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## Main Question or Discussion Point

Hi.

I read some basic cosmology where it is always said that density fluctuations, pertubations can be described in modes of waves. In particular if you use linearised theory where δ(x,t) is Fourier transformed δ(k,t).

What exactly is the reason for this? What do the wave modes describe?

Thanks

I read some basic cosmology where it is always said that density fluctuations, pertubations can be described in modes of waves. In particular if you use linearised theory where δ(x,t) is Fourier transformed δ(k,t).

What exactly is the reason for this? What do the wave modes describe?

Thanks