REVIEW 3 major objections 3 minor 25 references
NewtonGS: Physics-Structured Object-Level Neural Newtonian Dynamics for Gaussian Scene Animation
T0 review · 3 major / 3 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read NewtonGS proposes that animating a static Gaussian scene reduces to rolling out one 22-dimensional physical state per object and applying the predicted pose and scale as a shared affine transform to all object Gaussians.
desk verdict Solid, honest systems integration, but the ID leg of the headline claim is selected on the test set; the OOD leg holds and the architecture is still worth referee time. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is Gaussian Neural Newtonian Dynamics (Gaussian-NND), a 22-dimensional state per object combined with a continuous analytic prior, zero-initialized neural residuals, and a discrete contact map. The state's variables are chosen so that the same numbers that drive the ODE also define a deterministic affine map for all Gaussians in the object, separating translation, rotation, and anisotropic scale while preserving covariance positive semidefiniteness. RK4 integrates the hybrid field; a floor event outside the continuous solver handles instantaneous velocity changes. This machinery is what lets the model predict one trajectory per object rather than one trajectory per Gaussian primitive.
What would settle it
On a held-out set of real reconstructed Gaussian objects with automatically lifted states, compare NewtonGS's trajectory RMSE against the best analytic baseline over contact-rich motions; if the hybrid's advantage is not reproduced or the lifted states are unstable, the paper's central claim would be refuted. A more direct check is to feed the model a real video with unknown object state and see whether the predicted 22-dimensional rollout matches the observed motion.
Extended reading notes
Core claim
The paper's central claim is that a physics-structured hybrid is the right way to predict object-level motion for Gaussian animation: fixed analytic dynamics alone underfit the synthetic motion families, while an unstructured network would sacrifice interpretability and control. Gaussian-NND therefore writes state evolution as a structured ODE with $\dot p=v$, $\dot q=\tfrac12 q\otimes[0,\omega]$, gravity and damping in $\dot v$, scale restoration in $\dot u$, and a discontinuous horizontal-floor event that applies restitution and tangential attenuation, with learned residual terms $r_v,r_\omega,r_s$ and an impulse correction $\Delta v,\Delta\omega$ added at contacts. The predicted pose and scale are converted to a relative rotation-and-scale matrix $A_t=R(q_t\otimes q_0^*)\operatorname{diag}(s_t\oslash s_0)$, and every Gaussian of the object updates as $g_i^t=A_t(g_i^0-p^0)+p^t$, $\Sigma_i^t=A_t\Sigma_i^0A_t^\top$. The reported experiments show lower trajectory RMSE, final-displacement error, and velocity RMSE than five analytic baselines on State-32's in-distribution and velocity-range-shift splits, with the explicit caveat that these evaluations start from labeled initial states and do not test observation-to-state inference.
Load-bearing premise
The headline numbers come from procedurally generated trajectories with the true initial state handed to the model, so the central premise is that such labeled object states—or a lifting procedure that recovers them—are available for real Gaussian objects.
Editorial extensions
If this is right
- Users could animate a reconstructed Gaussian object by editing roughly ten physical quantities—position, velocity, scale, mass, restitution, and friction—instead of specifying per-Gaussian motion.
- Because the dynamics cost is independent of the Gaussian count, scenes with millions of primitives remain animatable with the same learned model.
- The zero-initialized residual design gives a safe default: before learning, the rollout is exactly the analytic physics prior, so failures can be attributed to the prior rather than to a black-box network.
- The rotation-and-scale affine update keeps covariance matrices valid, so rendered primitives stay coherent under large predicted motion.
- The velocity-range-shift results suggest the learned corrections are not merely memorizing training speeds, although the benchmark remains synthetic.
Reading between the lines
- Editorial inference: if the same hybrid is applied to real reconstructed scenes, its success will hinge on the state-lifting step; the paper's own appendix flags that PCA lifting can flip axes or leak masks, so a natural test is to measure how much of the State-32 advantage survives automatic lifting.
- Editorial inference: the 22-dimensional state could be extended to multi-object interaction by replacing the single floor event with pairwise contact and broad-phase collision, which the current model explicitly excludes.
