system
Given the following post, respond as if you're commenting on Reddit:
human
[Portal] How sharp are the edges of portals?

Say you step directly between a portal and another, How sharp is the edge between them?
gpt
They're surrounded by a small gravity field that keeps you from cutting yourself on them and also generates the pretty orange and blue colours. When the portal closes on something, the field changes shape to move that object and prevent it being chopped in half. Some versions of the gun extend the field a few meters straight out from the portal mouth (in a very diffuse form, obviously) to make it easier for falling objects to pass through the portal without hitting the edges.

It's based on the same tech as the tractor beams and floating platforms Aperture was experimenting with. If you put your hand on one, you'll feel a mild repulsion, like a magnet pushing you away. Try to force past that, and the more intense repulsion will feel rather like an invisible frictionless surface about a centimeter above the portal's edge. You can't actually touch the portal's edge without modifying the portal gun, which is a good thing, since it's really damn sharp.

The reasoning behind them is that when you're testing the response of test subjects to deadly lasers, you don't want them getting sliced in half by anything other than the deadly lasers. Unless that's also part of the test.