big bang lessonfvs

8/13/2019 Big Bang Lessonfvs

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http://www.nasa.gov/http://www.norfolk-exchange.org.uk/content/default.asphttp://www.esa.int/esaCP/index.htmlhttp://www.neatherd.org/astronomy/SOS/SOShome.htm


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Few theories are so widely knownby the public as the Big Bang

origin of the Universe.

For GCSE science in the UK, youneed to understand the evidencefor this theory.
http://www.neatherd.org/astronomy/SOS/SOShome.htm


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The theory statesthat about 13 billion

years ago, theUniverse expanded

at a stupendousrate from being

very small to very

large.


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So, what is the evidence for thetheory and what research is goingon to develop it?

Make a short note about eachpiece of evidence


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Evidence Date Interpretation

Try making a table like this


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At the beginning of the 20 th Century, most scientists thoughtthat the Universe had existed for

ever.In 1905 Einstein created

equations that explained thenature of time and space.

However they predicted anexpanding Universe .Convinced of un unchangingUniverse, Einstein changed his

equations.He later described this

unscientific behaviour as mybiggest blunder.


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Evidence Date Interpretation

Einstein makes

equations that explaintime and space

1905 They predict an

expanding Universe

You should have noted somethinglike this:


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We have speeded up time so that one second isa day

Can you see an odd star?


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Henrietta LeavittHenrietta Leavitt was very interested in thistype of star, called a Cepheid variable. In1912 she carefully measured the brightnessand period of hundreds of them in the SmallMegellanic Cloud; a satellite galaxy to the

Milky Way.Leavitt wanted to know if there was arelationship between the brightness of thestars and how fast they pulsed.

Nobody knew how far away the cloud wasbut Leavitt reasoned that as the cloud was along way off, all the stars in the cloud wouldbe roughly the same distance away.


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Magnitude Period (days)6 925 504 83 42 2

Leavitt measured the brightness and periodof hundreds of Cepheid variables. Here is

a sample of her data

Just to be awkward, astronomers measure brightness in a scalecalled magnitude, where the smaller the magnitude, the brighterthe object.

What do you think the relationship is between brightness andperiod?


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This is what her data actually looked like. Is there a relationshipbetween the brightness of the star and the period of its pulsing?

How sure are you of your conclusion?

Why could the data be so spread out from the line of best fit?


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Leavitt had discovered that the brightness ofone type, Cepheid variables, was linked totheir pulsation period.


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In 1666, Isaac Newton discovered a basicrelationship about brightness; something twiceas far away is a quarter as bright. This is calledthe inverse square rule.

When Leavitt combined this fact with hediscovery about Cepheids she had created atool for estimating the relative distance ofobjects.

This tool was key to studying the Universe.Her achievement was recognised by naming a

crater on the Moon in her honour.


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A Cepheid with aperiod of 2 days inthe AndromedaGalaxy is 100 timesdimmer than aCepheid with thesame period in theSmall MegellanicCloud

How much further

away is the Andromeda Galaxycompared to theSmall MegellanicCloud?

Image T.A.Rector and B.A.Wolpa/NOAO/AURA/NSF


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A year later in 1913, Danishastronomer EjnarHertzsprung measured thedistance to nearbyCepheid variables.

He needed to look at aCepheid in relation to verydistant background starsfrom two different vantagepoints. He could thenmeasure the shift of the staragainst the background andcalculate its distance.


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The solar system is hurtlingthrough interstellar space at arate of 15km per second in the

direction of the constellationHercules. At that rate we cover300 million km in about eightmonths.

By looking at the positions ofCepheid's on photographicplates taken several yearsapart, Hertzsprung was able to

detect and measure a shift for13 stars. With this, the SMCwas placed at approximate200,000 light years distant twice the diameter of the MilkyWay.

F l h f i th


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For example, how far away is the Andromeda Galaxy?

Approximately 2 million light years

However in 1913 most astronomers thought that

Andromeda was just a cloud of gas in our galaxy


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In 1923, Americanastronomer EdwinHubble used the 100inch diametertelescope on MountWilson in California to

see if there were anyCepheid's in Andromeda. Hefound them but they

were far fainter thanhe expected.

He calculated that itwas at least a millionlight years distant.


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Where are we?

So we now have a method of finding outhow far away things are.

The next chapter in the story of the BigBang is about working out the relativevelocity of things.


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In 1802 the Englishman William HydeWollaston noticed dark lines in theSun s spectrum.

In 1814 the German Joseph VonFraunhofer recognised that these

lines were missing wavelengths.In 1857 two friends in Germany,Robert Bunsen and GustavKirchhoff discovered that themissing wavelengths were the light

fingerprints of different elementswhich they were able to identify.You still use one of the bits of

equipment Bunsen invented to dothis his Burner!

Fingerprints of light


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If your school has somespectrometers, see if you can

identify some elements in Sun light

Here you can seeHRH the Prince ofWales using a simplespectrometer toidentify elements inthe Sun.

You don t even needa sunny day.


