational field?
Granted, I realize I'm assuming that anyone thinks there is any possible legitimacy to gravitons, or that gravitational waves are communicated via a gravitational field à la electromagnetic waves and the EM field.
@@LordMarcus The "high energy" gravitons are too weak for us to detect.
@@LordMarcus Understand that the humongous black-hole mergers that we have detected have stretched the four-kilometer-long arms of the detector by about the width of a proton.
@@michaelsommers2356 Ah, see, that I didn't know.
Hmm, so, what would it be like to be really close to one of these events? If the strength of the waves follows the inverse square law, and we're talking a proton's width or less here, and the most recently observed event was just on the fringes of the observable universe, how strong would the waves be if they came from only the other side of the galaxy?
Could the accelerating expansion of the universe be due to the same mechanism as inflation?
How would we measure quintessence, would it be measurable at all?
You make predictions of constant energy density and look for deviations.
Hello guys, where can I ask the questions for the 'listener questions'?
Here on the page. I look at all of them and pick and choose a selection.
@@drdon5205 Ohh okay! Thank you Dr Don 🙏❤️
Can gravitational lensing effect gravitational waves ? Can it focus the gravitational waves just like it does to light ?
This question is pretty deep.
Probably, since the waves travel through space and space is bent by gravitation it seems logical.
Sir , as you said that dark energy is a form of energy , so will it follow the dual principle of reality , it will be both wave and particle and have we found any evidence of any unusual wave or particle , if it has an energy then it should also have a field by following the quantum field theory . Please specify me sir