An excellent lecture - from an excellent speaker - for a general audience (like me). Very clearly explained with a minimum of technical detail. I liked the broad sweep of historical discovery used to put all this dramatic progress in our understanding (yet continuing ignorance) in a proper context. 55:30 This talk was given on 5th March 2014 (according to the show notes). A ground based experiment in the Antarctic, ' BICEP2 ', announced their results just a fortnight later - which gave _the first indirect evidence for inflation_: the _large-scale_ polarisation in the CMB they found can most reasonably be explained only by gravitational waves (not observed directly) whose intensity would not be produced by anything possible in the _current_ universe (from rotating black holes etc) but _would_ be produced under the conditions of inflation. (Therefore inflation)
Naimul Haq I think I understand it like this: it's not that as space expands we are moving away, it's that we are getting stretched and 'scaling' up as the universe grows. I think it's separate from objects in space moving/rotating in space, so a galaxy can be moving towards another and even if it's getting stretched its still moving in the same direction
If a Super Nova is the kickback when the matter in a star is compressed to the point where there is no more room, and a black hole is the result of gravity overcoming that compression. What happens to the neutrons, electrons etc? Are they still present in any meaningful way?
the compression is the result of gravity, in a black hole gravity is overcoming the repulsion between bits of matter. Whether or not they are "present in a meaningful way" depends on what you mean by that... the fate of matter going into a black hole is the subject of debate, search for black hole firewalls, hawking radiation, etc but essentially no one really knows what's going on inside of them. however, it does seem to be the consensus that at the very least the mass is there, i.e. energy going into the black hole is conserved, which I think is a very meaningful way in which the matter is present =)
The simple answer to your question is no: subatomic particles as we know them cease to exist inside of a black hole, although their mass (and hence, their gravity) remain. Scientists don't have any clear idea what actually happens inside a point of infinite density, but they do have some idea how matter gets there. Consider neutron stars: they are also the products of supernovae, but these objects have masses that are less than ~3 solar masses (after the explosion). During the supernova event, most of their electrons are "captured" by the protons due to the overwhelming crush of gravity, forming an extremely dense ball of neutrons (hence the name). So even before we reach a black hole, most electrons cease to exist as such. When the mass of the supernova remnant is greater than 3 solar masses, even the neutrons can't hold each other up and the object continues collapsing until its volume approaches zero.
This the single best lecture on evolution of time space and matter I ever heard. For instance I did not know Hoyle explained the distinct creation mechanism for helium. Everyone else just says the universe had both hydrogen and helium. However, the single best explanation of how we got from one or two species of atoms to 3800 species of minerals is in the lectures "The Origin and Evolution and of Earth" by Robert Hazen available in Great Course lectures from audible.com For instance, not all heavier elements come from supernova. Some are created in Red Giants and dispersed by the solar wind. He explains element creation sequences that include rapid back decays etc. And there were only about a dozen original minerals including, I think diamond.
We are not listening to those microphones directly. There are some speakers, a room, and another microphone in series. The irony being on a lecture about echoes, we are stuck with audio echoes degrading the audio.
Gamma ray bursts and many other types of bursts, may cause the background radiation, how do we know, that this radiation comes from a time when hydrogen or helium did not form, at the big bang? So what was the radiation from? Is there any other possible explanation of the background radiation? When particles and anti-particle annihilated each other, a radiation was emitted, is the background radiation the result of this annihilation or the big bang?Could you kindly explain?
I should point out that I have no qualifications, but I think I can answer your main questions... The interesting thing about the cosmic microwave background (CMB) is that it is almost perfectly uniform in all directions. Gamma ray bursts occur from definite individual sources throughout both space and time, so even if there were several orders of magnitude more of them, the resulting wash of radiation would be much more patchy than the evenly distributed CMB and would not exhibit the perfect blackbody spectrum shown in the video. To really get at the source of the CMB, we need to think about how matter behaves at high energies. If you were to heat a transparent gas such as hydrogen to a temperature of 3000 K, the electrons will dissociate from their atomic nuclei and form a plasma (the 4th state of matter), which has the property of being completely opaque to light. Stars do this. The light you see from a star is only that which escapes the surface: the rest of the body is actually opaque. Scientists believe that when the universe was ~380,000 years old, the temperature of the universe fell below 3000 K for the very first time in history, i.e. the universe's first stable atoms with protons, neutrons, and electrons formed into a gas (mostly hydrogen and helium, which are transparent). Since this occurred everywhere in the universe at more or less the same time, today we still see this evenly distributed light coming from every direction, and as Professor Crawford discusses, the redshift of this light matches exactly with what one would expect given the known expansion of the universe since that early time. As for matter and antimatter annihilation, I believe that this occurred immediately after the Big Bang--probably in less than a second. I hope this answers your questions!
Dear Prof Carolin, I had a problem with the expanding model or the big bang theory, that predicts galaxies moving away from each other at a great speed,either due to expanding space or whatever, that contradicts observation of incessant tumbling of galaxies into each other, in the past and also in the future. I think the issue should be addressed, and possibly explained properly. Could you kindly explain? Thank you.
Hi, I will attempt to answer your question. Scientists call the expansionary force "dark energy" (which simply denotes that they have no idea what it really is or where it comes from). One thing we know about this force is that it is quite weak, but it adds up over extremely large distances. Meanwhile, gravity's effect decreases with distance. Of course, the universe is unimaginably huge, so the effect of dark energy ends up being easily observable (easy for scientists), but only at great distances. The scale required is well beyond the scale of galaxies and even clusters of galaxies, so at the relatively small scale of clusters (huge for us, but small for the universe) gravity dominates, and local galaxies are more or less bound to one another, often colliding/merging as you mentioned. The expansionary force is still there, but it only amounts to roughly 1 km/s per 45,000 lightyears of distance. Andromeda, the nearest galaxy to our own, should therefore be receding at about 55 km/s (because it's 2.5 million lightyears away), but this velocity is actually rather slow astronomically speaking. The Earth orbits the Sun at about 30 km/s, while our own galaxy rotates at over 200 km/s. But if you looked at a galaxy that's, say, a billion lightyears away, you would find it to be receding at over 22,000 km/s, or 7% the speed of light. It may have neighbours to which it is bound by gravity, but relative to us it will appear to be speeding away at 22,000 km/s. I hope I have answered your question!
David Kraemer Leonard Susskind explains how homogeneity and isotropic properties of space renders "no center" of expansion. Does it not also mean what is approaching and what is receding does not have any meaning?
Homogeneity and isotropy are also very large-scale concepts, which are more theoretical in nature than observational. When we look at the nearby universe, things are clearly not homogeneous nor isotropic, because we see a galaxy in one place but not in another, and we see one galaxy moving toward us and another moving away from us. Averaging over very large distances, however, things become generally homogeneous and isotropic. But it is still meaningful to talk about recession, because every galaxy is being carried away from every other galaxy by the expansion or "stretching" of space itself. Because space itself is doing the expanding, the more space you have between two galaxies, the faster they will appear to be separating. So the apparent velocity of recession is proportional to the distance to the object you are observing, given by the equation v=HD where H is Hubble's parameter and D is distance. This holds true no matter where you observe from, whether it's here in the Milky Way or in some galaxy 1 Gly away: any galaxy you look at will appear to be receding faster when it is increasingly further away from you. It isn't erroneous to place oneself at some arbitrary center, because all motion is relative. We don't feel like we're moving, so it is natural to pretend that we are stationary because that's how the universe looks from our point of view.
David Kraemer Recently uploaded video named Laniakea seems more acceptable. Suspicious Observer comments that electrical charges plays a more important role than gravitation, but does not explain. What do you think?
Okay, I have presented you only with observational facts. Laniakea is our home supercluster, and this video does a brilliant job of mapping it for us. But I don't understand why it should be seen to disagree with what I've told you or be "more acceptable." Gravity still acts amid the expansion: its range is technically infinite. Now I couldn't find the commenter you mentioned, but I know that electrical charges or magnetic fields do not act between galaxies, or even stellar systems. Gravity is an additive force, meaning it only increases as you add mass, while electrical charges are both positive and negative and therefore tend to cancel each other over short distances. Gravity is the dominant force acting in superclusters.
When was the actual lecture date? News of polarization results have already come out. So, looking for more current news, this lecture was quite the anti-climax.
Gecko van der waals gravity. if we have a planet and a star, we have less gravitational junction than if we break that planet to form a disk of star surrounding debris. stars in a galaxy form a Gecko van der waals gravitational distribution, also important role play the average inner componental spin times and external times if we slecet average galactic wavefunction of all speeds, spins and stellar rotations, we must mind that the Casimir effect of the void, needs enough space to fade all average inner vs external times of virtual particles of the void. a minor effect also has that the Casimir effect allows because of low quantum noise very few particles not to annihilate
primeval degenerate particle is the correct, there are no singularities, just a wavefunction of inner componetal rotation and external speed, no absolute time/mass there big bang and the black hole cores have degenerate particles, there are no point-like particles the point is perfect, it has absolute time, mass, therefore is man made mistake and religion, not science all particles have a range - inside that they are singularity is a mistake, we know the type does not work if we apply it to singularities, a degenerate particle's range can explain these events - big bang/black hole core degenerate particle if we apply relativistic external/internal time with a beholding range of time and space virtual beholders - beholding wavefuntion we need multilayer beholding wavefunction and not absolute religious singularity pointlike mistakes
Carolin Crawford ... astronomical Superhero!
Good answere Mr Sebastian
We as humans are in a way the universe exploring and viewing itself.
An excellent lecture - from an excellent speaker - for a general audience (like me). Very clearly explained with a minimum of technical detail. I liked the broad sweep of historical discovery used to put all this dramatic progress in our understanding (yet continuing ignorance) in a proper context.
55:30 This talk was given on 5th March 2014 (according to the show notes). A ground based experiment in the Antarctic, ' BICEP2 ', announced their results just a fortnight later - which gave _the first indirect evidence for inflation_: the _large-scale_ polarisation in the CMB they found can most reasonably be explained only by gravitational waves (not observed directly) whose intensity would not be produced by anything possible in the _current_ universe (from rotating black holes etc) but _would_ be produced under the conditions of inflation. (Therefore inflation)
I think I've watched almost all of Carolin's lecture's, thank you!
so have i! haha isn't she great?
Her train of thought is unbreakable.
Naimul Haq I think I understand it like this: it's not that as space expands we are moving away, it's that we are getting stretched and 'scaling' up as the universe grows. I think it's separate from objects in space moving/rotating in space, so a galaxy can be moving towards another and even if it's getting stretched its still moving in the same direction
Thank you Professor Crawford.
What a great lecturer!
Would be nice to see this lecture with the polarization results included.
If a Super Nova is the kickback when the matter in a star is compressed to the point where there is no more room, and a black hole is the result of gravity overcoming that compression. What happens to the neutrons, electrons etc? Are they still present in any meaningful way?
the compression is the result of gravity, in a black hole gravity is overcoming the repulsion between bits of matter.
Whether or not they are "present in a meaningful way" depends on what you mean by that... the fate of matter going into a black hole is the subject of debate, search for black hole firewalls, hawking radiation, etc but essentially no one really knows what's going on inside of them. however, it does seem to be the consensus that at the very least the mass is there, i.e. energy going into the black hole is conserved, which I think is a very meaningful way in which the matter is present =)
The simple answer to your question is no: subatomic particles as we know them cease to exist inside of a black hole, although their mass (and hence, their gravity) remain. Scientists don't have any clear idea what actually happens inside a point of infinite density, but they do have some idea how matter gets there.
Consider neutron stars: they are also the products of supernovae, but these objects have masses that are less than ~3 solar masses (after the explosion). During the supernova event, most of their electrons are "captured" by the protons due to the overwhelming crush of gravity, forming an extremely dense ball of neutrons (hence the name). So even before we reach a black hole, most electrons cease to exist as such. When the mass of the supernova remnant is greater than 3 solar masses, even the neutrons can't hold each other up and the object continues collapsing until its volume approaches zero.
