quine's wiki | Main / LightEchoes

Information about the Big Bang, about the very origins of our universe, was thought lost to us forever. But a paper published just this year (2015) shows that we might be able to reconstruct this information. Read on to find out how.

We haven’t been able to prove that anything travels faster than light. All the information we have about distant galaxies, or even within our own galaxy, is from the light produced by them.

Light that we can see (visible light) has colours from red to violet. Each colour of light has a different frequency just as each note on a scale has a different frequency in sound waves. If you increase the frequency past violet you get Ultraviolet rays (which give you a tan and energy your body can use to make Vitamin D, or skin cancer depending on the frequency and length of time exposed). (https://en.wikipedia.org/wiki/Electromagnetic_spectrum) Past that are X-rays (used for medical and dental diagnostics), then gamma rays. Gamma rays are caused by radioactive substances and by pulsars (quickly rotating neutron stars) and quasars (supermassive black holes surrounded by and consuming lots of matter). In fact, pulsars and quasars emit light across the whole spectrum. But for this talk we’re more concerned with going the other way, past red into the Infrared (which we use for night vision goggles) and past that to microwaves and radio waves, the same microwaves that heat our food and the same radio waves that we use for cell phones, WiFi, and to communicate with our robots on Mars and out further into the solar system (like New Horizons, that just passed Pluto).

To really understand the origins of the universe, we have to look back in time. We can actually do that because the farther away things are, the longer the light has been travelling to get to us. If we look out at something that’s 10 billion light years away, the light was actually emitted 10 billion years ago. How do we know how far things are away?

If things are really close, say inside our house, the distance between our eyes give us two pictures that our brain can turn into a 3D model. We have an innate sense of how far things are away in our house. We can use the same idea using the Earth itself. We can take a picture with a telescope in spring, and then another in autumn when the Earth is on the opposite side of the sun in its orbit. Then we can figure out distances to stars that are close by. Further out, we have to use something else.

Imagine a party balloon on Earth, filled with air. The air inside has a pressure, as all gasses do. This pressure pushes outward on the inside of the balloon. The balloon material, stretched by the pressure of the gas, pulls back. If no air is leaking out, and the temperature of the air inside or outside doesn’t change, it stays the same shape and size. It has a teardrop shape because of gravity. On the International Space Station, it would be almost a sphere.

Now let’s talk about stars. A star is a ball of gas, just as a party balloon is full of gas. The pressure of the gas, coupled with the energy of fusion (and other processes), push out, while the gravity of all that gas pulls in, making a sphere. If the pressure pushing out isn’t enough to counteract the gravity, the star collapses inward, then some of the heavier elements start to fuse, creating more energy that then counteracts the gravity and the star explodes.

There are various specific situations when stars explode (go nova or supernova). A type Ia (roman numeral 1, a) supernova happens when a white dwarf and another star are close together and the white dwarf is slowly pulling matter from the other star into itself. Because the process is slow, the star always goes supernova with exactly the same mass every time it happens throughout the universe. Just as a candle is bright when it’s right next to your eyes and that same candle is barely visible if someone takes it down the road, we can use the brightness of a type Ia supernova in distant galaxies to find out how far away it is. In fact that’s just what we call it: a standard candle. There’s another kind of standard candle we can calculate from pulsars that give us distances in our own galaxy.

Now we’re going to go on a tour out to the farthest reaches of what we know exists. To do that, we’re going to need two superpowers. The first one is that we’re going to have to be able to tell how far away things are. We’ll leave the other one for now. This superpower lets us experience directly what we know about the universe from various telescopes we’ve built on Earth and in space. So even though we’re pretending, the things we’ll see are real and we really know how far away they are.

If we go up to Algonquin Park on a dark night, far away from any city lights, depending on the exact date and time, we might see the moon and we’ll no doubt see some of the planets. Past that we are pretty sure there are trillions of comets, much too small to see, but still in orbit around our Sun. (https://en.wikipedia.org/wiki/Oort_cloud)

Then there are the stars close by in our own Milky Way galaxy. Some of the brightest are Rigel, Vega, Arcturus, and Sirius (the brightest star that can be seen from the northern hemisphere). All these can be seen with the naked eye. The centre of the Milky Way galaxy is low in the southern sky, and the band of the Milky Way sweeps upwards in an arch like a river of stars across the eastern sky back down to the northern horizon. If you haven't seen it, you should. It's beautiful.

