Expanding universe

[Maniac]

I know nothing about science but had a bizarre thought the other day that I wanted to share with someone.

We know the universe is expanding and observe the doppler effect. Could we place cameras on several high constant speed spacecraft travelling at different speeds and pointed those spacecraft cameras towards the further point in the universe that gives off light. Those cameras would record different reds and if one records white light would that mean that the camera is travelling at the same speed of the further space object and could we use this data to calculate the age of the universe?

[MajorMitchell]

How many supply centres will Maniac need to get a (Hans) Solo win in a continually expanding Universe ?

[Jamiet99uk]

Maniac, we know the age of the universe. 6,000 years. Jesus said so.

[Mercy]

Those cameras would record different reds and if one records white light would that mean that the camera is travelling at the same speed of the further space object

Not everything in the Universe gives off white light. I think you mean to say 'light that is of the same color as it would expected to be if the light wasn't Doppler shifted' instead of 'white light'. The answer to your question then is: not exactly. See, the light from distant objects is Doppler shifted because of the expansion of space, while the spacecrafts experience another Doppler shift because they are moving through space, and these work a bit differently. Moreover, any further space object that the spacecrafts receive light from will have traveled significantly farther since the moment it emitted the light.

and could we use this data to calculate the age of the universe?

We indeed use Doppler shift to calculate the speed at which things are receding from us, which we in turn use to calculate the age of the Universe. Launching spacecrafts is quite a tedious way to measure Doppler shift, though. You can just measure the light while standing still, and then calculate the Doppler shift.

[damo666]

See?

[damo666]

Mercy: in proper English travelling has two ls and further is preferred to farther. B+

[Mercy]

See?

I meant to say 'You see'.

Mercy: in proper English travelling has two ls and further is preferred to farther. B+

Thanks, always nice to expand your knowledge of the English language.

[MajorMitchell]

Or did Mercy intend to refer to the Farther who art in Celestial Heaven as her far distant object ? In which case it's Father, not farther, or further.

[JECE]

Um, I don't see what the "further" adds to Mercy's sentence (I think it could be dropped), but the "farther" that appears later in the sentence is perfectly accurate in the English I know.

[Octavious]

I'm extremely disappointed that no-one has taken this opportunity to make fart jokes. But I guess fart is very close to Trump, and we then run the risk of being banished to the politics cupboard.

[Octavious]

I actually rather like the question, though. It's rather fun.

You have two immediate problems. One is that you'll need a damned impressive piece of kit to take measurements. The other is that redshift from the expansion of the universe can look pretty much identical to the redshift you get from stuff moving away in the traditional sense, and in the universe there's a lot of stuff moving damned fast. So in order to make sure you're focusing on cosmological expansion redshift you'll have to look at the further away stuff where expansion dominates over traditional velocities peculiar to that object. That means your space craft has to be going damned fast. Far faster than we can make anything go at the moment.

Of course, when we do have the technology to make things that fast we will have far more exciting things to do with it :).

[Maniac]

How fast do we think the universe is expanding?

Octavious makes a good point about is it redshift we're observing or is there something else making it appear like redshift?

I's suggest that if what we think is red shift is actually just red light, then that could be confirmed with my experiment. For example if we didn't know the ice-cream truck was playing Green Sleeves we would still be able to detect how fast it was going by sending out several cars following with microphones at different speeds. Only the car travelling the same speed will pick up the repetitive noise for some time.

[Maniac]

The answer to your question then is: not exactly. See, the light from distant objects is Doppler shifted because of the expansion of space, while the spacecrafts experience another Doppler shift because they are moving through space, and these work a bit differently.

Could you explain how it's different, I'd be interested in that if you could explain in simple language. TIA

[CptMike]

How fast do we think the universe is expanding?

The speed of the expansion of the universe is the "constant" of Hubble : it is around 70 km/s/Mpc ie something lower than 1 out of a billionth of % per year

[Maniac]

Octavious - if we experimented on a light source 1 megaparsec away it will be moving away at 'only' 70km/s - we have rockets that go close to that speed don't we? - If not could we begin by looking at a light source 1/2 megaparsec away?

[Octavious]

Rockets? I think the very fastest we've built go around 10km/s. Using gravitational tricks and a lot of patience we got a probe to around the 70 km/s mark. But that's using the earth as a reference frame. The earth itself is moving at 30km/s to the Sun. The average star is moving around 100 km/s to the galaxy. Some stars push 1000 km/s. That's a lot of noise. How do you know what you're looking at isn't just one of those things that happens to be moving away from you? How do you see your cosmological expansion through the noise of bog standard velocity?

[CptMike]

On the practical point of view, this expansion is only valid in empty space. It is influenced by gravity, so it is reduced around stars. That may have some influence for this experiment...

Anyway, interferometry is very precise and efficient. We don't need to reach the 70 km/s. We can go much slowier and just measure the little shift.

Some calculcations need to be done but I wonder if this could not be done with some spacecraft as Pioneer 11 but this has to be checked.

[Maniac]

Octavious - on the ground it would be easy for us (not me but people who know what they are doing to get a car to match the speed of an ice cream truck playing a tune the computer wizardry in the car didn't know. So long as the tune was on a loop and background noise was fairly constant. That's all we have to replicate with light in the near universe.

[Maniac]

Anyway, interferometry is very precise and efficient. We don't need to reach the 70 km/s. We can go much slowier and just measure the little shift.

Thx for introducing me to interferometry

[Octavious]

Octavious - on the ground it would be easy for us (not me but people who know what they are doing to get a car to match the speed of an ice cream truck playing a tune the computer wizardry in the car didn't know. So long as the tune was on a loop and background noise was fairly constant. That's all we have to replicate with light in the near universe.

What makes you think the noise will be constant? What you're trying to do is like listening for a siren that's slightly off in a city full of ambulances moving at varying speeds in varying directions.