In the game Portal, there are glowing light platforms. These platforms are (supposedly) made of solid, compressed light. How can these realistically be made?
They are not realistic, not in the slightest.
In the real universe, there are two fundamentally different kinds of particles. Fermions are “matter-like” and ultimately that’s why bricks are solid and hard. The way matter behaves comes from the fundamental properties of these particles, which, e.g. cannot be have more than one instance in the same place.
Bosons are the opposite. They don’t take up space and prefer to pile together like a football tackle heap. That’s why lasers are a thing. Light uses bosons. Meanwhile, photons have no charge, so they don’t attract or repel each other in any way. The lack of charge is also crucial for light being what it is. For example gluons do have a charge (the ‘color’ charge of the strong force) and rather than spreading out in all directions so the intensity falls off with the square of the distance, they interact with each other and form flux tubes that act like rubber bands.
So the statement in the Question is an oxymoron. Light doesn’t do that. Something that did that would not be light.
Different Universe with something like that?
Now, in another universe with slightly different things in it but generally the same kinds of rules, the “flux tubes” sounds interesting. The nature of the charge and the particular energies involved make the strong force very short range and prevent the color charge from ever showing. But that’s details of the specific values involved, not because the bosons have charges per-se.
But a boson can’t just have any kind of charge. Bosons and charges work together and form a symmetry group. Light is intimately tied with the existence of the electric charge, but doesn’t carry the charge. That will be the case for a charge that has one “kind” like electric, with positive and negative values along a line of possible charge value.
Now you could have platforms made from electromagnetic forces forming loops and such, but that’s not how you described it.
or exotic forms of matter in general
And if you did have a “solid” of something that wasn’t made of atoms, why would it be solid against atoms rather than only the same kind of stuff? Recall that bricks are not solid because the electric charges repel each other, but because electrons are fermions and “exclude” each other.
As others have said, a solid platform made of light is completely unrealistic. However, it is entirely possible for light to exert a force on an object and hold it up, though the force required to support a human's mass against Earth's gravity would require a truly ferocious amount of light.
Using some serious estimation, a 1km square reflective sail in orbit around the Sun at Earth's orbital radius would experience a maximum of about 8 newtons of force from the sunlight hitting it. Cutting that down to an average foot size, about 0.03 square meters, you're looking at about 0.5 micronewtons of force across both feet. The force required to support an adult woman of Chell's approximate mass is 600-700N. So if her shoes were highly reflective, the platform would have to shine over one billion times brighter than the Sun in order to support her weight. That translates to well over a trillion watts per square meter. I could be way off on this, but if my math is right, that corresponds to the radiation emitted by something that is 160,000°C (290,000°F), assuming all of the light is emitted under her shoes at the time her feet apply pressure.
If you're writing a story, this could make for a really interesting failure mode...
Portal 2 is a comedy and probably the writers just stringed some scientific jargon together to construct an intentionally nonsensical scientific concept. Probably the writers put a lot less thought into this than we are right now...
Light is a massless particle that travels in a straight line. (incidentally it travels at the speed of light because it has no mass to slow it down.) Its path can be bent by gravity because gravity is not a force, but rather a symptom of the bending of space-time by mass. Because light is massless it cannot be held together by its own mass.
Light is also "charge-less" and therefore cannot be bent by electromagnetism to any measurable degree, as explained here
So compressed light would fly off and not hold together into a solid object. I also do not see what conceivable external device could hold it together, other than with strong gravity that would destroy the room. Also, it contains a lot of energy and would incinerate anything that touched it.
The other answers are correct in that solid light is not possible, however keep in mind that something similar to that and called that might be possible.
For example what if there were particles in the air that normally just act as a gas. When hit by a laser they clump together and form a solid platform. By shining a grid of lasers to form a hologram in the right location you get a platform made by light even though it's not made of light.
Those platforms would need to be supported somehow and there would be a lot of handwavium involved in the material they are made from but something along those lines is not inconceivable.
Some of the key traits of solid matter that make it solid matter are these:
- It tends to stay where it is.
- It excludes other matter from being in the same space.
- It has a shape and tends to hold onto that shape even in the face of attempts to change it.
In more detail, matter never moves at the speed of light in any frame of reference and there is always a frame of reference where it is not moving.
Light on the other hand is always moving at the speed of light. It will not stay where you put it and instead move away at the speed of light. The best you can do is change the direction it's going, and that ultimately requires something not moving at the speed of light to bend the light with (like an optical fibre or a black hole)
Matter is also made up of charge particles, arranged into atoms with positively charged protons at the centre, and negatively charged electrons around the outside. As atoms get close together, the electron shells on the outside will come together long before the protons in the nucleus get as close to the electrons. This means that when atoms are very close to one another, the repulsion between their electrons dominates over the attraction between the nuclei and their neighbours electrons.
This close range repulsion is called the Van Der Waals force, and it prevents atoms from overlapping. This is what makes normal matter (as opposed to say the matter making up neutron stars) take up space and exclude other matter.
Light has no charge, and two or more photons can be in exactly the same place at the same time (which is part of how lasers work)
What makes matter solid is that it can form structures which requires both the 'not moving at light speed all the time in all reference frames' and the charge differential between the inside and outside of atoms. Atoms near each other can connect into a structure that resists having those atoms moved apart. (This is a huge simplification)
Light is always moving at light speed, has no charge, doesn't exclude other light or matter from occupying the same space, and doesn't form structures with other light where the photons will resist moving apart from each other.
You can push things with light, but the amount of pressure you can get is small. By the time you have enough light to be noticeable in situations on typical human scales, the heat would be immense. Rather than a pleasantly glowing platform you could stand on, you'd have something more like an enormous laser shooting up into the sky and vaporizing everything in its path.