Travelling at the speed of light is not just hard but impossible for anything that has mass, since it would take infinite energy, so the real question is how close we could get and whether the loopholes physicists talk about are more than mathematics

Every space story worth its salt eventually reaches for lightspeed, the moment the engines catch and the stars streak. It is one of the oldest dreams in science fiction, so it is worth saying plainly what the physics actually allows, and what it flatly does not.

The blunt answer is that travelling at the speed of light is not merely difficult for anything with mass. It is impossible, and not in a way that a better engine will one day fix.

I am a writer with a long interest in this material, not a physicist, so treat this as a careful reading of settled science and clearly labelled speculation, kept apart.

Why light speed is a wall, not a target

The problem is built into relativity. The faster you push an object, the more energy each additional increment of speed demands, and the returns shrink as you approach the speed of light. To actually reach it, the energy required rises without limit. You would need an infinite amount, which is another way of saying it cannot be done.

Light itself gets to travel at light speed for one reason: photons have no mass. Massless things must move at that speed, and things with mass never can. The speed of light is not a speed limit that a clever enough spacecraft might one day break. It is closer to a feature of the shape of spacetime, the same for everyone, everywhere.

So the honest reply to “will we ever travel at the speed of light” is no, not us and not our machines, because we are made of mass.

How close could we get

The more interesting question is how near that wall you can press, and here the news is better, at least in principle.

There is no limit stopping you from approaching light speed, only from reaching it, and relativity throws in a strange gift on the way. As you travel faster, your own clock runs slow relative to the people you left behind. A crew moving close to light speed could in theory cross many light-years while ageing only a little, even as decades or centuries passed back on Earth. The distance does not shrink, but the time you personally spend crossing it can.

The gap between that principle and anything we can build is enormous. The fastest object we have ever launched, NASA’s Parker Solar Probe, travels at less than a tenth of one per cent of light speed. Even nature rarely gets close: a star whipped around the black hole at our galaxy’s centre reaches only about 3 per cent of light speed at its fastest, and that is one of the quickest large objects we know of.

The closest thing to a real plan

One concept comes nearer than the rest. Breakthrough Starshot, an initiative announced in 2016, proposes to skip heavy engines entirely and instead push a fleet of gram-scale probes with a ground-based laser, accelerating tiny light sails to around 20 per cent of the speed of light. At that pace a probe could reach the nearest star system, Alpha Centauri, in roughly twenty years rather than tens of thousands.

It is important to be clear about its status. This is a design and a research programme, not a spacecraft. The engineering problems, from a laser array of unprecedented power to a sail that will not vaporise, are unsolved. But it is the nearest thing to genuine near-light-speed travel that anyone has seriously put on paper.

The loopholes, and what they cost

If you cannot go faster than light through space, general relativity leaves a stranger door ajar: rearranging space itself.

In 1994 the physicist Miguel Alcubierre found a solution to Einstein’s equations describing a warp drive, a bubble that contracts spacetime in front of a ship and expands it behind, so the ship sits still while space does the moving. Wormholes, tunnels between distant points, are also valid solutions on paper. Neither would break the local speed limit, which is what makes them so tempting.

The catch is the same for both, and it is severe. They require what physicists call exotic matter, a form of negative energy that we have never observed and do not know how to make. Early estimates for a warp bubble needed more negative energy than the mass-energy of the entire observable universe. Later work trimmed that figure dramatically, but it remains vast, and the fundamental obstacle stands.

Recent designs have taken the opposite tack, dropping the exotic matter to stay within known physics, but the versions that need no negative energy are subluminal. They stay below light speed. As things stand, the maths permits shortcuts that the physics of building them cannot yet reach.

Where that leaves the dream

Put together, the picture is honest rather than romantic. At the speed of light, no, not for anything with mass. Close to it, physics allows what our engineering cannot presently manage, though concepts like Starshot show what trying would look like. Faster than it, only inside equations that call for a substance nobody has ever found.

None of this is likely to change at the level of the physics. What is worth watching is the near-lightspeed end, where a laser-driven sail or some successor might one day turn a fraction of the speed of light from a diagram into a departure.