Skip to playerSkip to main content
TV Hub
  • 2 days ago

Category

📺
TV
Transcript
00:00The End
00:30fighting rough is not expected of scientists yet modern cosmology the
00:35science of the universe is ringing to the sound of punch and counterpunch at
00:41root the fight is over how fast the universe is getting bigger at stake a
00:46substantial reputations and the status of the most widely accepted theory in
00:51cosmology the Big Bang the argument was started by the American astronomer
00:57Edwin Powell Hubble himself a useful boxer in 1929 he discovered that all of
01:04the galaxies in space were rushing away from earth it seemed to Hubble that the
01:10universe was expanding the old idea that it was a fixed and static place was
01:16demolished with a single blow when I first took up astronomy I was drawn to a
01:23study of the light spectrum of different galaxies to us light may appear white or
01:30yellow but it is in fact composed of bands of different color with each color
01:34corresponding to a different wavelength this is called the spectrum most
01:39commonly seen in the rainbow I was surprised to find that the spectra I
01:44measured were all tending to the red side this phenomena can be compared to the
01:49Doppler effect which occurs when the pitch of a moving sound source alters as it
01:54approaches us and then recedes away much like a passing car or a speeding train as it whizzes by
02:06as the galaxies themselves recede the spectra turns a little red as they
02:11approach us they appear bluer I realize that if all the spectra are shifted red then all the
02:19galaxies must be receding this strongly suggested to me that the universe itself
02:25was expanding I found furthermore that the greater the distance away of the
02:30galaxies the greater the receding velocity this proportionality indicated a general
02:36rate of expansion which is I believe called the Hubble constant thank you
02:49galaxies galaxies receding receding receding the universe the universe the universe expanding
03:04the universe expands it gets bigger and bigger and the further you go out from us
03:10the faster galaxies the faster galaxies recede from us and the Hubble constant very simply measures the increase of speed per step you go out
03:22this means that a galaxy twice as far away from us is moving twice as fast the Hubble constant then can be a vital practical tool to establish distances in the universe
03:28and that's not all well to a cosmologist the Hubble constant is perhaps the most important number in part because it sets the scale of the universe I mean that is the fundamental reason it sets the sizes of everything that we look at it sets the luminosities of all the galaxies that we look at it sets the age of the universe
03:46and we need to need to understand that if we really want to talk about the model as a whole and understand where we've come from how galaxies have formed how stars have formed the problem is astronomers have so far been unable to pin down
03:56It sets the age of the universe.
03:58And we need to understand that if we really want to talk about the model as a whole
04:03and understand where we've come from, how galaxies have formed, how stars have formed.
04:08The problem is, astronomers have so far been unable to pin down the value of the Hubble constant.
04:15Is the universe expanding quickly or slowly?
04:18Is the Hubble constant high or is it low?
04:22I bet for high H.
04:24A Hubble constant of 80.
04:25If I had a gun pointed at my head and I had no choice,
04:28I would say that the Hubble constant is very likely less than 50.
04:32The value of H0 that we derive from the planetary nebula method is about 80.
04:37It may be as low as 40.
04:39I get a value for the Hubble constant of 70.
04:44My personal best bet at the moment is 50.
04:48The Hubble constant is 85.
04:5050 or lower.
04:52I'd vote for 80.
04:52How can there be so many different values?
04:58One major reason is that the huge size of the universe makes it very difficult to measure.
05:04But underlying the technical problems is something bigger and more important.
05:09If the Hubble constant is high, it means that the universe is young.
05:14Younger, perhaps, than the oldest stars in it.
05:17This is simply not possible.
05:20If the Hubble constant turned out to be high, it would be very interesting,
05:25and it could pose problems for the standard model for the expanding universe.
05:30The reason is simple to see.
05:32The Hubble constant is simply the measure of the rate of expansion of the universe.
05:36The larger the Hubble constant, the greater the rate of expansion,
05:40and therefore, the less time it took for the universe to have expanded
05:44from an intolerably dense state to where we are now.
05:46Now, of course, nothing in the universe, no stars, no heavy elements,
05:51can be older than the time it took for the universe to expand
05:54from that intolerably dense state to where it is now.
05:57So if we have a believable theory, we better have a consistent theory
06:01in which stars and the heavy elements are younger than the universe.
06:05The standard model of the evolution of the universe is called the Big Bang.
06:12It's clear that Hubble was right.
06:14The universe is expanding.
06:17Less clear, though, is what that means.
06:19We don't, for instance, feel ourselves expanding,
06:22and the Earth doesn't seem to be getting any bigger.
06:24So what is really expanding?
06:28I think one of the best ways to understand what an expanding universe is
06:32is by a little toy here.
06:36Look at these three little things and focus your attention
06:38on the little hockey player here.
06:41As the universe expands, the speed of motion away from this thing
06:46is proportional to how far away you are.
06:49But look at this.
06:49Supposing we focus now on the guy in the middle,
06:52and we do the same thing.
06:54He sees the universe is expanding about him.
06:57Now let's focus attention on the one on the right.
07:00Again, he sees the universe expanding around him.
07:03So this funny distance is proportional to velocity
07:07or velocity is proportional to distance
07:09has the consequence that the universe looks the same to everybody.
07:12As far as everyone's concerned, he's the center of the universe.
07:15I think a very good picture of the expanding universe
07:19is a cake you bake in your oven.
07:24The cake contains yeast, and the yeast drives your cake to expand.
07:29And if you even imagine in the cake some raisins,
07:35and the raisins corresponding to the galaxies move all away from each other.
07:42You can have a yardstick, which at some time is very small and at some time is very big.
07:48And in fact, the best way to describe the expansion of the universe
07:50is not in terms of, and this may be a little technical,
07:55but is not in terms of this idea that galaxies are moving away from us,
07:59because that's not really right.
08:02It's that they appear to be moving away from us.
08:04In fact, what's happening is that the fabric of space,
08:07the dimensionality, the yardstick is changing, is stretching.
08:11The Big Bang was the brainchild of a Belgian priest
08:20called Georges-Henri Lemaitre, working in the late 1920s.
08:25Lemaitre argued that all of space was created from a single packet of energy.
08:30Like a living cell, the packet divided and multiplied,
08:33eventually forming all of the universe.
08:36Many of the leading scientists of the time, Einstein included, were hostile.
08:40The theory is dependent, to a large extent, upon the peculiar and contradictory nature of time,
08:57which is not quite as straightforward as you might think.
09:02The equations of physics do not really distinguish
09:05between the backward and the forward direction of time.
09:08Yet, we're all painfully aware that time does have a preferred direction.
09:15We grow older, not younger.
09:18We can remember the past, we don't remember the future.
09:21And the universe evolves from a state, from an organized state, into a disorganized state.
09:27And time's arrow tells us that the universe had a past, that it had a beginning.
09:40The Big Bang Theory says that the universe began in a cataclysmic explosion several billion years ago.
09:48At that time, all the material in the universe was concentrated into an area of extreme density,
09:54totally smooth and incredibly hot.
09:56At the beginning, this super-dense matter expanded with unimaginable violence.
10:03Everything flew apart.
10:05As the universe expanded, it cooled and evolved into the huge, cold, empty place we see today.
10:13The notion that everything came from one speck of space is extraordinary.
10:29And the Big Bang Theory does have its detractors.
10:32Even the name itself, coined by Sir Fred Hoyle,
10:35was intended to ridicule the idea of an explosion creating anything.
10:40Nevertheless, it's backed up with hard evidence.
10:43The Big Bang Theory has to be recognized as being more than just some kind of a cartoon image
10:47of a big explosion from which the universe came.
10:50It really is a detailed mathematical theory.
10:52And given this mathematical description of the details,
10:56you can actually calculate the rates of different nuclear reactions
10:59that would have taken place in the early universe,
11:02the way in which protons and neutrons would collide and sometimes stick together and sometimes fly apart.
11:07The theory predicts with extreme accuracy the proportions of the elements
11:14that were made in the soup of particles created in the Big Bang.
11:17It's rather like having a theory that can take vegetable soup,
11:22work back through the process of making it, and predict what the ingredients were.
11:27When the theoretical predictions of the Big Bang are tested in experiments on Earth,
11:36they produce exactly the right amounts of the light elements hydrogen, helium, and lithium,
11:42the cabbages, carrots, and tomatoes of Big Bang soup.
11:46These elements themselves combine to produce all the different things we now see in the universe,
11:53including us.
11:55And that's not all the Big Bang's got going for it.
11:59More support comes from the surviving radiation of the hot Big Bang,
12:03the dimly glowing embers of what was once the fire of creation.
12:06The more we've measured the properties of this radiation,
12:10the more we've discovered that it conforms to exactly what the Big Bang theory predicts.
12:15Number one, the radiation is extremely uniform in all directions,
12:19no matter where you look, it's the same.
12:22Secondly, the Big Bang theory makes a prediction for the spectrum of the light,
12:26the way in which the intensity changes as you look at different wavelengths.
12:31Over the years, people have been trying to measure it more precisely,
12:34and by now the far, by far the most precise measurements we have
12:37come from the COBE satellite,
12:39and it's in absolutely gorgeous agreement
12:42with the predictions of the thermal radiation from the heat of the Big Bang.
12:48The strength of the evidence for the Big Bang
12:51makes it the cornerstone of modern cosmology.
12:54But the theory requires the universe to be a certain age.
12:58Time, and a lot of it,
13:00is needed for stars to condense and galaxies to form.
13:03If the Hubble constant is high,
13:05then the expansion is fast and the universe is young,
13:09almost certainly too young for these processes to have taken place.
13:13This poses a serious problem for the Big Bang
13:16and is a major reason why we want to measure the Hubble exactly.
13:20So, how do we go about it?
13:23The Hubble constant is in fact
13:25the ratio of the speed to the distance.
13:30So, it's a speed divided by the distance.
13:33And so, it's measured in units of kilometers per second per speed
13:37divided by megaparsec.
13:40A megaparsec is a unit of distance that astronomers use.
13:43It's approximately three and a third million light years,
13:47or the distance light would travel
13:49in about three and a third million years.
13:51The nearest major galaxy to our own,
13:54the Andromeda galaxy,
13:56something we see pictures of pretty often,
13:58that is almost a megaparsec away.
14:03It's worth remembering that the speed of light
14:06and the distances you can measure with it
14:08are crucial to cosmology.
14:09The speed of light is enormous.
14:13That's why it appears to be an instantaneous phenomenon.
14:16In fact, it isn't.
14:18Light travels at about 300,000 kilometers every second.
14:22And at this extraordinary speed,
14:24light could travel around the Earth
14:26seven times in just one second.
14:29This means that a megaparsec
14:31is an exceedingly large distance.
14:33To measure the constant,
14:37we need to know only two things,
14:39the velocity of a galaxy
14:40and the distance it is away from us.
14:44Calculating the speed is relatively easy.
14:46You only have to measure the red shift.
14:48The greater the shift,
14:50the faster the galaxy is moving away.
14:54This red shift gives you
14:55directly the recession velocity of the galaxy,
14:59no problem.
14:59The big problem is
15:02to measure also the distance to that galaxy.
15:06And there,
15:08if you wanted an equation
15:10to determine the Hubble constant,
15:12the Hubble constant is simply
15:13the recession velocity,
15:15V,
15:16divided by the distance,
15:18D,
15:19of a given galaxy.
15:22Well, the irony
15:24in determining a Hubble constant
15:26is that
15:28you're trying to measure
15:29the distances to galaxies
15:31with the Hubble constant.
15:33But in order to determine
15:34the Hubble constant,
15:36you have to have
15:37a distance,
15:38a very accurate distance,
15:39to a galaxy.
15:41The idea is,
15:42if we can measure
15:43one distance,
15:44one distance,
15:45and determine the Hubble constant
15:47very accurately,
15:48then we can go out
15:49and measure the distances
15:50to all of the galaxies around.
