Phenomenal cosmic power, itty bitty living space

Wouldn’t it be great to take the universe in the lab? Astronomy is one of the most captivating parts of physics. I mean, one can’t scoff at the idea of unveiling the mysteries of the cosmos. Unfortuntely, galaxies and black holes don’t exactly cooperate as far as experimenting goes.

A group of physicists is working on a solution. Continue reading


Wormholes: digging tunnels through space

Sometimes science fiction tells us stories of technology we can almost grasp already, like traveling to Mars. Other times it’s much more far-fetched and outrageous stuff, like wormholes. Since general relativity doesn’t explicitly, entirely forbid them, they have fascinated scientists and authors alike.

An example of a wormhole connecting regions of two-dimensional space. credit:

A wormhole is a tunnel, a shortcut between two far-apart regions in spacetime. The movie Interstellar had many flaws, but at least plausible science (thanks to the supervision of star physicist Kip Thorne). They also explain quite effectively the idea of wormholes: take a sheet of paper and fold it in half, then punch a hole through it. You just created a wormhole in your paper universe.

The entrance should look like a black hole, an inescapable sink where light and matter disappear forever. The exist should be the opposite: a source from which matter and light spring eternal—a white hole. Through a wormhole, you’d be able to cross immense distances in relatively short times. But, probably, not travel in time*.

So do they exist?

For sure we can’t make them. Making wormholes with paper is cute, but it only works because the sheet is two-dimensional and we are comfortable handling three. To create a real wormhole we’d need to work in four dimensions which is a non-starter for now.

It’s also unlikely that naturally-occurring, large wormholes exist. First, at least observing a white hole would give some indication of the existence of wormholes, but we’ve never seen them. Secondly, keeping a macroscopic wormhole open requires something that turns gravity from a force that pulls things together to one that pushes them apart. And we’ve never seen that either.

Still, I find really cool that we can imagine such an outlandish thing and actually reason about them, make sound arguments on how it could or could not work.

A simulation of what a wormhole from the university Tübingen (Germany) to the dunes of Boulogne (France) would look like. CC-BY-SA CorvinZahn/Gallery of Space Time Travel, via commons

If you want more
  • There’s plenty of semi-accurate explanations around about wormholes. But I liked this more serious one on Chalkdust
  • NASA does a great job seriously answering all sorts of wormhole questions on this page
  • Some say black holes are actually entrances of wormholes to other universes. Maybe, maybe not. Black holes are freakin’ weird.

* MINOR SPOILER: In Interstellar, Cooper does sort of travel in time, too. But that only happens after stepping into other dimensions: we’ve already crossed into magic.

Cover photo: CC0 Pexels/pixabay

All physics is wrong!

Quantum Mechanics: wrong! General Relativity: wrong! The standard model of particle physics: wrong, wrong, wrong.

All physics (actually, science in general) is wrong—to some extent. And scientists know about it, too! Here’s the thing: science has to be wrong. Because it doesn’t find The Truth, instead it explains what we see around us as well as possible.

Even when we have an explanation for what we see, there might be a better one we missed.

Newton thought gravity was a force between objects with mass. That’s pretty much right. Enough to get you to the Moon at least. He never thought of mass warping spacetime. But he also never saw gravity bending light (which has no mass), or affect the passing of time. Einstein, with his General Relativity explained everything, including these things, which he never even observed!

You can describe the motion of all planets, perfectly, keeping Earth at the center. It’s just very complicated and more wrong than Newton’s gravity. credit: wikimedia

Indeed, a good theory must predict new stuff, stuff we haven’t seen. Before Newton, people described the motion of stars and planets as circles moving around circles, around circles. Whenever something didn’t fit, they’d add a circle. It perfectly described, everything we could see, but couldn’t predict anything new. Newton’s laws told astronomers where to find a new planet: Neptune.

Whenever a prediction turns out wrong, scientists find out a new way to explain the new facts, then move to new prediction, and the cycle restarts.

Soner or later, something will come along and prove General Relativity wrong. Personally, I think dark matter (an invisible, untouchable substance that just has to be there) will be the next battleground. Challengers are stepping up.

What our universe is made of (according to current theories): 95% is “dark” stuff (a fancy way to say we have no clue what it is).

Just like Relativity, all other theories will eventually fall. No theory is perfect, but each newly-accepted one is better than the last. At any time in history (well, at least since we’ve had the scientific method at least), scientific facts were the best explanations of the world. Ever. And that’s still true now.

It’s good to keep an open mind, but also to keep in mind why facts are considered facts. If you open your mind too much, you risk your brain falling out.

If you want more
  • You can literally write books on all the stuff we don’t know. Jorge Cham did.
  • A detailed explanation of what works and what doesn’t around dark matter on PBS Spacetime:


Cover photo: Facepalm, CC-BY Brandon Grasley/flickr

The relativity experiment you hold every day

After the discovery of gravitational waves, there’s a lot of talk about Einstein’s General Relativity. We usually talk about it in the context of black holes and other things we don’t quite see every day, but I bet you held a relativity experiment in your hand in the past 10 minutes. Indeed, if you used a smartphone or anything with a GPS, you effectively performed a general relativity experiment.