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In 1872 Annie Jump Cannon, at Harvard University, leada team that analysed the spectra of 250,000 stars.

She developed the basis for the star classification systemthat we still use today. O B A F G K M .

Generations of astronomers have learnt this sequence withthe pneumonic 'Oh, be a fine girl (guy), kiss me!'


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Here is the spectrum of Cannon s seven classes of star. A few of themost important fingerprint absorption lines are labelled. From theinformation in the chart, can you explain the differences between startypes?

O

B

A

F

G

K

M

Fe He H

NaCa

35,000 K

22,000 K

11,000 K

7,000 K

6,000 K

5,000 K

4,000 K

SurfaceTemperatureClass


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Map the temperatureof the Sun withCambridge University

SOHO researcherHelen Mason.

SOS website challenge


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Where are we?

We now know that when a star gives offlight. the spectrum is bar -coded with aseries of absorption lines.

Elements create these lines at specificwavelengths.

If something changes that wavelength,we ll be able to detect it.


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Have you ever noticed that the noise of apassing motor vehicle, train or planechanges in pitch?

Have a listen (if you can t hear anything,switch the speakers on!)

They make a sort of neeow sound.


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Christian Doppler

The first person to explain this effectwas the Austrian maths teacherChristian Doppler in 1842. We

now call it the Doppler effect. Hefollowed up his idea withexperiments involving puttingmusicians on open railway carts

with another musician on thestation platform. The musicianscould compare notes played tonotes heard.


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Christian Doppler

Doppler showed that the effectwas the same regardless ofwhether the note was playedon the moving train or theplatform. It was all to do withrelativemovement. Goodness knowswhat the train travelling publicthought of these experiments!


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What Doppler said was that waves travel at aparticular speed so they cannot move away

from the object any faster or slower.


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Doppler realised that this should also effect lightwaves.

He said that if the object is coming towards youand making sound, the pitch will be higher. If it'smaking light the colour will be bluer.

If the object is going away from you and makingsound the pitch will be lower. If it's making lightits colour will be redder.

Doppler hoped to use this method to detect theorbiting of double stars around each other buthis measuring techniques were not up to thetask.


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You don't notice a colour change becausethe change is so tiny on something going amillion times faster than sound.

However the fingerprints of a star s elementsshould also be shifted towards the red orblue end of the spectrum and this ismeasurable.


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B 2 billion years


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Whilst Slipher found Andromeda was blueshifted, most of the other galaxies werered shifted.

What was his conclusion about themovement of galaxies relative to the Milkyway?


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Most galaxies are moving away from theMilky way!

This is peculiar what s wrong with us?

It makes us appear to be at the centre of theUniverse.

It could be evidence for the creation of theUniverse was it created here in a bigexplosion?


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Where are we?

Using Cepheid variables, we can nowroughly measure how far away a galaxy is.

Using the redshift of absorption lines, wecan quite accurately measure how fast agalaxy appears to be moving away fromus.


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Here is some of Hubble s data


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Distance (Mega parsecs) Velocity (km/s)

0.2 1000.5 400

1 800

1.5 750

2 1200

Make a quick sketch graph of this data

What is the relationship between distance and velocity

How confident are you of the relationship?

(a Mega parsec is roughly 3 million light years)

Here is some of Hubble s data


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Here is the complete set of Hubble s data. It is even worse than the five datapoints you used. However there is a significant relationship.

The further away, the faster the galaxy is going away from us.

Because Hubble mistook clouds of stars for individual stars in his distancemeasurements, he thought the galaxies were ten times closer than theyreally were. However that does not change the fact that there is arelationship.


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What is the explanation for therelationship?

The Universe could not have started withan explosive event where we are in space.If that had happened, all the galaxieswould be rushing away from us at thesame velocity.

To explain increasing velocity, we need

another model.


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Imagine the Universe as a balloon

Stick some bits of white paper on it.These represent galaxies.

We ll ask Edwin Hubble to blow it upfor us

What do you think will happen?


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Imagine the Universe as a balloon

The galaxies stay the samesize but the distancesbetween them open up as therubber separating theexpands

Imagine that one of thegalaxies is you in the Milky

Way.What would the movement ofthe other galaxies look like toyou?

The further away the galaxy, the faster it appears to be


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MilkyWay

Closer

galaxy

Furthergalaxy

y g y, ppmoving away.

Why does this happen?


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Redshift is worked out using this formula: observed wavelengthminus the original wavelength divided by the originalwavelength. So in this spectrum from a galaxy, the Calcium II Kline, which is usually at 393.4 nm (in the far blue region of thespectrum) is observed at double that at 786.8 (into the infraredpart of the spectrum) the redshift (z) = 786.8-393.4/393.4 = 1

786.8nm

Ca 2+ K


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The resulting redshift scale is logarithmic so that the difference between redshift 1and 2 is billions of years whilst between 7 and 8, only a couple of hundreds ofthousands of years . Whilst redshift 7 puts a galaxy at 800 thousand years after thebig bang, redshift 12 puts it at only 400 thousand years.