15:52This irony could be resolved
15:55if we could measure exactly
15:57the distance to just
15:58one receding galaxy,
16:00but not any old one,
16:02because some of them
16:03are not receding at all.
16:04They're actually coming towards us.
16:08The gravitational forces
16:10of galaxies on each other
16:12cause motions to occur.
16:14And the velocity you see
16:15that any given galaxy has
16:17isn't really the velocity
16:19it should have
16:20based on just the expansion
16:21of the universe.
16:23And the best example
16:24that I can give you
16:24is a very simple one.
16:26The nearest big galaxy
16:27to our own
16:28is the Andromeda galaxy.
16:29And rather than expanding
16:30away from us,
16:32because of our mutual
16:33gravitational attraction,
16:36Andromeda and the Milky Way
16:37are falling towards each other.
16:39The mutual gravity
16:40amongst neighboring galaxies
16:42disturb this general expansion.
16:44So the quest, then,
16:46is to go to as large
16:47a distance as possible
16:48where we can assume
16:49that we have a fair
16:50representation of the universe
16:53as a whole,
16:54and therefore the expansion
16:55is smooth in the so-called
16:57Hubble flow.
16:59But on the other hand,
17:00we don't want to go so far
17:01that the methods
17:02that we use
17:03to estimate distances
17:04break down.
17:06That's a tricky problem
17:08because your ability
17:09to measure the distances
17:10of galaxies
17:11is a function
17:13of how far away they are.
17:15It's easy to measure
17:15the distances
17:16to the ones
17:17in your backyard.
17:17It's much harder
17:19to measure the distances
17:20to things
17:20that are very far away.
17:24And when astronomers
17:26say far away,
17:27they don't mean
17:28as far as the sun
17:29or even the nearest galaxies.
17:31They're talking about distances
17:32that are literally
17:33astronomical.
17:34If we consider
17:39our nearest neighbor
17:40the moon,
17:40that's some 250,000 miles
17:43away from us.
17:44And light is going
17:45to take an appreciable time
17:46to reach the moon,
17:47about a second and a quarter,
17:49such that if astronauts
17:50are on the moon
17:51and you're communicating
17:52with them,
17:53there's a small time delay
17:54in your saying something
17:56in their response.
17:57Going to the sun,
17:59it is some 93 million miles
18:01from the earth,
18:02and light takes about
18:03eight minutes to get
18:04from the sun
18:05to the earth.
18:06The nearest star
18:07to the sun
18:08is called Proxima Centauri,
18:09and that is a discouragingly
18:11long distance from us.
18:12It would take light
18:13some four and third years
18:14to get from Proxima Centauri
18:16to the sun.
18:17It's also important
18:18to realize the space
18:19between us
18:20and Proxima Centauri
18:21is virtually nothing.
18:23Now, the whole Milky Way,
18:24which we're all part of,
18:26is some 60,000 light years
18:28in diameter.
18:31Now, the Andromeda galaxy
18:32is a galaxy
18:34much like the Milky Way.
18:36It's our nearest
18:37large galaxy neighbor,
18:39and that's some 2 million
18:40light years distance from us.
18:43The Virgo cluster of galaxies
18:45is some 50, 60 million
18:47light years distance from us.
18:50And another prominent cluster,
18:51the Coma cluster,
18:52is some 250 million
18:54light years from us.
18:55Virgo and Coma
19:00are far enough away
19:01to make them useful
19:02for measuring the Hubble.
19:03But even their vast distances
19:05are nothing compared
19:06to the gulf between us
19:08and the farthest known
19:09cosmic objects,
19:10quasars,
19:12which are used in some
19:12of the most up-to-date
19:13distance measurements.
19:16Quasars are thought to be
19:177 to 10 billion
19:18light years away.
19:20The sun is a mere
19:21eight light minutes.
19:23How can we even begin
19:24to envisage such
19:25enormous distances?
19:29Well,
19:30if the observable universe
19:31is the same size
19:32as the journey
19:33from Brighton to London,
19:35that is 50 miles,
19:36then the furthest quasars
19:38are about 25 miles away
19:40at Gatwick Airport.
19:42The Coma cluster
19:49will be found in Battersea,
19:51while the Virgo cluster
19:52will be found
19:53as you approach
19:54the outside
19:55of Victoria Station.
19:57The nearest galaxy,
19:59Andromeda,
20:00is a mere 20 yards
20:02from the end
20:02of the platform.
20:05Our own galaxy,
20:06the Milky Way,
20:07is only one foot across,
20:09and the radius
20:10of the solar system
20:11is a hundredth
20:12of the width
20:12of a piece of paper.
20:15It would take
20:16the Voyager spacecraft
20:173,000 years
20:19to travel across
20:20this minuscule edge.
20:21The unimaginable scale
20:40of the universe
20:41has so far resisted
20:42the astronomers' efforts
20:43to measure distances accurately,
20:45and to calculate
20:46the Hubble constant
20:47with any degree of certainty.
20:49But a range
20:50of new measuring techniques
20:51are now being brought
20:52to bear on the problem,
20:54working in concert
20:54with some of the oldest
20:56known to man.
20:59The ideal way
21:01of measuring distances
21:02would be
21:03the surveyor's method
21:04of triangulation,
21:06where you have a baseline
21:07whose distance you know,
21:08measure the direction
21:09to some distant point
21:12from the two ends
21:13of the baseline,
21:14and hence you estimate
21:15the distance.
21:15That's how surveyors
21:16measure distances on the Earth.
21:18Now we can do that
21:18in astronomy
21:19using the orbit
21:22of the Earth
21:23around the Sun
21:23as the baseline.
21:25But unfortunately
21:26this only works
21:27for relatively nearby stars.
21:30And so if we want
21:30to reach out
21:31to even greater distances
21:32to move up
21:33the cosmological distance ladder,
21:35we have to find
21:36other methods.