- Editorial inference: since State-32 targets are generated from closed-form formulas, a stronger stress test is to train the same architecture on a simulator with contact-rich, articulated, or non-analytic dynamics and compare against the analytic prior; the paper lists real scenes as future work.
- Editorial inference: the shared affine transform means 'non-rigid deformation' in the benchmark covers only aggregate anisotropic scaling, so a genuine deformation field would require a larger state or per-part transforms.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces NewtonGS, a framework for object-level animation of static 3D Gaussian scenes. Each object is assigned a 22-dimensional dynamic state (position, quaternion orientation, linear/angular velocity, anisotropic scale and its rate, mass, restitution, and tangential attenuation). A structured hybrid model, Gaussian-NND, combines analytic translation, quaternion kinematics, gravity, damping, and scale-restoration dynamics with learned continuous and contact residuals; floor contact is treated as a discrete event. Predicted states are mapped back to Gaussian primitives through a shared affine transformation. The method is evaluated on two procedurally generated datasets: State-32 for state rollout and Gaussian-32 for state-to-Gaussian conversion. The main empirical claim is that NewtonGS achieves lower trajectory RMSE, final displacement error, and velocity RMSE than five analytic baselines on both the in-distribution and velocity-range-shift splits of State-32.
Significance. If the headline results survive scrutiny, the paper makes a useful contribution: it offers a compact, controllable object-level state for Gaussian scene animation and shows that a hybrid analytic-plus-residual dynamics model can outperform hand-specified analytic baselines on a large procedural benchmark. The manuscript is unusually transparent: it reports three-seed runs with small standard deviations, provides full procedural-generator specifications and exact evaluation formulas in the appendix, and candidly documents failure modes and the observation-to-state gap in Appendix G. These strengths are substantial. The main caveats are that the reported improvements over baselines are modest (roughly 2 to 5 percent relative error reduction), the comparison set contains no learned non-physics baseline, and the in-distribution evaluation is compromised by the checkpoint-selection protocol described in Appendix B.2. The real-scene gap is acknowledged by the authors and is not, by itself, a fatal flaw.
major comments (3)
- [Appendix B.2 / §4.2] Appendix B.2 states that "val_id and val_ood are exactly the ID and OOD test sets reported in the main paper" and that "Model selection uses the complete val_id objective," and Appendix A.6 confirms that the best checkpoint is selected by that objective. Because the ID rows of Table 1 are computed on val_id, the in-distribution half of the abstract's claim is a test-set-selected number rather than an out-of-sample result: the checkpoint is chosen to minimize the loss on the very sequences used to compute the reported ID metrics. This is a load-bearing methodological problem. Please introduce a genuine validation split disjoint from both test splits, select checkpoints on it, and re-report Table 1. The OOD comparison, which is not used for selection, remains informative.
- [Eq. (8) vs. Appendix A.4, Eq. (19)] The main-text affine map in Eq. (8), A_t = R_t diag(rho_t) R_0^T, is not the transform implemented in Appendix A.4, Eq. (19), Aimpl_t = R(q_t ⊗ q*_0) diag(rho_t). These coincide only for q0 = I or isotropic scale; for a general initial orientation they differ because the scale is applied in different frames. Since the state-to-Gaussian conversion is a stated contribution and is used in the Gaussian-32 experiments, the paper should either report results using the Eq. (8) transform or explicitly adopt the implemented version in the main text and explain the discrepancy.
- [§4.4 and Conclusion] The experiments compare NewtonGS only with hand-specified analytic baselines; no learned, non-physics baseline is trained on the same data and loss, and the paper itself lists "learned baselines" as future work. Because a central motivation is that the physics structure improves learned dynamics, a feedforward or recurrent trajectory model of comparable capacity is needed to establish that the structured prior, rather than the neural residual alone, is responsible for the reported gains. The post-hoc branch removal in Table 14 does not answer this question, since the remaining model is not independently trained without the branch.
minor comments (3)
- [Appendix B.4 / Table 3] Appendix B.4 states that the Common-12 manifest contains 84 videos across seven methods, but Table 3 reports results for only five methods. Please either include the CogVideoX and NewtonGen rows or explicitly state why they are omitted from the table.
