A Blog for the Curious and the Scientifically Perplexed

This is the story of a great journey that started with a great thought. One day in 1895 a boy looked into a mirror and wondered what the universe would look like if he could travel on a beam of light. That sixteen year old boy was Albert Einstein and that one thought started him on the road to discover his Theory of Relativity. The great man has been reinvented as Albert 2.0 to come back and blog about a journey through space on a beam of light and explain the science behind everything from atoms, blackholes to global warming. If you've just joined and want to start at the beginning use the index on the left. If you're bored try these links below just for fun.


Sunday, May 13, 2007

Fire Engines, Microwaves and Eggs

"Albert, how can you tell the universe is expanding? It’s far too big to see the edges."

Because wherever you look, everything is moving away from each other.

"Yes, but how do they know that?"

In the same way that a blind man can tell whether a fire engine is coming towards him or travelling away from him. The siren from a fire engine that's travelling towards you is slightly higher pitched than the sound of the same siren when it's travelling away from you. An effect that Christian Doppler will discover in Vienna in 1842 towards the end of our journey and is still named after him as the Doppler Effect. It was easy to demonstrate the effect with sound in 1842, but Doppler also predicted that the same principle could apply to light coming from a stars. Rather than becoming lower pitched when moving away, the light is shifted very slightly in colour becoming a little more red. The faster the movement, the bigger the shift. The effect that Doppler predicted in stars is called the Red Shift and was discovered by Edwin Hubble in 1929. From looking at light from distant galaxies it seems that all the galaxies are moving apart. The further away a galaxy is, the faster it seems to be moving.

"So why don't fire engines look redder when they are going away from you."

The Doppler Effect only works with the sirens of fire engines because fire engines can travel at a reasonable fraction of the speed of sound. The speed of sound is only 760 miles per hour. Light travels almost a million times faster at 670 million miles per hour and so a fire engine would have to be going a million times faster than normal to be 'red shifted' in the s
ame way that the siren changes pitch. Galaxies are a lot faster than fire engines and can travel at millions of miles per hour and so that's why their light appears slightly redder than it is.

“So what made scientists believe in the Big Bang?”

One by one, scientists came around to the idea as more clues were found. You know you asked about hearing the Big Bang? Well there are still echoes of the Big Bang out there in the universe, not in the form of sound waves but as faint ripples of microwave signals coming from space.

“Hold on Albert, you’re losing me here. Microwave ovens in space? Poets and priests? Are you sure they put you back together right when they put in this computer?”

I’ve never felt better and trust me this is all true. Microwaves are more than just white boxes to heat food. Microwave ovens are named after the wave, and microwaves are like a small radio wave. Luckily these microwaves from space are so faint that there is no risk of you being cooked, but the pattern of these faint signals gives clues about the start of the universe. This is how science works, you first have theory and idea and then you have to find clues or evidence that support it or disprove it. The Big Bang theory predicted three things. That the universe is expanding. That is should mostly be made of hydrogen and the heat of the explosion should be still detectable as faint traces of microwaves. The first two are true, so if you can find the microwaves and there is no other good explanation for them then your theory is probably correct.

"How long ago was this?"

Like I said before, about 14 billion years ago.

"And there are still microwaves echoing around? I can't believe that."

OK, I admit it's like trying to work out the shape of a stone thrown into a pond fourteen billion years ago by looking at the ripples left. But the ripples are very small and the Big Bang was the biggest splash of all time.

“Is that why you said you were so impressed with the microwave oven back at the start of the journey?”

Of course, isn’t it amazing that the same principle can tell you about how the universe begain and cook popcorn without any obvious source of heat?

“So how does a microwave oven work?”

A microwave is part-way between light and a radio wave. Light can't get through a piece of chicken at all. But a radio wave can pass straight through a chicken and carry on half way around the world. Microwaves are in the middle, they can get most of the way through a chicken but a lot of them will be absorbed. When absorbed they give up their energy and so heat up the food from inside. But there’s another reason why I like a microwaves. The fact they can heat things up was accidentally discovered by Percy Spencer in 1946 when he was experimenting with something called a magnetron. Here's the picture from his patent on the microwave.
The first odd thing he noticed was that a chocolate bar in his pocket melted when he was standing next his magnetron. The next thing he tried was popcorn and that started popping too. The day he showed his discovery to someone else in the laboratory using an egg. As they watched the egg it exploded on their faces. It was like recreating the birth of the universe.

“Exploding an egg in a microwave is like the start of the Universe?”

Don’t you see? Lemaitre’s cosmic egg, explosions, egg on my face for not believing in it.


Well next time you cook popcorn you should think about the start of the universe but just don’t try the egg trick. Trust me it explodes and trust me you’ll get in trouble.


  1. bigbanger said...
    Ok, how is it that as we get more powerful telescopes, and we can see farther into space, like say 12 billion years back in time, what happens when we can see far enough back to see the big bang happen, how did we get out here before the light from that occurance. What's out past the farthest galaxies, and how far will everything keep expanding? Will it all come to a stop, and start to implode?
    Anonymous said...
    now i'm not totally sure of this theory but i'm pretty sure that someone stated possibly hawkings, i dunno, i'm not great in the memory department, but basically once the universe expands to a point, the gravitational pull that the universe will have aquired through the creation of planets, stars etc. will be so powerfull it will implode the universe.

    now if this is true which it may be, then what says that it hasn't already happened before, exactly like this but contracted to the starting point of the primeval atom or egg, and started once more, and if thats so could everything of happened pretty much the same way, i may of already typed this comment thousands of times before, this is simply a theory a 16 year old has created, possibly due to lack of sleep, but it could be true
    Anonymous said...
    Current observations suggest that rather than slowing down, the expansion of the universe is accelerating due to something called dark energy.
    Anonymous said...
    Actually, it is a cycle. Like the cycle a rubber band goes through except the universe is limitless so it keeps expanding and contracting. Actually, there is no such thing as time- it is an invention of our perceptions.

    But anyway, I did do the egg trick all over my mother's new microwave about ten years ago, and it was quite a mess, but I will never forget it.

    Also, I tried it again later. Had to make sure it was still going to explode. This time I took it out after a few seconds and avoided the explosion. I didn't care for the way it tasted, though. If you want a hard boiled egg in a hurry, turn the water up to high, salt and cover it; when it boils, boil the egg for one minute, turn off the water and go take a hot shower. Then come back and eat a perfectly cooked boiled egg. If it isn't cooked perfectly, put it in a rubber band and use it to conduct experiments on planetary impacts.
    Anonymous said...
    I'd like to know who lit the match!
    Also if it is true that for ever action there is an equal and opposite reaction then there shuold be a negative to our universe? Or a positive depends weather or not we're the negative or positive? I think!!! help please, another one of those things that have been bugging me for years.
    I'm typing this on my computer thinking that there is a negative or positive of myself typing the same thing?
    Anonymous said...
    I there is a negative of yourself, would'nt they be typing the opposite of you're typing?
    Anonymous said...
    The negative or positive of you would know the answer to your question and all your questions. But wouldn't know anything you know, and would know for every reaction there isn't an equal and opposite action and also would know why the universe is contracting.

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