21:38And measuring
21:39very large distances
21:40is essential
21:41to settling
21:42the value of the Hubble.
21:44One way to reach further
21:45is to find
21:46what's called
21:47a standard candle,
21:48a light source
21:49out there in the universe
21:50whose power
21:51you can know for sure,
21:52like the wattage
21:53of a light bulb.
21:55If we have a source
21:57of radiation
21:57whose total luminosity,
21:59whose intrinsic output,
22:01intrinsic power,
22:02we know,
22:03we know how many watts
22:04it's putting out,
22:05then as that source
22:08gets further and further
22:09away from us,
22:10it looks dimmer and dimmer,
22:11the brightness goes down,
22:13and it goes down
22:14by what's called
22:15the inverse square law
22:16of radiation,
22:17that as you double
22:19the distance,
22:20the brightness
22:20goes down by four.
22:23If you triple the distance,
22:24it goes down by nine
22:25and so on.
22:26So if we know
22:27the power output
22:28of any kind of source
22:29and we measure
22:31the brightness of it,
22:32then we can work out
22:33how far away it is.
22:35Sounds simple enough,
22:37but determining
22:37how bright something
22:38really is
22:39is fraught with difficulty.
22:42Imagine, for instance,
22:43three light bulbs,
22:44each of a different size
22:45and wattage.
22:46They could appear
22:47to be very similar
22:48in brightness,
22:50but be at completely
22:51different distances
22:51from us.
22:53It's the same
22:54with stars and galaxies.
22:57Fortunately,
22:58there do exist
22:58cosmic yardsticks,
23:00the pulsating stars
23:01called Cepheid variables.
23:04Decades of observations
23:05have confirmed
23:06that all Cepheids
23:07have the same
23:08valuable quality.
23:10Cepheids are stars
23:11that are variable stars.
23:12They pulsate
23:14and how long
23:16they pulsate for,
23:17their pulsation period,
23:19is related
23:19to their brightness.
23:21Really bright Cepheid variables,
23:23the 150-watt light bulbs,
23:26pulsate with really long periods
23:27where really long
23:28is 100 days.
23:30And really dim Cepheid variables,
23:32the 20-watt light bulbs
23:34or 15-watt light bulbs,
23:35pulsate with periods
23:36that are around five days.
23:37And that means
23:38they're sort of like
23:39searchlight beacons.
23:40You can find one
23:41very easily,
23:42and if you find one
23:43and measure its period
23:44and measure its brightness,
23:46you know pretty much
23:46how far away it is.
23:48Again,
23:49sounds simple enough.
23:51The snag this time is
23:52that Cepheids
23:53are dim stars,
23:54only visible
23:55in nearby galaxies.
23:57So astronomers try
23:58to find a brighter
23:59standard candle
24:00which they can see
24:00much further out,
24:02something like a supernova,
24:04a gigantic exploding star.
24:06All supernovae
24:15are thought to produce
24:16about the same amount
24:17of light,
24:18something that appealed
24:19to Alan Sandage
24:20and Gustav Tumann.
24:22It makes a fantastic
24:23light flash,
24:25as bright as
24:26one billion suns
24:28for a few days,
24:30and you see these objects
24:32far, far out,
24:34and it's each time
24:35this mass becoming
24:37unstable and exploding,
24:39so one expects
24:40them to be always
24:41equally bright,
24:43and if you can
24:45calibrate
24:46this luminosity
24:48in some galaxy
24:50whose distance
24:51you know already
24:52through Cepheids,
24:54you know
24:54your standard candle.
24:57And by again
24:58using the inverse
24:59square law,
25:00you can know
25:00the distance.
25:02There are other
25:02standard candles.
25:03some astronomers
25:05use luminous gas
25:06clouds called
25:06planetary nebulae.
25:09Some average out
25:10the brightest patches
25:11in whole galaxies
25:12and use that
25:13as their standard.
25:15Still others
25:16have started to
25:17exploit different
25:17characteristics of
25:18galaxies to measure
25:19distance,
25:20specifically the way
25:22they move.
25:24For a particular
25:24type of galaxy,
25:26a spiral galaxy,
25:27they are intrinsically
25:29quite flat,
25:30sort of like a pancake
25:31or a disc,
25:32and this disc
25:33is rotating.
25:35And the bigger
25:35the galaxy,
25:37the faster it has
25:38to rotate in order
25:39to counteract
25:39the effects of gravity.
25:41And the brighter
25:42the galaxy,
25:43the more massive
25:44it tends to be
25:45and the faster
25:46it has to rotate
25:46in order to be
25:47in a stable situation.
25:49So, the bottom line
25:51then is that
25:51a brighter galaxy
25:52will rotate faster
25:54than a fainter galaxy,
25:56and when we then
25:56want to go out
25:57and estimate the distance
25:58to any particular galaxy,
26:01we measure its speed
26:02of rotation,
26:03and using this relationship
26:05we have a prediction,
26:07an idea,
26:08of how intrinsically
26:09bright the galaxy is.
26:11We then measure
26:12its apparent brightness,
26:14and that difference
26:15through the inverse
26:15square law
26:16allows us to estimate
26:17the distance.
26:19There are other,
26:21more direct ways
26:22to measure distance,
26:23among them the technique
26:24known as
26:25gravitational lensing.
26:27When light from
26:28a distant galaxy
26:29passes through
26:29another intervening galaxy,
26:31it's bent.
26:33The degree of bending
26:34can be used
26:35to calculate
26:35the distance
26:36to the far galaxy.
26:38These techniques
26:39are so far
26:39comparatively limited
26:40and highly speculative,
26:42but they do point
26:43to a low Hubble.
26:48So many methods,
26:49each with its own claim
26:50to accuracy
26:51and consistency.
26:53Has all this
26:54galactic surveying
26:55brought us any closer
26:56to settling the Hubble
26:57trouble?
27:01The value of H-naught
27:02that we derive
27:03from the planetary
27:03nebula method
27:04is about 80.