- [§3.5] The sentence "The smoothness term penalizes Lpen second temporal differences of position and, with relative weight 0.1, scale" is garbled; it should read something like "The smoothness term penalizes second temporal differences of position and, with relative weight 0.1, scale, and is included in Lsmooth."
- [Table 2 caption] The caption describes the comparison as "exploratory" and notes that L4GM receives different inputs, which is appropriate; consider adding a sentence in the main text of §4.6 clarifying that the velocity comparison is not a controlled same-input comparison.
Circularity Check
The in-distribution leg of the headline result is selected on the test set: val_id is both the model-selection set and the reported ID test set, so the ID claim is not an out-of-sample prediction.
-
fitted input called prediction
[Appendix B.2 (State-32) and Appendix A.6, Table 4 (Checkpointing)]
"The executed corpus contains exactly three partitions named train, val_id, and val_ood. The val prefix is an implementation-level filename retained for compatibility: val_id and val_ood are exactly the ID and OOD test sets reported in the main paper, rather than validation subsets in addition to a missing test set. Both are generated independently of and are disjoint from the training set. Model selection uses the complete val_id objective, and the reported ID and velocity-shift results are evaluations on val_id and val_ood, respectively; val_ood is not used for checkpoint selection."
Table 1's ID rows report trajectory, FDE, and velocity errors computed on val_id, but Appendix A.6/Table 4 states that checkpoints are saved at epoch 1 and every 5 epochs and that the 'best checkpoint selected by the complete val_id objective.' The reported ID numbers are therefore the result of selecting the model on the same sequences used to produce those very metrics. The abstract's conjunctive claim of lower errors 'on both the in-distribution and velocity-range-shift splits' has one leg that is a selected, not predicted, outcome; the checkpoint is fitted to the ID test set by the paper's own protocol. The OOD leg remains valid because val_ood is explicitly not used for checkpoint selection.
full rationale
The state-rollout derivation itself is self-contained: Gaussian-NND is a supervised hybrid model trained on labeled State-32 sequences, the analytic prior and zero-initialized residuals are stated explicitly, and the state-to-Gaussian map is a deterministic affine transform rather than a fitted prediction. Citations to NewtonGen and other prior work are motivational and not load-bearing, and no uniqueness theorem or self-citation chain is used to force the architecture or the comparison. The only circular element is the ID evaluation protocol: Appendix B.2 discloses that val_id is exactly the reported ID test set and that model selection uses the complete val_id objective, so the ID rows of Table 1 are selected on the test set rather than out-of-sample. Appendix G candidly concedes the observation-to-state gap and the synthetic-data scope, and the Common-12 and L4GM tables are labeled proxy or interface checks, so those limitations are acknowledged rather than hidden. Because one of the two conjunctive legs of the headline claim is compromised by construction while the OOD leg and the core learning formulation retain independent content, the appropriate score is 6.
Assumptions & free parameters
free parameters (4)
- cv, c_omega, k_s, c_s, alpha, alpha_imp =
trained, final values not reported; initial values 0.05, 0.05, 0.25, 0.08, 0.01, 0.01
- Neural residual weights of f_theta and h_phi =
81,429 trainable parameters total
- Loss weights in Eq. 10 and Eq. 11 =
1.0, 0.25, 0.5, 0.2, 0.2, 0.1, 0.0, 0.05, 0.01
- RK4 substep maximum =
1/30 s, giving two 1/48 s substeps per 24 Hz frame
assumptions (6)
- standard math Quaternion kinematics: dq/dt = (1/2) q ⊗ [0, omega]
- ad hoc to paper Floor contact is a horizontal plane y=0 with vertical extent proxy r_y = max(|s_y|, 1e-3)
- domain assumption All Gaussians of an object move by the same affine map A_t = R_t diag(rho_t) R_0^T
- ad hoc to paper Scale-restoration dynamics: u_dot = -|k_s|(s-1) - |c_s|u + alpha r_s
- domain assumption Material channels (m, e, mu) are constant during rollout and supplied with the initial state
- ad hoc to paper State-32 generator equations define the ground-truth target dynamics
Cite this review
Pith. "Pith review of NewtonGS: Physics-Structured Object-Level Neural Newtonian Dynamics for Gaussian Scene Animation." pith.science (2026). https://pith.science/paper/IKLNSGIP
@misc{pith2026260807598,
author = {Pith},
title = {Pith review of: NewtonGS: Physics-Structured Object-Level Neural Newtonian Dynamics for Gaussian Scene Animation},
year = {2026},
howpublished = {\url{https://pith.science/paper/IKLNSGIP}},
note = {Machine review of arXiv:2608.07598}
}
read the original abstract
Animating objects in a static 3D Gaussian scene requires an explicit object-level dynamic state and a controllable model of object motion. Existing dynamic Gaussian methods primarily reconstruct time-varying scenes or simulate deformation, rather than provide compact object states for direct control. To address this gap, we present NewtonGS, a physics-structured framework for object-level state rollout and Gaussian scene animation. NewtonGS represents each object with a 22-dimensional state covering pose, linear and angular velocity, anisotropic scale and its rate, mass, and contact properties. Its Gaussian Neural Newtonian Dynamics (Gaussian-NND) model combines analytic translation, quaternion kinematics, gravity, damping, and scale-restoration dynamics with learned continuous and contact residuals. A discrete event map handles floor contact. Predicted poses and scales define a shared affine transformation that updates the means and covariances of all Gaussians associated with each object. We construct two procedurally generated datasets: State-32 for state-rollout evaluation and Gaussian-32 for state-to-Gaussian transformation. On both the in-distribution and velocity-range-shift splits of State-32, NewtonGS achieves lower trajectory RMSE, final displacement error, and velocity RMSE than five analytic baselines. Experiments on Gaussian-32 further demonstrate effective conversion from predicted states to animated Gaussian objects.
Figures
Figures from the paper (12 more)
Reference graph
Works this paper leans on
-
[8]
Yuchen Lin, Chenguo Lin, Jianjin Xu, and Yadong Mu
doi: 10.1109/CVPR52729.2023.00037. Yuchen Lin, Chenguo Lin, Jianjin Xu, and Yadong Mu. OmniPhysGS: 3d constitutive gaussians for general physics- based dynamics generation.arXiv preprint arXiv:2501.18982,
arXiv 2023
-
[9]
Huan Ling, Seung Wook Kim, Antonio Torralba, Sanja Fidler, and Karsten Kreis
doi: 10.48550/arXiv.2501.18982. Huan Ling, Seung Wook Kim, Antonio Torralba, Sanja Fidler, and Karsten Kreis. Align your gaussians: Text-to-4d with dynamic 3d gaussians and composed diffusion models. InProceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition,
-
[11]
Qiaowei Miao, Jinsheng Quan, Kehan Li, and Yawei Luo
doi: 10.1109/3DV62453.2024.00044. Qiaowei Miao, Jinsheng Quan, Kehan Li, and Yawei Luo. PLA4D: Pixel-level alignments for text-to-4d gaussian splatting.arXiv preprint arXiv:2405.19957,
