Dear Sharon,
As-salamu alaykum
Verses such as these must exercise some interpretative and logical constraints. Whereas there is no doubt that God has made much of what is in the observable and natural realm subservient to mankind with His will, this is arguably not an
absolute reference to worlds we may have absolutely no control over and we are not allowed to penetrate. For example, arguably, a grain of sand billions of light years in a distant part of the galaxy is not going to be much use to man on Earth! The same could be argued for distant civilisations or other creations of God in the distant regions of the Universe who may have their own laws and reasons for existence in God's wider plan.
It is also noteworthy that the phrase
'heavens and the earth' can also be a reference to the observable sky and the lower heavens
[1], [2]. For example, in verse 55:33 there is a clear indication that the
'heavens and earth' can be
surpassed which is possibly then a reference to the lower heavens whereby these can be surpassed into outer cosmic space / deeper parts of the universe. Therefore, the term can indicate the immediate observable sky
and the outer heavens (further afield). There is clear recognition that God has granted man some
'authority / power' (sultan) to explore and conquer. But the phrase
'la tanfudhuna illa bisultanin' (Ye will never penetrate them save with (Our) sanction) also appears to present some limitations / control. The verse is also addressed to both man and jinn.
Therefore, the phrase
'heavens and the earth' may just be a reference to what is on earth and the immediate sky (not necessarily the outer heavens).
The verse that you have quoted (31:20) is then arguably a reference to the all things (which God has permitted and are of use to mankind from the Heavens and the Earth) and have been specifically subjected to the use of humans by His will. Of course, there are observable bounties and there are those bounties / forces that are obscured to our mind and are useful to mankind beyond the realms of our immediate knowledge.
However, the implication of
'all things' should not necessarily be interpreted in the
'absolute sense' but rather, in the remit of all what God has bestowed on us
for our use. For example, even though we may never be able to penetrate distant galaxies and stars, on Earth these objects in the night and their location in the sky can still assist in the navigation of travellers at sea and on land. However, there are galaxies and stars we may never see from the Earth which begs the question, of what use are they then to man?
Therefore, given the above, this does not mean that every alien, jinn and or angel is automatically created as slaves (as you have put it) / subjugated for mankind's use. The verse must arguably have a logical constraint within its interpretation.
I hope this helps, God willing.
Joseph
REFERENCES:[1] HEAVEN(S) AND PARADISE - THE DIFFERENCEhttp://quransmessage.com/articles/heaven%20and%20paradise%20FM3.htm[2] ARE THERE SEVEN HEAVENS OR SEVERAL HEAVENS?http://quransmessage.com/articles/are%20there%20seven%20heavens%20or%20several%20heavens%20FM3.htm