27:06My belief
27:07on the Hubble constant
27:08stems from a 30-year-long
27:11collaboration
27:12with Alan Sandwich,
27:13and we get
27:1550 kilometers
27:16per second
27:17per megaparsec.
27:19if one dismisses
27:21the idea
27:22that somehow
27:22the local galaxies
27:23are fundamentally
27:24different
27:25than the more
27:26distant ones,
27:27and I see
27:27no reason
27:29to assume
27:29such a thing,
27:30then I have to
27:31accept that
27:32the Hubble constant
27:33is 85.
27:38The difference
27:39between 50 and 85
27:41might not seem much,
27:43but it means
27:44that the universe
27:44could be 14 billion
27:46rather than 8 billion
27:47years old,
27:49a crucial difference.
27:51Scientific arguments
27:52about the best way
27:53to measure distance
27:53are one reason
27:54for the discrepancy,
27:55but not the only one.
27:58In science,
27:59people get attached
28:00to their results,
28:01perhaps too attached.
28:04One such example
28:05is the rivalry
28:06between two giants
28:07of the field,
28:09the French-born
28:09astronomer
28:10Gerard de Vaucaleur
28:11and the man
28:12who was seen
28:13as Hubble's heir,
28:14Alan Sandwich.
28:15Sandwich kept working
28:18on the problem,
28:19the Vaucaleurs
28:19kept working
28:20on the problem,
28:21and one other person
28:22got into the game
28:23in the 1960s
28:24was Sidney Vandenberg,
28:25a Canadian astronomer,
28:27and the three of them
28:28went their own ways.
28:30The Vaucaleurs
28:31continued to want
28:32to measure
28:32a value
28:33that was near 100,
28:34and Vandenberg
28:35sort of went
28:35in that same direction,
28:37whereas Sandwich's values
28:38kept getting smaller
28:39and smaller
28:39as he refined
28:40his measurements
28:41and the like.
28:41One of the problems
28:44is that
28:45people tend
28:48to overestimate
28:49the accuracy
28:50of the measurements
28:51they make,
28:52so they assert
28:54that the Hubble constant
28:55has this value
28:55or that value,
28:57when really
28:57all they can say
28:58is that it has
28:59a range of values,
29:01and people
29:02who work in this field
29:03seem to have a,
29:05seem to become
29:07possessed
29:07by a terrible certainty
29:09that they know
29:09the value
29:10of the Hubble constant.
29:10This is one of the
29:11afflictions
29:12of this field.
29:14The sad part
29:15about the story
29:15at that time
29:16was that
29:16it was actually
29:18very difficult
29:18for any of the
29:19younger people
29:19who might be interested
29:20to begin working
29:21in the field
29:22because these giants
29:23dominated it,
29:24and they would
29:24pretty much squash
29:26any attempt
29:27to come up
29:28with answers
29:29other than their own.
29:30They're sort of,
29:31you know,
29:31the great warring camps.
29:33You know,
29:33I say it's 50,
29:35you say it's 100,
29:36okay,
29:37and they have
29:37methods over here
29:39and methods over there,
29:40they're all screwball,
29:41they don't look
29:41at the same things.
29:43There's a few people
29:43doing it
29:44and you can never
29:44put it together.
29:46All the new methods,
29:48all the people
29:48who come in
29:49with no previous history
29:50are more or less
29:51consistently getting
29:52these larger values,
29:53the Hubble kinds.
29:54And so that's
29:55one indication
29:55that, at least
29:56with some people,
29:57there's convergence.
30:00We seem to have
30:01four new methods
30:02for measuring the Hubble
30:03which all get
30:04a high value.
30:06The one employed
30:07by Sandage and Taman
30:08still gets a low value.
30:10Maybe we should look
30:11again at their evidence.
30:13Vital to Sandage's claims
30:15is a supernova
30:16which exploded
30:17back in 1937.
30:19This was photographed
30:20first by astronomers
30:21Walter Bader
30:22and Fritz Zwicky.
30:24Michael Pierce
30:25has been examining
30:26the original photographs.
30:28George Jacoby and I
30:30have been analyzing
30:31the plates
30:32with modern techniques
30:33and have found
30:34that the supernova
30:35was in fact
30:37considerably fainter
30:38than Bader
30:39and Zwicky
30:39had claimed
30:40in their papers
30:42at that time
30:43and that this
30:45correction alone
30:47would revise,
30:48say,
30:48the Sandage
30:49and Taman picture
30:50from a Hubble constant
30:51of about 50
30:52up to around 60
30:53to 65.
30:55The other contentious issue
30:57is whether supernovae
30:58are good standard
30:59candles at all.
31:00These supernovae
31:03for theoretical reasons
31:05as well as
31:07through experiments
31:08we know
31:09are quite good
31:11standard candles.
31:12They have always
31:13the same luminosity
31:16at maximum light.
31:18Supernovae are not
31:19all the same brightness.
31:21It seems that
31:221937 C
31:23was one of the most
31:25intrinsically luminous
31:26supernovae ever seen.
31:28If one were to
31:29take the distance
31:30of this nearby supernovae
31:31and compare it
31:32to more distant supernovae
31:33and assume that
31:34they were the same
31:36intrinsically
31:36then one would
31:37overestimate the distance
31:39and hence get
31:40too small a value
31:41of the Hubble constant.
31:43Then this second adjustment
31:44shifts the Hubble constant
31:46further
31:47from something like 65
31:49up to a number
31:50around 80
31:51and now we're
31:52looking at a situation
31:53where there seems
31:54to be no disagreement
31:55at all.
31:56Is a low Hubble
32:00out for the count?
32:02Sandage and Taman
32:03say no.
32:05They claim
32:05that measurements
32:06of new supernovae
32:07reinforce their view
32:09and still give
32:10a low Hubble
32:11and the controversy
32:12is growing.
32:14Recently
32:14physicists from
32:16Femilab
32:16in America
32:17have argued
32:18that the universe
32:18must be at least
32:1920 billion years old
32:21principally
32:22because it fits
32:23its existing theories
32:24better.