Past our own galaxy is the Andromeda Galaxy, the nearest major galaxy to the Milky Way. It’s a spiral galaxy like our own. It’s just barely visible to the naked eye as a not very bright smudge. Andromeda contains one trillion stars: at least twice the number of stars in the Milky Way, which is estimated to be 200–400 billion. Past that are other galaxies, far too many to even think about counting without computers.

Now we’re going to need that other superpower. We’re going to have to be able to see microwaves. Because beyond all the innumerable galaxies is a perfect sphere of microwaves called the Cosmic Microwave Background (CMB), preventing us from seeing beyond it like a brick wall. The frequency coming from every direction is almost exactly the same, but there is a tiny variation in the frequency. The CMB is from a process called recombination that happened roughly 378,000 years after the Big Bang. “Looking” at the CMB is like being at the centre of a (spherical) egg and looking at the inside surface. Every photon from the CMB has been travelling for nearly 14 billion years to get to us, but the inside surface of the egg would appear to be 46 billion light years away. The difference between 14 billion years and 46 billion light years is because space itself has actually been expanding all the time from the Big Bang on.

(To see a full picture of how far away everything is from the centre of the Earth out, see http://www.astro.princeton.edu/universe/all200.gif.)

Since we can’t see beyond the CMB, we can’t look any further back into the past. Anything we think we know about the universe before recombination we can’t observe directly and is all theoretical.

Now we get to the paper that was released this year(1). Any light that was directly from the Big Bang has already passed us by. Just as if a hypothetical alien civilization tried to send a single message directed at Earth 1000 years ago but we hadn’t made radio telescopes yet, we missed the message and it’s gone forever...or is it? Enter quantum mechanics.

Things that are really small like atoms and photons(2) have some very weird behaviour that violates common sense. Theories about how electrons moved in atoms were imagined to be much the same as how planets orbit the sun in our solar system. The idea that atoms (the very small) might work essentially the same as planets (the very big) was popular through time and culminated in the Bohr model of the atom around 1911. However, experiments done show that the very small and the very big have many differences.

Things can appear to work differently based on how you observe them: light can act like a particle or a wave. Heisenberg’s uncertainty principle shows that attempting to measure one attribute such as velocity or position may cause another attribute to become less measurable. Simply observing something at all can cause it to change (Schrödinger's Cat). Empty space (vacuum) can be shown to contain “virtual particles” that appear to pop in and out of existence creating a “quantum foam”, and as space is constantly expanding, this energy is also increasing over time, yet with no visible counterpart. Things can even appear to be in two places at once (quantum locality and the double-slit experiment). All these things have no counterpart in the kinds of objects we deal with in everyday life.

The paper shows that using quantum mechanics, we can find a kind of “echo” from our hypothetical alien civilization that tried to send a single message directed at Earth 1000 years ago, or indeed from any light, such as from the Big Bang itself. No information can travel faster than light, but there is something “left over” after it passes. This information fades with time, but slowly enough that with enough quantum detectors that are “entangled” (they have a special property that is shared between them) we can compensate for that loss, and reconstruct information about the Big Bang that we thought we had lost forever. In order to cut down on noise and get a clearer signal, we would need to take these detectors into space (to avoid noise caused by gravity) and we would need to cool them down as much as possible. We can create small numbers of entangled photons, we can take things to space and we can cool things down to just about as cold as things can get, but we can’t yet do all of these things at once. It’s not too far fetched to believe that in the next hundred years it will be possible.

Also, we believe that information can't be destroyed (as per Leonard Susskind (YouTube)) even by black holes. We thought the information might come out in Hawking radiation, but the general consensus so far is that there isn't enough information coming out to balance what the black hole swallows. The idea that information from light can be reconstructed after it passes may provide an answer to this problem.

(1) For the details of the paper and more about it, see http://backreaction.blogspot.ca/2015/05/information-transfer-without-energy.html?m=1.

(2) One photon is the smallest possible amount of a particular kind of light (visible, infrared, x-ray, etc.) in much the same way that an atom is the smallest amount of a particular element (gold, titanium, copper, etc.).