A fraction of a second after the Big Bang, the universe was white-hot chaos: New particles and their antiparticles were being created and destroyed constantly. As the universe expanded and cooled, new particles stopped popping into existence and many of the existing particles annihilated with their antiparticle or decayed into lighter, more stable particles.
If the very lightest particle was stable and neutral, it would have survived the chaos and would fill the universe to this day. That’s the idea behind the weakly interacting massive particle, or WIMP. The “weak” isn’t a dig — it specifically refers to the weak force, which is one of the four fundamental forces in the universe, alongside the strong force, the electromagnetic force, and gravity.
This particle would only interact with other particles via gravity and the weak force — not the electromagnetic force, which is why we wouldn’t be able to see it. If WIMPs exist, models suggest that they must be five times more plentiful than regular matter, which lines up with how much dark matter scientists think is out there. But every experiment we’ve run to detect this theoretical particle has failed, and by this point, most researchers have ruled it out.
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