32:25Such an age
32:26implies a low Hubble.
32:29On the other hand
32:29Michael Pearce
32:31has just located
32:31the most distant
32:32Cepheid variables
32:33found so far
32:34in the Virgo cluster
32:36of galaxies.
32:37His new estimate
32:38of the constant
32:38has gone up to 90.
32:41A high Hubble
32:42means a young universe
32:43and this is where
32:44the problem lies.
32:47If the Hubble constant
32:48is high
32:49as high as 80
32:50and the density
32:51is high
32:52as high
32:52as what we call
32:54the critical density
32:55that is the density
32:56it takes
32:56to completely
32:57stop the universe
32:59from expanding
32:59then the age
33:01of the universe
33:02might be as low
33:03as 8 billion years.
33:05We know
33:06almost certainly
33:07that there are stars
33:07older than 8 billion years
33:09in our galaxy
33:10and that is a real conflict.
33:13How do we resolve
33:14that conflict?
33:15Well, I'm not sure
33:15how we do that.
33:20The conflict would be resolved
33:26if the oldest stars
33:27were younger.
33:29Is it possible
33:30that we've got
33:30their ages wrong?
33:32How on earth
33:32can you find ways
33:33to measure
33:34how old a star is?
33:37First
33:38is to use
33:40the age
33:41of globular cluster stars
33:43which we believe
33:43are the oldest stars
33:44in our galaxy.
33:46Globular clusters
33:46are tight clusters
33:47of millions of stars
33:48and they were formed
33:50very early
33:50in the history
33:51of our galaxy.
33:52Now the way
33:53we can measure
33:53the age of these
33:54is whether the star
33:56is still burning hydrogen
33:58in the middle.
33:59When a star
34:00finishes burning hydrogen
34:01it changes shape
34:03it starts to grow bigger
34:04it also changes colour
34:05and becomes redder.
34:07And so by studying
34:08in the globular cluster
34:08which kinds of stars
34:10have finished burning hydrogen
34:11we get an age
34:13for the cluster
34:13which is about
34:1514 billion years.
34:16We can determine
34:24the ages
34:25of these stars
34:26not only by studying
34:27star clusters
34:28as we do
34:28for the very
34:29older stars
34:30but also
34:31by looking
34:32at the decay
34:32of radioactive elements
34:33somewhat similar
34:34to the archaeologists
34:36use of carbon-14.
34:40We have better
34:41and better ways
34:42to probe
34:43the interiors
34:44of stars.
34:44One of these
34:45is the new field
34:47of helioseismology
34:48which enables us
34:50to study
34:50the interiors
34:51of the sun
34:52by studying
34:53its oscillation
34:54much in the same way
34:55as a geologist
34:56probes the interior
34:57of the earth
34:58using earthquakes
34:59for example.
35:05Then there's
35:05a third method
35:06which is based
35:08on the fact
35:09that white dwarf stars
35:11which is what
35:12the sun
35:12will end up as.
35:14Because we know
35:15how fast
35:16these stars
35:17cool
35:18we can work out
35:19how old
35:20these white dwarfs
35:21are.
35:25We prefer
35:26a small Hubble constant
35:27because I believe
35:28that at the present time
35:29the ages we get
35:30from the star clusters
35:31are probably
35:33close
35:35to the truth.
35:38There are too
35:39many pieces
35:40of self-consistent
35:42physics.
35:42After all
35:43this is very
35:43mature physics
35:44compared to
35:45what we use
35:47in extragalactic
35:47astronomy usually.
35:49Mature physics
35:50and a consistent
35:51set of answers
35:52suggest that we've
35:53got the ages
35:54of stars
35:54about right
35:55but 14 billion
35:57year old stars
35:58do not belong
35:58in an 8 billion
35:59year old universe
36:00any more than
36:01a granny belongs
36:02in a cot.
36:03Something is wrong
36:04with the whole picture.
36:13Perhaps there is
36:14a way to make
36:15a high Hubble
36:16consistent with
36:17old stars.
36:19There's another
36:19important influence
36:20on the age
36:21of the universe
36:22its density
36:23or how much
36:24stuff or
36:25mass it contains.
36:27Mass causes
36:28gravity
36:28and gravity
36:30affects the
36:30expansion rate
36:31significantly.
36:33When we talk
36:34about the density
36:35of the universe
36:35we're asking
36:36about the total
36:37amount of matter
36:37in it
36:38and matter
36:39is the source
36:40of gravity
36:40it's matter
36:41that causes
36:41gravity
36:42and if you
36:42have more matter
36:43you have more
36:43gravity
36:44so for example
36:45on the moon
36:46the gravity
36:47is less than
36:48is on the earth
36:48because the moon
36:49is only about
36:50an 80th of the
36:50mass of the earth
36:51and that's the
36:52reason that an
36:53astronaut on the moon
36:53can jump much
36:54higher than an
36:55athlete on the
36:55earth
36:55so if you have
36:58more mass
36:59then you have
36:59more gravity
37:00and if the density
37:01of the universe
37:01is higher
37:02then gravity
37:03has a larger
37:03effect on the
37:04evolution of the
37:04universe
37:05and that effect
37:06is to slow down
37:07the expansion.
37:08So the greater
37:09the gravity
37:10the quicker it
37:11slows down
37:11the expansion
37:12or the faster
37:14galaxies need
37:14to have been
37:15moving in the
37:15past to be
37:16slowed to the
37:17speed they're
37:17moving at
37:18today.
37:19It's
37:20counterintuitive
37:21relative, but
37:21more gravity
37:22or stronger
37:23breaks means a
37:24faster expanding
37:25or younger
37:26universe.
37:28Conversely, less
37:30gravity or weaker
37:31breaks means
37:32galaxies would have
37:32been moving more
37:33slowly in the past
37:34to be reduced to the
37:36speed they're moving
37:36at today.
37:38This would take
37:39longer, making the
37:40universe older.
