Can we ever be able to travel with speed of light?

From more than a century humankind is asking about could we ever be able to travel with speed of light, Is travel with speed of light is possible?. As space enthusiasts, could space ships shown in movies star trek and star wars be possible, can we make warp drives?

Let us first discuss about speed of light. It is a cosmic speed limit. Speed of light is fastest speed of which any two poles in space can communicate with each other. It is a speed at which light travels. In one second a beam of light can make 8 rotations. The standard speed of light if we convert to km/hr than speed of light is 1,079,252,848.8 km/hr(1.07 billion km/hr). Or we can say 299,792,458 meter/sec. So again question arises can this speed be achievable. If we can make to travel with speed of light then to reach to our nearest star Proxima Centauri it will take 4.2 earth years. So if we travel 5 times speed of light then to reach proxima centauri it will take nearly 1 year.

In 1994 a Mexican physicist Miguel Alcubierre published a theory, in which he showed how a warp drive is possible with Albert Einstein’s Theory of General Relativity. He said that in order to make a warp drive it will require a huge amount of negative energy. Negative energy equivalent t mass of Jupiter.

Alcubierre said that if the lift hand side of Einstein’s equation is for curvature of space-time, right hand side is newton’s gravitational constant with T is stress energy factor, then there requires a negative energy in right side to bend fabric of space-time. Alcubierre determined that the ship needed to stay inside a flat space-time bubble, which is such that it can move with any arbitrary speed.

But, Alcubierre’s theory is as real as fiction. As we know that negative energy is not possible and does not exists. Anti matter exists and is different from negative energy. Anti matter is a regular matter with opposite charge but with it has positive mass.

In 2021 paper by physicist Erik Lentz of Gottingen University showed that space time warp bubble solution is possible by positive energies and theoretically move at any arbitrary speed.

Again we have question that is warp drives be possible? The answer is Yes.

In recent papers published by Advanced propulsion laboratory at Applied Physics authors Alexey Bobrick and Gianni Martire showed that how warp drives are possible without negative energy. They showed that we can travel with some fraction of speed of light, but to travel faster than speed of light you would need a superluminal matter. In other words, you would need a matter that travels faster than speed of light. Accelerating anything with mass to speed of light requires an infinite amount of energy. This would be true for any warp engine design, but is impossible.

Gianni and Bobrick showed that there are four types of warp drives, of which Alcubierre showed class 3 type. They showed that Class 1 type of warp drive is physically possible with positive energy and real matter and they don’t travel with speed of light. These classification is based on speed inside the bubble(Vin) and speed outside the bubble(Vout).

These can be achieved by time dilation. Gianni and Bobrick proposed two ways of time dilation, either you go really fast with 90% of speed of light or you put yourself into a strong gravitational field. The stronger the gravitational speed the slower the time passes for passengers. If we make a ship of super dense material, perhaps close to mass of a neutron star then gravitational field will be strong enough for time dilation. They designed a shape, if the ship has diameter of 620 meter with mass of 10% as of sun then time for the passengers inside the ship will be 1/10. The passengers will travel to Proxima Centauri in 9 Earth years but for passengers inside ship will feel as of 10 months.

But to move such a massive ship we need a powerful engine. If we convert its 13% mass to energy than we can get enough energy. The one way is fusion as it converts 1% of mass to energy. The one Bobrick and Gianni proposed that if we take advantage of Gravitational Accretion Energy. This is disklike flow of dust, gas and plasma orbiting around a massive astronomical object. The friction and loss of angular momentum creates huge amount of energy that potentially be harnessed. Accretion disk can convert 10% of any given mass into energy which is highly sufficient.

Now the question is no longer “If” humanity will achieve warp travel, now the question is “When”.

Credit: Arvin Ash: Reference Papers: Bobrick and Martire: Website: Lentz: