Q2: isn't "speed of light in vacuum" misleading?

A positive displacement vacuum pump moves the same of gas with each cycle, so its pumping speed is constant unless it is overcome by backstreaming.

The speed of an electromagnetic wave in a vacuum can be derived from electrodynamic laws as:

In the 1800s, when pneumatic tubes shot telegrams and small items all around buildings and sometimes small cities, the future of mass transit seemed clear: we'd be firing people around through these sealed tubes at high speeds. And it turns out we've got the technology to do that today – mag-lev rail lines remove all rolling friction from the energy equation for a train, and accelerating them through a vacuum tunnel can eliminate wind resistance to the point where it's theoretically possible to reach blistering speeds over 4,000 mph (6,437 km/h) using a fraction of the energy an airliner uses – and recapturing a lot of that energy upon deceleration. Ultra-fast, high efficiency ground transport is technologically within reach – so why isn't anybody building it?

I know light's speed in vacuum is constant

Centrifugal evaporators were invented in 1960s by Savant Inc of USA, with their SpeedVac brand.[] Now it seems that physicists have come up with a new way of changing the speed of light in a vacuum. Over two years, and colleagues at the University of Glasgow, together with of Heriot-Watt University in Edinburgh, designed an experiment that can determine whether light with a certain "spatial structure" travels substantially slower than regular light in a vacuum. The researchers created a source that emitted pairs of photons simultaneously. One of the photons went straight to a highly precise photon counter, while the other went via two liquid-crystal masks, which imparted their profile onto the passing particle of light.

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Of course, light can appear to slow down if it travels through a dense medium – a result of the photons having to interact with the medium and take an indirect route through it. In water, the speed of light is roughly 225,000,000 m s–1, while in glass it is roughly 200,000,000 m s–1. The change can be even more drastic – particularly in highly "nonlinear" materials, in which light's speed can be reduced to just a few metres per second. Strange effects can also occur in a vacuum, including the Gouy phase shift, which happens when a beam of light is focused to a point and results in a tiny increase in its "phase velocity".

The speed-vac is used to concentrate small-volume samples