Thank you both for your answers, they are very enlightening.
This the single best lecture on evolution of time space and matter I ever heard. For instance I did not know Hoyle explained the distinct creation mechanism for helium. Everyone else just says the universe had both hydrogen and helium.
However, the single best explanation of how we got from one or two species of atoms to 3800 species of minerals is in the lectures "The Origin and Evolution and of Earth" by Robert Hazen available in Great Course lectures from audible.com
For instance, not all heavier elements come from supernova. Some are created in Red Giants and dispersed by the solar wind. He explains element creation sequences that include rapid back decays etc. And there were only about a dozen original minerals including, I think diamond.
Was the background radiation at one time where the earth is now?
We are not listening to those microphones directly. There are some speakers, a room, and another microphone in series. The irony being on a lecture about echoes, we are stuck with audio echoes degrading the audio.
Gamma ray bursts and many other types of bursts, may cause the background radiation, how do we know, that this radiation comes from a time when hydrogen or helium did not form, at the big bang? So what was the radiation from? Is there any other possible explanation of the background radiation? When particles and anti-particle annihilated each other, a radiation was emitted, is the background radiation the result of this annihilation or the big bang?Could you kindly explain?
I should point out that I have no qualifications, but I think I can answer your main questions...
The interesting thing about the cosmic microwave background (CMB) is that it is almost perfectly uniform in all directions. Gamma ray bursts occur from definite individual sources throughout both space and time, so even if there were several orders of magnitude more of them, the resulting wash of radiation would be much more patchy than the evenly distributed CMB and would not exhibit the perfect blackbody spectrum shown in the video.
To really get at the source of the CMB, we need to think about how matter behaves at high energies. If you were to heat a transparent gas such as hydrogen to a temperature of 3000 K, the electrons will dissociate from their atomic nuclei and form a plasma (the 4th state of matter), which has the property of being completely opaque to light. Stars do this. The light you see from a star is only that which escapes the surface: the rest of the body is actually opaque. Scientists believe that when the universe was ~380,000 years old, the temperature of the universe fell below 3000 K for the very first time in history, i.e. the universe's first stable atoms with protons, neutrons, and electrons formed into a gas (mostly hydrogen and helium, which are transparent). Since this occurred everywhere in the universe at more or less the same time, today we still see this evenly distributed light coming from every direction, and as Professor Crawford discusses, the redshift of this light matches exactly with what one would expect given the known expansion of the universe since that early time.
As for matter and antimatter annihilation, I believe that this occurred immediately after the Big Bang--probably in less than a second. I hope this answers your questions!
Dear Prof Carolin, I had a problem with the expanding model or the big bang theory, that predicts galaxies moving away from each other at a great speed,either due to expanding space or whatever, that contradicts observation of incessant tumbling of galaxies into each other, in the past and also in the future. I think the issue should be addressed, and possibly explained properly. Could you kindly explain? Thank you.
Hi, I will attempt to answer your question.
Scientists call the expansionary force "dark energy" (which simply denotes that they have no idea what it really is or where it comes from). One thing we know about this force is that it is quite weak, but it adds up over extremely large distances. Meanwhile, gravity's effect decreases with distance. Of course, the universe is unimaginably huge, so the effect of dark energy ends up being easily observable (easy for scientists), but only at great distances. The scale required is well beyond the scale of galaxies and even clusters of galaxies, so at the relatively small scale of clusters (huge for us, but small for the universe) gravity dominates, and local galaxies are more or less bound to one another, often colliding/merging as you mentioned. The expansionary force is still there, but it only amounts to roughly 1 km/s per 45,000 lightyears of distance. Andromeda, the nearest galaxy to our own, should therefore be receding at about 55 km/s (because it's 2.5 million lightyears away), but this velocity is actually rather slow astronomically speaking. The Earth orbits the Sun at about 30 km/s, while our own galaxy rotates at over 200 km/s. But if you looked at a galaxy that's, say, a billion lightyears away, you would find it to be receding at over 22,000 km/s, or 7% the speed of light. It may have neighbours to which it is bound by gravity, but relative to us it will appear to be speeding away at 22,000 km/s. I hope I have answered your question!
David Kraemer
Leonard Susskind explains how homogeneity and isotropic properties of space renders "no center" of expansion. Does it not also mean what is approaching and what is receding does not have any meaning?
Homogeneity and isotropy are also very large-scale concepts, which are more theoretical in nature than observational. When we look at the nearby universe, things are clearly not homogeneous nor isotropic, because we see a galaxy in one place but not in another, and we see one galaxy moving toward us and another moving away from us. Averaging over very large distances, however, things become generally homogeneous and isotropic.
But it is still meaningful to talk about recession, because every galaxy is being carried away from every other galaxy by the expansion or "stretching" of space itself. Because space itself is doing the expanding, the more space you have between two galaxies, the faster they will appear to be separating. So the apparent velocity of recession is proportional to the distance to the object you are observing, given by the equation v=HD where H is Hubble's parameter and D is distance. This holds true no matter where you observe from, whether it's here in the Milky Way or in some galaxy 1 Gly away: any galaxy you look at will appear to be receding faster when it is increasingly further away from you. It isn't erroneous to place oneself at some arbitrary center, because all motion is relative. We don't feel like we're moving, so it is natural to pretend that we are stationary because that's how the universe looks from our point of view.
David Kraemer
Recently uploaded video named Laniakea seems more acceptable. Suspicious Observer comments that electrical charges plays a more important role than gravitation, but does not explain. What do you think?
Okay, I have presented you only with observational facts. Laniakea is our home supercluster, and this video does a brilliant job of mapping it for us. But I don't understand why it should be seen to disagree with what I've told you or be "more acceptable." Gravity still acts amid the expansion: its range is technically infinite.
Now I couldn't find the commenter you mentioned, but I know that electrical charges or magnetic fields do not act between galaxies, or even stellar systems. Gravity is an additive force, meaning it only increases as you add mass, while electrical charges are both positive and negative and therefore tend to cancel each other over short distances. Gravity is the dominant force acting in superclusters.
But, what if you turn off all the light (stars) off? does the cosmic microwave back ground,
the CMB, become hotter?
03:12 "... that photon can be traveling across the universe minding its own business..."
lololol I LOVE listening to her talk.
If a photon undergoes a redshift it loses energy equivalent to h*c(1/lambda1 - 1/lambda2) ... where does the energy go?
brilliant, that's baby picture of universe.
When was the actual lecture date? News of polarization results have already come out. So, looking for more current news, this lecture was quite the anti-climax.
Wednesday, 5 March 2014 - 1:00pm. That would be before the announcement of the polarization results.
Gecko van der waals gravity.
if we have a planet and a star, we have less gravitational junction
than if we break that planet to form a disk of star surrounding debris.
stars in a galaxy form a Gecko van der waals gravitational distribution,
also important role play the average inner componental spin times
and external times if we slecet average galactic wavefunction of all speeds, spins and stellar rotations,
we must mind that the Casimir effect of the void, needs enough space to fade all average inner vs external times of virtual particles of the void.
a minor effect also has that the Casimir effect allows because of low quantum noise very few particles not to annihilate
primeval degenerate particle is the correct,
there are no singularities, just a wavefunction of inner componetal rotation and
external speed, no absolute time/mass
there big bang and the black hole cores have degenerate particles,
there are no point-like particles
the point is perfect, it has absolute time, mass, therefore is man made mistake
and religion, not science
all particles have a range - inside that they are
singularity is a mistake, we know the type does not work if we apply it
to singularities, a degenerate particle's range can explain
these events - big bang/black hole core degenerate particle
if we apply relativistic external/internal time with a beholding range of time and space virtual beholders - beholding wavefuntion
we need multilayer beholding wavefunction and not absolute religious singularity pointlike mistakes