A stochasticly updated blog about interesting topics in Physics & Astronomy
A few years ago, researchers in CERN announced that they had found a particle which travels faster than light. For the next few months, physicists separated into 2 camps. Camp A said that the results were wrong, and the experiment had been done wrong, as nothing can travel faster than light. Camp B said “Ok, maybe the results are wrong, but what if they aren’t? What if there’s new physics here?” In the end, it turned out the clocks used for the experiment hadn’t been set right (or something similar to this), and the speed of light remained this maximum speed of anything ever. But why is that, and what consequences does it have for us now, and what would happen if we ever traveled faster than it?
The speed of light is 299,792 km/s, or more formally written as just c. So what does it mean to travel at this speed? Firstly, light is not a continuous beam of energy, as most people believe. Light travels as tiny amounts of energy, called photons, and these photons, which aren’t made up of mass, travel at a speed of c.
So what happens when an object with mass starts moving close to the speed of light? Intuitively, you would say that if an object is accelerating with nothing to stop it, its speed will keep on getting larger and larger, and it will go faster than light. Sadly, physics doesn’t obey intuitiveness when you’re dealing with speeds close to c. When an object gets close to c, and it “accelerates”, rather than getting more velocity, it gets more massive!
Energy and mass are equivalent. By saying that the average human is 72kg, what we’re actually saying is if that person’s mass were converted into energy, it would be the same as (by using Einstein’s most famous equation ). Another relation I’m going to use here is the idea of Kinetic Energy (or K.E. ). K.E. is the energy an object has because it has a velocity. Below is a graph showing how the 2 are related.
So, from the above, we can conclude one thing – the energy of a body can increase in 2 ways. Firstly, either its velocity can increase, or its mass can increase. For everyday objects, like cars and airplanes, the velocity is the quantity that increases. But when an object starts travelling close to c, things change, and the energy is added to the system by the mass of the object increasing. Which spells bad news if you’re trying to lose weight and decide to take a trip to your nearest star by traveling close to c.
Now for some other funky effects of travelling close to the speed of light. Most of us know time as being pretty constant – a second for me is the same as a second for you. But close to c, this no longer applies, and time becomes completely relative. The faster someone travels, the slower time passes for them. This leads us onto the twin paradox. Take 2 twins. Leave one on Earth (say Bob) and put the other (say Tim) in a spaceship to orbit the Earth for a while at a speed close to c. When Tim finally comes home, he’ll find Bob to be a lot older than he is, and this is because time passed slower for Tim while he was in the spaceship – kind of weird, right?
So, can things actually go faster than the speed of light? Well, we know that something that has mass most certainly can’t – if it gets close to the speed of light, the object will get more massive rather than actually get faster. This is seen everyday in CERN at the Large Hadron Collider. A proton moving very slowly has a mass of about . However, at CERN, protons travel very close to c, and their mass increases to . That’s an increase in mass of about 7,460! And the more energy is given to these protons, the more massive they’ll get. Now, we also know that photons travel at exactly c, and they can do this because they have no mass – they are pure energy. So, logically, something that travels faster than c would have negative mass right? Wait….what? What the hell does negative mass mean?
The concept of “negative mass” is best explained through use of light cone diagram. Below is a graph where the x axis represents a position in space. The y axis represents time (with the positive y being the future and the negative y being the past). The crossing of the x and y axis represents where you stand right now. The cones which are coming out represent the position in space you would go to if you were travelling at c. Hence, you can travel anywhere within your future light cone, and the past light cone represents every possible way which you could have used to arrive where you are. If you were a photon of light, you would follow the cone.
Everything outside of the light cone represents something that could travel faster than light – a particle of negative mass. This region is called Elsewhere. Theoretically, these particles exist, and have the strange power of being able to travel backwards in time (like the famed Tachyons from Star Trek). So, hypothetically, you can travel faster than light – you just need to have negative mass to do it.