37:41In short, a
37:44high-density
37:44universe is a
37:45young universe
37:46and a low-density
37:47universe is an
37:48old universe.
37:50The important
37:51question then is
37:52how much actual
37:53density is out
37:54there in the
37:54cosmos.
37:56Some of it
37:56obviously is in
37:57the stars.
37:59We think that a
38:00galaxy like our
38:01own contains about
38:03100 billion stars,
38:04roughly like the
38:05sun.
38:06We also think
38:07that inside the
38:08visible universe,
38:09inside this horizon,
38:11there are also
38:11about 100 billion
38:12galaxies.
38:14So there are 100
38:15billion, 100
38:16billion, 10,000
38:18billion, billion
38:19stars in the
38:21visible universe.
38:24The huge number
38:26of stars is dwarfed
38:27only by the huge
38:28amount of space
38:29between them.
38:31The average density
38:32is therefore
38:32extremely low.
38:34It is measured in
38:35terms of what
38:36astronomers call the
38:37critical density,
38:38which is just the
38:39critical amount needed
38:40to halt the
38:41expansion of the
38:42universe.
38:45Now, you can play
38:46games with counting
38:48what you see out
38:48there.
38:49What do you see in
38:50galaxies?
38:50You see only one
38:51one-hundredth of that
38:53critical density in the
38:54bright parts of
38:55galaxies in stars.
38:58You see another
38:58factor of 10 around
39:00galaxies in so-called
39:01dark matter.
39:02This is matter you
39:03have to postulate as
39:04there, not in the
39:05form of stars, to
39:07account for the
39:08motions of galaxies
39:09around each other.
39:11When we go looking for
39:12that mass, when we look
39:13at the stars we know
39:15about, the gas that we
39:16know about, and
39:17everything else we know
39:18about, we can't
39:19account for a
39:20significant amount of
39:21that mass.
39:22So we've had to
39:22postulate something that
39:23we've called dark matter
39:24to explain.
39:25We call it dark matter
39:27because we've never
39:28observed light from it.
39:29But it's worse than that.
39:30We really don't know
39:31what it is.
39:33But of course there
39:33could be lots of dark
39:35matter in other places
39:36where it doesn't cause
39:37such dramatic effects on
39:38nearby galaxies, and we
39:39would never know about
39:39it.
39:40So the problem is to try
39:43and infer how much dark
39:44matter there is in the
39:44universe as a whole,
39:46because that of course is
39:46what determines the
39:47future of the universe,
39:48whether there's enough
39:49dark matter to make
39:50the critical density and
39:50so to make the universe
39:51eventually re-collapse.
39:53We have at least 10% of
39:56this critical mass readily
39:57accounted for in the matter
39:59in and around galaxies.
40:00Where's the other factor
40:01of 10?
40:02Is it even there?
40:04The density of the
40:05universe is quantified
40:08in a number called
40:09omega.
40:10If omega is 1, then there
40:13is enough density in the
40:15universe to resist the
40:16expansion so that you will
40:19just make it off to
40:20infinity.
40:23If the density is higher
40:25so that omega is bigger
40:27than 1, then the
40:29density of the universe is
40:31enough to resist the
40:33expansion and then re-
40:34collapse it.
40:40If the density is smaller,
40:43so omega is less than 1,
40:45then gravity is not enough
40:47to resist the expansion
40:48and the universe will just
40:50fly apart indefinitely.
40:51Today, we do not know the
40:59value of omega very
41:00accurately at all.
41:01We are convinced it's at
41:03least something like a
41:04tenth and some of us think
41:07it could be as large as
41:081.
41:09Well, I think we don't
41:10actually have a good
41:11measurement of the value of
41:12omega today, but many
41:14cosmologists, me included,
41:16I think would believe that
41:18omega is likely to turn out
41:19to be very close to 1.
41:21The universe is on the
41:23edge between expanding
41:24forever and eventually
41:25re-collapsing.
41:29An omega of 1 is
41:31equivalent to a high
41:32density and hence a
41:33young universe.
41:35And the more astronomers
41:36look for missing mass,
41:37the more they find.
41:39And the more astronomers
41:40measure distances, the
41:42higher the Hubble gets.
41:43And the higher the Hubble,
41:44the bigger the trouble.
41:46But if it turns out that
41:49the ages of the stars are
41:51greater than the expansion
41:53time of the universe, as
41:55inferred from the measurement
41:56of the Hubble constant and the
41:58measurement of the density
41:59of the universe, if this
42:01situation arises, then there
42:02is a genuine crisis.
42:04And you have only one option.
42:06You have to drop the basic
42:07assumptions on which your
42:08model of the universe is
42:09based.
42:10In this case, you have to
42:11drop some or perhaps all of
42:14the basic assumptions on
42:15which the Big Bang theory
42:16is based.
42:21So where does this leave
42:23the Big Bang?
42:24Despite the problems, most
42:26cosmologists believe it's
42:28solid.
42:29But there's a certain edginess
42:30among them.
42:31A new generation of
42:32astronomers keep getting
42:34higher values for the Hubble
42:35constant.
42:36And if it keeps going up,
42:38then there really will be big
42:39trouble for the Big Bang.
42:40This is part of the
42:43continuing process of
42:44science.
42:45New observations can
42:47overthrow even the most
42:48well-established theories.
42:50When Edwin Hubble opened his
42:51can of scientific worms 60
42:53years ago, he compelled us to
42:55think again about the nature
42:57of the universe.
42:58He turned common sense on its
43:00head and showed us a strange,
43:03dynamic place shot through with
43:05bizarre concepts.
43:06The weirdest of them all is
43:08the idea that the universe is
43:10actually stretching, that what
43:12we're living in is like a
43:14rubber balloon.
43:16A simple model that works is
43:19to imagine that we live in
43:21two dimensions instead of
43:22three.
43:23Put us on the surface of a
43:25balloon and imagine blowing
43:26up the balloon.
43:27You're sitting on the surface
43:28of the balloon.
43:29You notice neighboring spots in
43:31the balloon are moving away
43:32from you.
43:33You notice that wherever you're
43:34sitting on the surface of that
43:35balloon, you see the same
43:36situation.
43:37You also notice that if you
43:39walked in one direction along
43:41the surface of the balloon,
43:42you'd come right back to where
43:43you started from.
43:44So we'd have a closed space.
43:46It would be finite.
43:48It would be uniform, everywhere
43:49the same.
43:50And if you blow up the balloon,
43:51you'd model the expansion of
43:52our universe.
43:55But the real universe is not
43:57like that.
43:58The Big Bang Theory tells us
44:00that all matter was created at
44:01once.
44:02There is no more air to blow
44:04into the balloon.
44:04There is no hole in the universe
44:07through which more material can
44:08be added.
44:10How can we make sense of
44:11something of fixed size which
44:13keeps getting bigger?
44:15We need to dig deeper into
44:16apparently straightforward ideas
44:18such as here and now.
44:22When you look out into the night
44:23sky and you see the stars far
44:25away, you're seeing them because
44:27of the light that has traveled
44:29from them to you.
44:30Now it takes time for light to
44:33travel here.
44:34So what you're doing is seeing
44:36the stars as they were in the
44:38past, the amount of time it's
44:39taken for the light to reach us.
44:41And the further and further away
44:42those stars are, the further back
44:44in time you're looking.
44:47Now we're seeing a star, let's say
44:496,000 years ago.
44:51Imagine somebody on that star
44:53looking at us.
44:54They would be seeing us as we
44:57were 6,000 years ago.
45:00Which of those two is now?
45:03So you begin to see that the
45:05idea of now becomes a little bit
45:08less clear than it was perhaps a
45:09moment ago, if that's the right
45:11phrase to use.
45:12So space and time are linked
45:14together.
45:15As we are looking across space,
45:17we are looking back in time.
45:18Albert Einstein was the first
45:23person to recognize this profound
45:25connection between space and time
45:27and the paradoxes that came with
45:29it.
45:30Einstein realized that the only way
45:31out was if the speed of light was
45:34the same, no matter how you looked
45:35at it.
45:39When the Earth's going that way
45:40around the sun in January, you
45:42measure the speed of light, it's
45:44exactly the same as six months
45:46later when you're going that way
45:47around the sun.
45:49Now that is a very surprising
45:51concept because you're used to the
45:53idea that if a car goes past you
45:55that way when you're running along,
45:58if it comes back a few minutes
45:59later going that way, your relative
46:02speed will differ.
46:03In the case of light, it's not
46:04like that.
46:08If the speed of light is constant
46:10and not variable, then we have a
46:12bizarre result.
46:13Space and time must be variable
46:15and not constant.
46:17A mile is not necessarily a mile.
46:20A minute is not necessarily a
46:21minute.
46:23Such flexibility or relativity
46:25only becomes apparent when objects
46:27move at near the speed of light.
46:30Astronomically speaking, the
46:31expanding universe of Edwin Hubble
46:33can actually stretch.
46:35to the extent that experiments come
46:40out right when we use Einstein's
46:43equation of relativity, we believe
46:45that his ideas are indeed the best
46:49description we have of the universe
46:51as we perceive it.
46:54The flexibility of space was first
46:56proved in 1919 when light rays were
46:59found to bend around the sun during a
47:02solar eclipse.
47:04The rays themselves didn't bend, but
47:06the space through which they
47:07travelled did, distorted by the
47:09force of gravity.
47:11The flexibility of time has been
47:13proved.
47:14Atomic clocks in high-speed
47:16aeroplanes run slower than those
47:18on the ground.
47:23An elastic Hubble universe has a
47:25dramatic consequence.
47:27If time and space are flexible,
47:29then there could have been moments
47:31when they didn't exist at all.
47:33No time and no space.
47:38Given that space and time are so
47:39closely related to one another,
47:42asking the question of what was
47:44there before the universe is
47:46exactly the same as asking what is
47:47there outside the universe.
47:49There's no difference.
47:50They're exactly the same question.
47:52And the answer is the same.
47:54Space was created with the universe.
47:56Time was created with the universe.
47:57Time is a concept that is part of a
48:00universe.
48:01It did not exist before the universe
48:02came into existence.
48:05The idea that time and space were
48:07created, as opposed to always being
48:09there, is extremely hard to come to
48:11terms with.
48:13One way to envisage the flexibility
48:15of space is to imagine the end of
48:18everything.
48:19A universe which eventually stops
48:21expanding and starts to contract.
48:24The galaxies which before were flying
48:28apart will now begin to fly together.
48:33The whole material content of the
48:35universe will come closer and closer
48:38together.
48:39So the material that occupy the entire
48:42volume of space will still occupy the
48:44entire volume of space.
48:46But this will now be much denser and a
48:48much smaller region.
48:50It would become as small as a galaxy, as
48:53small as a star, as small as an orange.
48:58So all of space will eventually be
49:00contained in the science of the orange.
49:05So where is this orange?
49:07The orange, or the universe, is in fact
49:17situated nowhere and no when, for there is
49:21neither space nor time left for it to
49:23exist in.
49:25This is difficult to grasp, as are ideas
49:28such as there being no edge to the
49:30universe, or even the universe emerging
49:32from nothing, or even a rubber universe
49:34which expands, the legacy of a boxer
49:37called Edwin Powell Hubble.
49:39This doesn't mean that these ideas are
49:41wrong, just that they are hard to
49:43understand with our limited
49:45consciousness.
49:47Perhaps what we need is a bigger
49:49consciousness.
49:49For the fact sheet that accompanies this
50:05programme, please send a cheque or postal
50:07order for £2.50 payable to Channel 4, 2
50:10Big Bang, PO Box 4000, London W3 6XJ.
50:15A handful of submarines found, could you
50:30go over to the world?
50:31Is this supposed to be triggered from the
50:32alphabet?
50:34Yes, it is!
50:36Weird.
50:36A handful of submarines fed about.
Be the first to comment
Add your comment