Presentation on theme: "Few theories are so widely known by the public as the ‘Big Bang’ origin of the Universe. For GCSE science in the UK, you need to understand the evidence."— Presentation transcript:
Few theories are so widely known by the public as the ‘Big Bang’ origin of the Universe. For GCSE science in the UK, you need to understand the evidence for this theory.
The theory states that about 13 billion years ago, the Universe expanded at a stupendous rate from being very small to very large.
So, what is the evidence for the theory and what research is going on to develop it? Make a short note about each piece of evidence
EvidenceDateInterpretation Try making a table like this
At the beginning of the 20 th Century, most scientists thought that the Universe had existed for ever. In 1905 Einstein created equations that explained the nature of time and space. However they predicted an expanding Universe. Convinced of un unchanging Universe, Einstein changed his equations. He later described this unscientific behaviour as “my biggest blunder”.
EvidenceDateInterpretation Einstein makes equations that explain time and space 1905They predict an expanding Universe You should have noted something like this:
The Big Problem Space is Big I mean really big It took a long time to realise exactly how really big it is Measuring how far away things are is difficult The first person to find a method to measure things on the galactic scale was an American woman
We have speeded up time so that one second is a day Can you see an odd star?
Henrietta Leavitt Henrietta Leavitt was very interested in this type of star, called a Cepheid variable. In 1912 she carefully measured the brightness and period of hundreds of them in the Small Megellanic Cloud; a satellite galaxy to the Milky Way. Leavitt wanted to know if there was a relationship between the brightness of the stars and how fast they pulsed. Nobody knew how far away the cloud was but Leavitt reasoned that as the cloud was a long way off, all the stars in the cloud would be roughly the same distance away.
MagnitudePeriod (days) Leavitt measured the brightness and period of hundreds of Cepheid variables. Here is a sample of her data Just to be awkward, astronomers measure brightness in a scale called magnitude, where the smaller the magnitude, the brighter the object. What do you think the relationship is between brightness and period?
This is what her data actually looked like. Is there a relationship between 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?
The brighter the star, the shorter its period. There is a strong correlation The data is spread out indicating other variables are having an effect. Later it was found that there are several types of Cepheid variables.
Leavitt had discovered that the brightness of one type, Cepheid variables, was linked to their pulsation period.
In 1666, Isaac Newton discovered a basic relationship about brightness; something twice as far away is a quarter as bright. This is called the inverse square rule. When Leavitt combined this fact with he discovery about Cepheids she had created a tool for estimating the relative distance of objects. This tool was key to studying the Universe. Her achievement was recognised by naming a crater on the Moon in her honour.
A Cepheid with a period of 2 days in the Andromeda Galaxy is 100 times dimmer than a Cepheid with the same period in the Small Megellanic Cloud How much further away is the Andromeda Galaxy compared to the Small Megellanic Cloud? Image T.A.Rector and B.A.Wolpa/NOAO/AURA/NSF
A year later in 1913, Danish astronomer Ejnar Hertzsprung measured the distance to ‘nearby’ Cepheid variables. He needed to look at a Cepheid in relation to very distant background stars from two different vantage points. He could then measure the shift of the star against the background and calculate its distance.
The solar system is hurtling through interstellar space at a rate of 15km per second in the direction of the constellation Hercules. At that rate we cover 300 million km in about eight months. By looking at the positions of Cepheid's on photographic plates taken several years apart, Hertzsprung was able to detect and measure a shift for 13 stars. With this, the SMC was placed at approximate 200,000 light years distant – twice the diameter of the Milky Way.
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
In 1923, American astronomer Edwin Hubble used the 100 inch diameter telescope on Mount Wilson in California to see if there were any Cepheid's in Andromeda. He found them but they were far fainter than he expected. He calculated that it was at least a million light years distant.
Where are we? So we now have a method of finding out how far away things are. The next chapter in the story of the Big Bang is about working out the relative velocity of things.
In 1802 the Englishman William Hyde Wollaston noticed dark lines in the Sun’s spectrum. In 1814 the German Joseph Von Fraunhofer recognised that these lines were missing wavelengths. In 1857 two friends in Germany, Robert Bunsen and Gustav Kirchhoff discovered that the missing wavelengths were the light fingerprints of different elements which they were able to identify. You still use one of the bits of equipment Bunsen invented to do this – his Burner! Fingerprints of light
If your school has some spectrometers, see if you can identify some elements in Sun light Here you can see HRH the Prince of Wales using a simple spectrometer to identify elements in the Sun. You don’t even need a sunny day.
In 1872 Annie Jump Cannon, at Harvard University, lead a team that analysed the spectra of 250,000 stars. She developed the basis for the star classification system that we still use today. O B A F G K M. Generations of astronomers have learnt this sequence with the pneumonic 'Oh, be a fine girl (guy), kiss me!'
Here is the spectrum of Cannon’s seven classes of star. A few of the most important fingerprint absorption lines are labelled. From the information in the chart, can you explain the differences between star types? O B A F G K M Fe He H Na Ca 35,000 K 22,000 K 11,000 K 7,000 K 6,000 K 5,000 K 4,000 K Surface Temperature Class
There are two main difference; the colour spread and the lines. As things get hotter, they go from red hot, through orange, yellow white and blue. M will appear as reddish stars and O as bluish. Our own star is in the G class, and viewed from far off, would appear as a yellow star. The lines differ only in whether they are there or not. They do not change position. Eg the Iron (Fe) line appears at the same point in every spectrum. O B A F G K M Fe He H Na Ca 35,000 K 22,000 K 11,000 K 7,000 K 6,000 K 5,000 K 4,000 K Surface Temperature Class
Map the temperature of the Sun with Cambridge University SOHO researcher Helen Mason. SOS website challenge
Where are we? We now know that when a star gives off light. the spectrum is ‘bar-coded’ with a series of absorption lines. Elements create these lines at specific wavelengths. If something changes that wavelength, we’ll be able to detect it.
Have you ever noticed that the noise of a passing motor vehicle, train or plane changes in pitch? Have a listen (if you can’t hear anything, switch the speakers on!) They make a sort of “neeow” sound.
Christian Doppler The first person to explain this effect was the Austrian maths teacher Christian Doppler in We now call it the Doppler effect. He followed up his idea with experiments involving putting musicians on open railway carts with another musician on the station platform. The musicians could compare notes played to notes heard.
Christian Doppler Doppler showed that the effect was the same regardless of whether the note was played on the moving train or the platform. It was all to do with relative movement. Goodness knows what the train travelling public thought of these experiments!
What Doppler said was that waves travel at a particular speed so they cannot move away from the object any faster or slower.
So when sound waves are given off in the same direction as the object is moving, they get bunched up. This makes them a shorter wavelength and a higher frequency. Those given off behind get spread out. This makes them have a longer wavelength and a lower frequency.
Doppler realised that this should also effect light waves. He said that if the object is coming towards you and making sound, the pitch will be higher. If it's making light the colour will be bluer. If the object is going away from you and making sound the pitch will be lower. If it's making light its colour will be redder. Doppler hoped to use this method to detect the orbiting of double stars around each other but his measuring techniques were not up to the task.
You don't notice a colour change because the change is so tiny on something going a million times faster than sound. However the fingerprints of a star’s elements should also be shifted towards the red or blue end of the spectrum and this is measurable.
In 1913 Vesto Slipher found that the Andromeda galaxy is blue shifted. It and the Milky way are rushing towards each other at 300km per second. At the time Slipher did not know how far apart the galaxies are. You do. How long have we got until they collided? – take a class vote. Distance 20 billion billion km Closing velocity 10 billion km/year A 20 million years B 2 billion years C 20 billion years D 2 million years
B 2 billion years
Whilst Slipher found Andromeda was blue shifted, most of the other galaxies were red shifted. What was his conclusion about the movement of galaxies relative to the Milky way?
Most galaxies are moving away from the Milky way! This is peculiar – what’s wrong with us? It makes us appear to be at the centre of the Universe. It could be evidence for the creation of the Universe – was it created here in a big explosion?
Where are we? Using Cepheid variables, we can now roughly measure how far away a galaxy is. Using the redshift of absorption lines, we can quite accurately measure how fast a galaxy appears to be moving away from us.
We now go back to Edwin Hubble on Mount Wilson. It is now 1929 and Hubble is doing a survey to find out if there is a relationship between how far away a galaxy is and how fast it is hurtling away from us. If we really are at the centre of an explosion, all the galaxies should be going away from us at the same velocity.
Distance (Mega parsecs)Velocity (km/s) 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
Here is the complete set of Hubble’s data. It is even worse than the five data points 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 distance measurements, he thought the galaxies were ten times closer than they really were. However that does not change the fact that there is a relationship.
What is the explanation for the relationship? The Universe could not have started with an explosive event where we are in space. If that had happened, all the galaxies would be rushing away from us at the same velocity. To explain increasing velocity, we need another model.
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 up for us What do you think will happen?
Imagine the Universe as a balloon The galaxies stay the same size but the distances between them open up as the rubber separating the expands Imagine that one of the galaxies is you in the Milky Way. What would the movement of the other galaxies look like to you?
Milky Way Closer galaxy Further galaxy The further away the galaxy, the faster it appears to be moving away. Why does this happen?
Milky Way Closer galaxy Further galaxy There is more expanding space/rubber between more distant galaxies.
Redshift is worked out using this formula: observed wavelength minus the original wavelength divided by the original wavelength. So in this spectrum from a galaxy, the Calcium II K line, which is usually at nm (in the far blue region of the spectrum) is observed at double that at (into the infrared part of the spectrum) the redshift (z) = /393.4 = nm Ca 2+ K
The resulting redshift scale is logarithmic so that the difference between redshift 1 and 2 is billions of years whilst between 7 and 8, only a couple of hundreds of thousands of years. Whilst redshift 7 puts a galaxy at 800 thousand years after the big bang, redshift 12 puts it at only 400 thousand years.
How far back in time are we observing that galaxy that we calculated was at redshift 1?
7 billion year ago
The explanation for an expanding Universe is that if you play it backwards, you start of with all the Universe in the same place in the past. In effect you have a creation event for the Universe. This idea of an expanding Universe from a creation event, was ridiculous to some scientists. One of its greatest critic was an English scientists called Fred Hoyle. In the 1950’s, just to show how daft the idea was, he called it the “Big Bang”. Everyone else thought that was a great name and we have used it ever since.
Its important to understand that as the Universe expands, it is not pushing 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 of the balloon. The paper galaxies fly apart because the rubber space is expanding. So the distant galaxies are not flying away through space like the Andromeda galaxy is flying towards us. Instead they are relatively stationary but are being carried away by the expanding space between us.
In 1996 the HST took this image of an area in Ursa Major (the Plough/Big Dipper) From their redshifts, the furthest galaxies recorded here are thought to be about a billion years old
In 2003 the HST took this image of an area in the constellation Fornax with a more sensitive detector From their redshifts, the furthest galaxies recorded here are thought to be about 400 thousand years old
In 2003 the HST took this image of an area in the constellation Fornax with a more sensitive detector Search for the furthest galaxy in this image with ESA scientist Nino Panagea. SOS website challenge
But what about the Big Bang itself, can we see that? In the early 1960s several groups worked out how hot the Big Bang would be when the Universe cleared and light 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 redshifted that it would be in the microwave part of the spectrum. As you probably know, this is the part of the spectrum your mobile phone uses. Only two people in the world were usiing a receiver that could find this signal from the beginning of time – and they had their own problems.
In 1963 Arno Penzias and Robert Wilson were trying to get rid of interference in their satellite radio receiver. Whichever direction in the sky they pointed, they got the interference. They tried everything. Finally they decided that it was the heat generated by pigeon droppings inside their 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 radiation! Eventually they realised what they had found and were given Nobel prizes for their discovery. Today space telescopes are able to form images using the microwave background and see the Universe as a baby.
Taken by NASA's Wilkinson Microwave Anisotropy Probe (WMAP), the patterns of intensity show the ‘wrinkles’ that resulted in concentrations of matter and eventually galaxy clusters. Baby picture of the Universe
This is as far back as we can see. The microwave background forms a wall at about 300 thousand years after the big bang. This is because it was at this time that the Universe was cool enough for atoms to form. Before that time, the hot particle 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!
The following graphic sums up how HST and WMAP have peered back into the past to reveal the origin and evolution of the Universe. The next generation of space and ground based telescopes will be able to look in even grater detail and fill in the history between the microwave background and the first galaxies.
The findings of space telescopes and other instruments can be added together to trace the history of the Universe. How can we go back before the microwave background data?
If you want to study the Big Bang before 300,000 years after it happened, you have to recreate it in the laboratory – and that’s a bit tricky!
Scientists use giant ‘Atom Smashers’ like this one at the Centre Européen pour la Recherche Nucleaire (CERN) which spans the border between Switzerland and France. Here electromagnets are used to accelerate particles in either direction around a huge track and then let them experience a head on crash. Image CERN
Particles spay out of Big Bang temperatures created by the collision of accelerated particles in CERN’s particle accelerator. Image CERN
The energies that the particles have when they collide have not existed since the Big Bang. In recreating the temperatures of the Big Bang, the results of the smashes take the history of the Universe further back than the wall of microwaves when the Universe was 300,000 years (10 13 seconds) old. Image CERN
Scientists can use their models of the Big Bang to predict the results of collisions at temperatures which are the same that would have existed at different times after the Big Bang. Image CERN
A prediction of what the next generation of atom smasher should produce if scientists ideas about the first moments of the Big Bang are correct. Image CERN
Credits Written by Michael Cripps, Neatherd High School Norfolk UK Website by Michael Cripps and Graham Colman of Taverham High School, Norfolk UK 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 Education Business 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, Goddard Space Flight Centre and other institutions worldwide. Special thanks to Helen Mason at Cambridge University and Dennis Christopher at NASA, GSFC. This resource and its content may be used freely for non commercial educational purposes.