Question: > 
> He is the radiance of the glory of God and the exact imprint of his nature, and he upholds the universe by the word of his power. After making purification for sins, he sat down at the right hand of the Majesty on high (Hebrews 1:3 ESV)
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I am interested in the phrase ‘he upholds the universe’
My question is:- How could Christ uphold the universe as a helpless babe and also after he had died before the resurrection.

Answer: 
One thing is to simply ***be*** helpless babe and another thing is to ***make oneself to be*** a helpless babe. Just as the Lord made Himself to adopt human nature with all its features of need of food, drink, air, feeling of pain etc., so also He made Himself needful also of parental care and caressing. Having put upon Himself voluntarily all human features except for the falledness with its innate sinfulness and proclivity to sin, He put upon Himself also growth from babe-hood to childhood and to adulthood. The same Logos who took upon Himself the babe-hood of His human nature, created the universe together with the Father and always upheld it.

It is simply a complete outlandishness to think that having adopted human nature and having made Himself to be a babe He, the Logos, took vacation from the Father and did not hold the universe into existence together with Him! How long then those vacations lasted? Ten years? Thirteen, before His bar mitzvah? And after that maybe also the Father indulged Himself in going to vacations saying “My dear Son-Logos, for thirteen years I did the job of sustaining the universe alone, now it’s my turn to take some rest, not much, just two-three weeks, I will go hiking outside the universe in company with the H.Ghost not to feel myself alone”. But why to entertain such funny things on this respectable site of the biblical exegesis?

But more seriously, it is a Christological issue: He is the co-eternal and co-unoriginated Son of the Father-God, who "was" with God, that is to say, in infinity, as the *praeteritum imperfectum* of this verb indicates (John 1:1); and as all things are created by Both Father and the Son (ibid. 1:3), so also are sustained through the Father and the Son (and H.Ghost for that matter), (Heb. 1:3), because as Descartes well says in 3rd metaphysical meditation, "sustaining is just another word for creating, for exactly the same amount of energy is exerted for sustaining as for creating".

Therefore, Logos, the Father's co-eternal and co-infinite Son-God ontologically cannot die, not any less than Father cannot die also, for it is impossible for God to die or commit suicide. If Logos or the Father slumber just a second, the world will cease to exist.

Now, Logos adopted human nature and human nature dies. Since this human nature became nature of the Person/Hypostasis of Logos, who also has had divine nature before the incarnation, we can freely say that God-Logos died according to His human nature, that God-Logos suckled breast of his mother, the Virgin Mary, as a child, according to His human nature, but at age 12 was instructing and bewildering expert elderly theologians without having learned the Scripture as God (Luke 2:41-52); getting tired and thirsty according to His human nature, but giving food in desert from two fishes and five breads to five thousands, without counting also women and children, for their full satiation as God (Matthew 14:13:21).

But those questions are so well trodden and this sound Orthodox/Catholic teaching comes from the Ecumenical Council of Chalcedon 451, that stroke a middle ground between heresies of Monophysitism and Nestorianism.
It is impossible to answer this question as we are not told so we cannot know. Indeed, if we knew the answer to this question, we would be God.

Equally mysterious, is the the fact that

* twice in the Gospel of John, we are told the Jesus raised Himself from the dead, John 2:19-21 and 10:17, 18.
* However, we are also told that the Father raised Jesus from the dead as well, Rom 6:4, Gal 1:1, Eph 1:17-20.
* Further, we are also told that the Holy Spirit is the source of life as well, Rom 1:4 & 8:11, 1 Peter 3:18.
* Acts 2:24, 3:15, 4:10, 5:30, 10:40, 13:30, 17:31, Rom 4:24, 1 Cor 15:15, Col 2:20, Heb 13:20, 1 Peter 1:3, 1 Thess 1:10 simply say that “God” raised Jesus without specifying any specific member of the Godhead.

All this simply illustrates the fact that the Godhead acts in complete unison. Just how that occurs we are not told. The same is presumably true of God upholding the universe.