宇宙膨脹與引力勢能問題

[WFPC2]

...
technically you can't say about Kinetic energy in terms of GR as well...becoz' the clock and ruler are changing....

If this is true, why I can find formula of KE for SR?

SR =/= GR ar ma =.="""

indeed, SR is just a special case in GR...

That's exactly what I'm thinking.
Why we can't define(?) KE in GR but can in SR? It doesn't make sense...

因爲之前己說過太空船的K.E己化為能量-動量張量的描述,只有能量動量-動張量是守恆的。

[Wah!!]

...
technically you can't say about Kinetic energy in terms of GR as well...becoz' the clock and ruler are changing....

If this is true, why I can find formula of KE for SR?

SR =/= GR ar ma =.="""

indeed, SR is just a special case in GR...

That's exactly what I'm thinking.
Why we can't define(?) KE in GR but can in SR? It doesn't make sense...

因爲之前己說過太空船的K.E己化為能量-動量張量的描述,只有能量-動張量是守恆的。

這里我不是問KE轉成什么, 而是問為什么 quantumkit 說 "technically you can't say about Kinetic energy in terms of GR" 的同時, 我會找到 SR 中的 KE 公式.

[WFPC2]

引力波帶走的能量, 即使在互繞中子星之間也是比其他形式的能量少很多很多的, 否則科學家也不會費盡心思去測量它.

所以我同意 quantumkit 的看法, 不必用引力波考慮太空船飛離地球時的動能跑到哪里去.

引力波的確只佔很少,中子星發出引力波只因距離遙遠而以距離平方反比減弱,若在中子星對在你附近發碰撞,你就看得見引力波的影響。

[sptfung]

...
technically you can't say about Kinetic energy in terms of GR as well...becoz' the clock and ruler are changing....

If this is true, why I can find formula of KE for SR?

SR =/= GR ar ma =.="""

indeed, SR is just a special case in GR...

That's exactly what I'm thinking.
Why we can't define(?) KE in GR but can in SR? It doesn't make sense...

......why physical laws has to obey the "sense" of human?
you have to understand science concept is not equal to the truth

[sptfung]

Conservation of energy-momentum tensor is the ONLY conservation law in GR.
you are using old concepts that you hope that would fit into a new theory.
it is just like you ask: why we can define "ether" in Newtonian, but not in relativity? note that Newtonian is ALSO A SPECIAL CASE of relativity.

[sptfung]

how could one define "sense"?
what is the criteria for a theory is making any "sense"?

if you cannot answer these questions, i cannot see the logic why you so insist to define everything in GR such that they can "make the sense"...

[sptfung]

可能 "energy-momentum tensor" 呢個term 誤導左你
等你以為只係將以前既 energy 同 momentum 放在一起而已

實際上，energy-momentum tensor 係一種新既 concept
o係四維時空入面，energy-momentum tensor 係講緊十六個量
只不過o係某 d special case 入面我地的確可以分辨到某 d 量同我地以往o既 energy 同 momentum 類似，故得其名

你問我咩係 energy-momentum tensor ，就正如問我咩係 wave-particle (或者 particle-wave) 一樣：who knows?

[WFPC2]

可能 "energy-momentum tensor" 呢個term 誤導左你
等你以為只係將以前既 energy 同 momentum 放在一起而已

實際上，energy-momentum tensor 係一種新既 concept
o係四維時空入面，energy-momentum tensor 係講緊十六個量
只不過o係某 d special case 入面我地的確可以分辨到某 d 量同我地以往o既 energy 同 momentum 類似，故得其名

你問我咩係 energy-momentum tensor ，就正如問我咩係 wave-particle (或者 particle-wave) 一樣：who knows?

Anyway,K.E 不能defined在廣義相對論的範疇內,是否因為K.E己被簡化為時空的曲率張量,像視重力為時空的幾何結構造成般,物體被加速獲得動能一律被視為彎曲四維時空的實體?

[quantumkit]

...
technically you can't say about Kinetic energy in terms of GR as well...becoz' the clock and ruler are changing....

If this is true, why I can find formula of KE for SR?

SR =/= GR ar ma =.="""

indeed, SR is just a special case in GR...

That's exactly what I'm thinking.
Why we can't define(?) KE in GR but can in SR? It doesn't make sense...

因爲之前己說過太空船的K.E己化為能量-動量張量的描述,只有能量-動張量是守恆的。

這里我不是問KE轉成什么, 而是問為什么 quantumkit 說 "technically you can't say about Kinetic energy in terms of GR" 的同時, 我會找到 SR 中的 KE 公式.

The formula for KE in SR is ONLY an analogy to the Newtonian case. We have mass energy, E=mc^2 and total energy (when moving) E = sqrt( m^2c^4 + p^2 c^2 )...and then people "say" (without gravity here..)

KE = total energy - rest mass energy

= sqrt ( m^2c^4 + p^2 c^2 ) - mc^2

which becomes p^2 / (2m) for small momentum p in Newtonian case.

[quantumkit]

可能 "energy-momentum tensor" 呢個term 誤導左你
等你以為只係將以前既 energy 同 momentum 放在一起而已

實際上，energy-momentum tensor 係一種新既 concept
o係四維時空入面，energy-momentum tensor 係講緊十六個量
只不過o係某 d special case 入面我地的確可以分辨到某 d 量同我地以往o既 energy 同 momentum 類似，故得其名

你問我咩係 energy-momentum tensor ，就正如問我咩係 wave-particle (或者 particle-wave) 一樣：who knows?

Anyway,K.E 不能defined在廣義相對論的範疇內,是否因為K.E己被簡化為時空的曲率張量,像視重力為時空的幾何結構造成般,物體被加速獲得動能一律被視為彎曲四維時空的實體?