Indeed, the 31 GPS satellites actually spend their days broadcasting the time on the super-accurate atomic clock each has on board.

The signal takes a few hundredths of a second to reach you on the ground. So comparing very accurately the time on your watch to the signal from the satellite, you can calculate how far it is. Putting together the distance from enough satellites, you will find your own position on the planet.

Only one point on the surface of the Earth can be simultaneously at certain distances from four GPS satellites. That’s where you are. Credit:

It’s all nice and fine up to here, but what does this have to do with relativity?

According to the theory, higher up in gravitational fields (say, when you’re orbiting in space) time flows ever-so-slightly faster. A minute in orbit is a teensy weensy shorter than a minute on Earth. As usual with relativity, the effect is small, so small you wouldn’t notice.

Because the effect is so tiny, GPS satellites were first deployed with relativistic corrections turned off. Scientist figured it wouldn’t make a difference. Boy were they wrong: in a short time, the localization was off by kilometers.

Since they also thought this might happen, the scientists had made possible to switch on the corrections from the ground.

So every time your satnav tells you where to turn, every time Google Maps tells you accurately how far the nearest pub is, you’re actually confirming that General Relativity is correct.



Coverpote photo: CC0 Sylwia Bartyzel, via unplash

Four fundamental things about gravitational waves

The team at LIGO (the Laser Interferometry Gravitational-wave Observatory) annouced they directly measured the gravitational waves emitted by two black holes merging into one. What are they talking about? Here’s the answer to 4 of the most common questions (plus 2 extra-credit, if you feel up to it).

The merging of the two black holes, and the resulting gravitational wave. NASA

What are gravitational waves?

Gravitational waves are ripples in space-time predicted by Einstein’s General Relativity theory. If you heard anything about this theory, it probably is that, by their mass, objects warp space-time around them.

If mass is moving in the right way, it should (in theory) create gravitational waves. These propagate in space like ripples on a pond. They periodically make it longer and narrower, then shorter and broader, and so on.

Credit: MOBle/English Wikipedia

Credit: MOBle/English Wikipedia

Edit: Confused by the “stretching space” thing? I unpacked this (using puppies!) in a later post.

How big is the effect?

Tiny. Less than tiny: unfathomable catastrophes (crashes between black holes, supernovae exploding, stuff like that), relatively close (which means within our galaxy) change the distance between Earth and the Moon by about a thousandth the width of an atom.

As you can figure, an effect this tiny is pretty hard to measure.

How did we find them?

LIGO is a laser interferometer. It works by splitting a laser beam in two: one goes on its original way, the other bends 90 degrees away. Each of them bounces back and forth a few times a few hundred times along a tube. Then the two laser lights meet again, so that their lightwaves interfere with each other, perfectly canceling each other.

If a gravitational wave is to pass through the device, it stretches and shortens each leg, alternatively. This breaks the perfect synchronism between the two laser waves. The scientists looked for this sort of signal, where the two laser branches were out of sync.

To be absolutely sure they eliminated every disturbance, then, they looked for identical traces to appear in both a detector in Northwestern US and one in the Southeast. An additional detector, the Italian VIRGO, will join soon.

If the effect is so tiny, why bother?

Because gravitational waves provide a completely new way to perceive and study the universe. As Catherine Man, of the French Observatoire de la Côte d’Azur, said

Now we are no longer observing the universe with telescopes using ultraviolet light or visible light but we are listening to the noises produced by the effects of the gravitation of celestial bodies on the fabric of space-time

Among the things we could “listen” to there’s the echo of our universe’s youth. Until it became 380 thousand years old, the universe was opaque: it didn’t let light through. So we couldn’t observe anything earlier than that time using electromagnetic waves. But gravitational waves already existed, if we could hear them, we could learn much.

Extra credit for confident readers

Didn’t someone find gravitational waves a few years ago?

Yes and no: gravitational waves carry energy, and in 1993 Russel Hulse and Joseph Taylor did indeed win a Nobel prize in physics for observing that very energy. But, until now, nobody measured gravitational waves directly.

Also, last year, the BICEP2 project announced they found them. They were wrong. They didn’t look good that time.

So what changes with eLISA now?

Likely, not much. eLISA is a space observatory for gravitational waves planned by the European Space Agency, slated to launch in 2024. Even if gravitational waves won’t be new by then, eLISA is much much more sensitive than LIGO.

Basically, it will be a larger ear, capable of measuring different, fainter, farther away sources. And, being in space, it will experience much less disturbance.

If you want more
  • For the first anniversary of the discovery, we dug deeper: what does it mean to stretch space? how do you measure the stretch at all? And explained it with puppies!!

Cover photo: CC0 Austin Schmid, via unsplash.