Expanding people in an expanding universe?

[Canute]

But I thought the current theory is that space is expanding. Are you saying that isn't the case?

 

[Nereid]

Echoes - sharp probes of dust

Nereid wrote (re dark matter and dust): Perhaps it's just dust? If it were warm, it'd glow in the far-IR/microwave bands (if hot, in near-IR and optical); we don't see any. It'd also absorb light (IR, etc); we don't see such absorption.

There's another, independent, technique: echoes. When a really, really bright point source suddenly shows up (and then fades), it's like a strobe light through all of space between the source and us. From our point of view (POV, does anyone use this shorthand?), we will see 'circular' echoes of the flash, which are reflections of the flash off things just outside the line of sight between us and the flasher (hope that's not porn to PF ). Study of these echoes can identify all kinds of interesting things, and confirm our understand of the amount (and distribution) of dust.

Historically light has been where such echoes have been seen (e.g. from the supernova in the LMC). Recently X-ray echoes have been observed from a particularly bright GRB:
http://t2wesa.r3h.net/export/esaSC/SEMUFH474OD_sensations_0.html