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How far back in time are weobserving that galaxy that wecalculated was at redshift 1?


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7 billion year ago

The explanation for an expanding


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Universe is that if you play itbackwards, you start of with all theUniverse in the same place in the past.

In effect you have a creation event forthe Universe.

This idea of an expanding Universefrom a creation event, was ridiculous tosome scientists.

One of its greatest critic was anEnglish scientists called Fred Hoyle. Inthe 1950 s, just to show how daft theidea was, he called it the Big Bang.Everyone else thought that was a greatname and we have used it ever since.


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Its important to understand that as the Universe expands, it is notpushing out into space, but creating space.

This is a bit tricky to get your head around.

Think about the balloon model. The space here is the rubber ofthe balloon. The paper galaxies fly apart because the rubberspace is expanding.

So the distant galaxies are not flying away through space like the Andromeda galaxy is flying towards us. Instead they arerelatively stationary but are being carried away by the expandingspace between us.


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In 2003 the HST took this image of an area in the


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In 2003 the HST took this image of an area in theconstellation Fornax with a more sensitive detector

From their redshifts, the furthestgalaxies recorded here arethought to be about 400thousand years old

In 2003 the HST took this image of an area in the


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In 2003 the HST took this image of an area in theconstellation Fornax with a more sensitive detector

Search for the furthest galaxyin this image with ESAscientist Nino Panagea.

SOS website challenge


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But what about the Big Bang itself, can we see that?

In the early 1960s several groups worked out how hotthe Big Bang would be when the Universe cleared andlight could travel through space.

They then worked out that a view of the Universe at a

distance of 13 billion light years would be so redshiftedthat it would be in the microwave part of the spectrum. As you probably know, this is the part of the spectrumyour mobile phone uses.

Only two people in the world were using a receiver thatcould find this signal from the beginning of time andthey had their own problems.

Pi P


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In 1963 Arno Penzias and Robert Wilson were trying to get rid of interference intheir satellite radio receiver. Whichever direction in the sky they pointed, theygot the interference. They tried everything.

Finally they decided that it was the heat generated by pigeon droppings insidetheir antenna. So they got out buckets and scrubbing brushes and cleaned out

the poo. This had absolutely no effect. What had they found?

Pigeon Poo

The Big Bang microwave background


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The Big Bang microwave backgroundradiation!

Eventually they realised what they hadfound and were given Nobel prizes for

their discovery.

Today space telescopes are able to form

images using the microwave backgroundand see the Universe as a baby.

Baby picture


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Taken by NASA'sWilkinson Microwave

Anisotropy Probe(WMAP), the patterns ofintensity show thewrinkles that resulted inconcentrations of matterand eventually galaxyclusters.

Baby pictureof theUniverse

Soup makes astronomers blind!


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This is as far back as we can see. The microwave background forms a wall atabout 300 thousand years after the big bang. This is because it was at this timethat the Universe was cool enough for atoms to form. Before that time, the hotparticle soup that made up the Universe also made the Universe opaque to light.

All the information from that period was absorbed by the soup.

Soup makes astronomers blind!


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The following graphic sums up how HSTand WMAP have peered back into thepast to reveal the origin and evolution of

the Universe.The next generation of space and groundbased telescopes will be able to look ineven grater detail and fill in the historybetween the microwave background andthe first galaxies.


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The findings of space


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g ptelescopes and otherinstruments can be addedtogether to trace thehistory of the Universe.

How can we go backbefore the microwavebackground data?


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If you want to study the Big Bang

before 300,000 years after ithappened, you have to recreate itin the laboratory and that s a bit

tricky!


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Particles spay out of Big Bang temperatures created by the collision ofaccelerated particles in CERN s particle accelerator.

Image CERN


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The energies that theparticles have when theycollide have not existedsince the Big Bang.In recreating thetemperatures of the BigBang, the results of thesmashes take thehistory of the Universefurther back than thewall of microwaves

when the Universe was300,000 years (10 13

seconds) old.

Image CERN


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Scientists canuse their modelsof the Big Bang topredict the resultsof collisions attemperatureswhich are the

same that wouldhave existed atdifferent timesafter the BigBang.

Image CERN


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A prediction of what the next generation of atom smashershould produce if scientists ideas about the first momentsof the Big Bang are correct.

Image CERN

Credits


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Written by Michael Cripps, Neatherd High School Norfolk UK

Website by Michael Cripps and Graham Colman of Taverham High School, NorfolkUK

Images and graphics by Michael Cripps, ESA, NASA and CERN

Space Telescopes in School project sponsored by the UK Particle Physics and

Astronomy Research Council, the European Space Agency and Norfolk EducationBusiness Exchange

Our Star sponsored by the Royal Society

Technical assistance by the scientists, engineers and educationalists of the European

Space Agency and NASA at the Space Telescope Science Institute, GoddardSpace Flight Centre and other institutions worldwide.

Special thanks to Helen Mason at Cambridge University and Dennis Christopher atNASA, GSFC.

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