I guess not, but I am not sure if you are really wrong...haha

You can always have a mass-less (or small mass) test particle moving in a curved spacetime (e.g. near the sun), without affecting the curvature at all.

[WFPC2]

Conservation of energy-momentum tensor is the ONLY conservation law in GR.
you are using old concepts that you hope that would fit into a new theory.
it is just like you ask: why we can define "ether" in Newtonian, but not in relativity? note that Newtonian is ALSO A SPECIAL CASE of relativity.

可能 "energy-momentum tensor" 呢個term 誤導左你
等你以為只係將以前既 energy 同 momentum 放在一起而已

實際上，energy-momentum tensor 係一種新既 concept
o係四維時空入面，energy-momentum tensor 係講緊十六個量
只不過o係某 d special case 入面我地的確可以分辨到某 d 量同我地以往o既 energy 同 momentum 類似，故得其名

你問我咩係 energy-momentum tensor ，就正如問我咩係 wave-particle (或者 particle-wave) 一樣：who knows?

根據你對energy -momentum tensor的描述,這又不見得是一個
Old Concept Wor!

Particle -wave 咪即係機率波,機率的波涵數訴告訴你關於粒子出現各
狀態的機率如位置,動量,自旋.....等等lor

同理我幾時問過你這堆問題呢?科學只能說關於世界我們可以討論甚麼,不能
知道世界真正是甚麼,但盡量可以用一組定律去簡化自然界的各種複雜的現象。

牛頓力學怎會是相對論的特例?牛頓力學忽略了光速,在力學的描述亦與相對論不同,只能說它在弱重力場和低速的情況下,描述與相對論差別不大,不過牛頓的引力常數G仍懸用在相對論的上,狹義相對論則未能處理重力的問題,因為狹義相對論是平直的時空。

how could one define "sense"?
what is the criteria for a theory is making any "sense"?

if you cannot answer these questions, i cannot see the logic why you so insist to define everything in GR such that they can "make the sense"...

呢個好以回應緊Wah!的問題,抑或指以科學角度去定義「人類意識」的
問題呢?

[Wah!!]

若 energy-momentum tensor 是經典物理中的 energy, momentum 等物理量炒埋一碟的新名詞.
宇宙膨脹下, 用經典物理看到引力勢能會因而改變.
那麼, 廣義相對論的 energy-momentum tensor 是否應該也會因為宇宙膨脹影響而有所改變呢?
我不知道 energy-momentum tensor 有無大小之分? 若是有, 宇宙膨脹是否會使 energy-momentum tensor 變大?

[WFPC2]

若 energy-momentum tensor 是經典物理中的 energy, momentum 等物理量炒埋一碟的新名詞.
宇宙膨脹下, 用經典物理看到引力勢能會因而改變.
那麼, 廣義相對論的 energy-momentum tensor 是否應該也會因為宇宙膨脹影響而有所改變呢?
我不知道 energy-momentum tensor 有無大小之分? 若是有, 宇宙膨脹是否會使 energy-momentum tensor 變大?

我想應該有了,因為在封閉系統energy-momentum tensor 是一個變量而不是一個常數,但不知是否需要區分"時空曲率"與"曲率張量”?

宇宙的膨脹令時空變得平坦,曲率減少,但我想宇宙的energy-momentum
tensor 應該不變,因為energy -momentum tensor 是守衡的,這沒有理會Dark Energy 和量子力學對真空的描述。

[sptfung]

Conservation of energy-momentum tensor is the ONLY conservation law in GR.
you are using old concepts that you hope that would fit into a new theory.
it is just like you ask: why we can define "ether" in Newtonian, but not in relativity? note that Newtonian is ALSO A SPECIAL CASE of relativity.

可能 "energy-momentum tensor" 呢個term 誤導左你
等你以為只係將以前既 energy 同 momentum 放在一起而已

實際上，energy-momentum tensor 係一種新既 concept
o係四維時空入面，energy-momentum tensor 係講緊十六個量
只不過o係某 d special case 入面我地的確可以分辨到某 d 量同我地以往o既 energy 同 momentum 類似，故得其名

你問我咩係 energy-momentum tensor ，就正如問我咩係 wave-particle (或者 particle-wave) 一樣：who knows?

根據你對energy -momentum tensor的描述,這又不見得是一個
Old Concept Wor!

Particle -wave 咪即係機率波,機率的波涵數訴告訴你關於粒子出現各
狀態的機率如位置,動量,自旋.....等等lor

同理我幾時問過你這堆問題呢?科學只能說關於世界我們可以討論甚麼,不能
知道世界真正是甚麼,但盡量可以用一組定律去簡化自然界的各種複雜的現象。

牛頓力學怎會是相對論的特例?牛頓力學忽略了光速,在力學的描述亦與相對論不同,只能說它在弱重力場和低速的情況下,描述與相對論差別不大,不過牛頓的引力常數G仍懸用在相對論的上,狹義相對論則未能處理重力的問題,因為狹義相對論是平直的時空。

how could one define "sense"?
what is the criteria for a theory is making any "sense"?

if you cannot answer these questions, i cannot see the logic why you so insist to define everything in GR such that they can "make the sense"...

呢個好以回應緊Wah!的問題,抑或指以科學角度去定義「人類意識」的
問題呢?

我都唔係答緊你 =.="""
我答緊Wah!! 之ma =.="""

btw, Special Relativity reduces to Newtonian in small speeds. (v/c <<1)

momentum = gamma mv ~ mv when gamma ~ 1
KE, total energy etc all the same reduces.

[sptfung]

我諗我以後都要 quote 左先答 =.="""