arXiv 2024
-
[12]
Ben Poole, Ajay Jain, Jonathan T
doi: 10.48550/arXiv.2405.19957. Ben Poole, Ajay Jain, Jonathan T. Barron, and Ben Mildenhall. DreamFusion: Text-to-3d using 2d diffusion.arXiv preprint arXiv:2209.14988,
-
[14]
doi: 10.48550/arXiv.2312.17142. Jiawei Ren, Kevin Xie, Ashkan Mirzaei, Hanxue Liang, Xiaohui Zeng, Karsten Kreis, Ziwei Liu, Antonio Torralba, Sanja Fidler, Seung Wook Kim, and Huan Ling. L4GM: Large 4d gaussian reconstruction model. InAdvances in Neural Information Processing Systems, volume 37,
-
[16]
doi: 10.48550/arXiv.2503.20314. Guanjun Wu, Taoran Yi, Jiemin Fang, Lingxi Xie, Xiaopeng Zhang, Wei Wei, Wenyu Liu, Qi Tian, and Xinggang Wang. 4d gaussian splatting for real-time dynamic scene rendering. InProceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition,
-
[18]
doi: 10.1109/CVPR52733.2024.00420. Yinghao Xu, Zifan Shi, Yifan Wang, Hansheng Chen, Ceyuan Yang, Sida Peng, Yujun Shen, and Gordon Wetzstein. GRM: Large gaussian reconstruction model for efficient 3d reconstruction and generation. InEuropean Conference on Computer Vision,
arXiv 2024
-
[19]
Qiyao Xue, Xiangyu Yin, Boyuan Yang, and Wei Gao
doi: 10.1007/978-3-031-72633-0_1. Qiyao Xue, Xiangyu Yin, Boyuan Yang, and Wei Gao. PhyT2V: Llm-guided iterative self-refinement for physics- grounded text-to-video generation. InProceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pp. 18826–18836,
Show all 25 references
-
[20]
Zeyu Yang, Zijie Pan, Xiatian Zhu, Li Zhang, Jianfeng Feng, Yu-Gang Jiang, and Philip H
doi: 10.1109/CVPR52734.2025.01754. Zeyu Yang, Zijie Pan, Xiatian Zhu, Li Zhang, Jianfeng Feng, Yu-Gang Jiang, and Philip H. S. Torr. 4d gaussian splatting: Modeling dynamic scenes with native 4d primitives.arXiv preprint arXiv:2412.20720,
2025
-
[21]
Vickie Ye, Ruilong Li, Justin Kerr, Matias Turkulainen, Brent Yi, Zhuoyang Pan, Otto Seiskari, Jianbo Ye, Jeffrey Hu, Matthew Tancik, and Angjoo Kanazawa
doi: 10.48550/arXiv.2412.20720. Vickie Ye, Ruilong Li, Justin Kerr, Matias Turkulainen, Brent Yi, Zhuoyang Pan, Otto Seiskari, Jianbo Ye, Jeffrey Hu, Matthew Tancik, and Angjoo Kanazawa. gsplat: An open-source library for gaussian splatting.Journal of Machine Learning Research...
-
[22]
Splat4D: Diffusion-enhanced 4d gaussian splatting for temporally and spatially consistent content creation.arXiv preprint arXiv:2508.07557,
Minghao Yin, Yukang Cao, Songyou Peng, and Kai Han. Splat4D: Diffusion-enhanced 4d gaussian splatting for temporally and spatially consistent content creation.arXiv preprint arXiv:2508.07557,
-
[23]
2508.07557
doi: 10.48550/arXiv. 2508.07557. Yu Yuan, Xijun Wang, Tharindu Wickremasinghe, Zeeshan Nadir, Bole Ma, and Stanley H. Chan. NewtonGen: Physics- consistent and controllable text-to-video generation via neural newtonian dynamics. InInternational Conference on Learning Representations,
-
[24]
11 Appendix This appendix is organized as follows
doi: 10.1007/978-3-031-72627-9_22. 11 Appendix This appendix is organized as follows. • Section Adocuments the model objective, state conventions, Gaussian transformation, initialization, optimiza- tion, evaluation, and inference. • Section Bspecifies the Gaussian-32 evaluatio...
-
[25]
The loader accepts a tensor of shape (T, C)or (B, T, C), where B is batch size, T is the number of timestamps, and C is the number of supplied channels. It adds a batch dimension when necessary, retains the first 22 channels, converts the result to contiguous float32, and perf...
1993
-
[26]
Neither renderer affects the state metrics
or the lightweight fallback. Neither renderer affects the state metrics. B Dataset Construction This section defines four data resources in order. Gaussian-32 is the appearance-conditioned Gaussian evaluation set; State-32 is the procedural state-trajectory corpus; Same-32 is ...
2026
-
[27]
The vectors p,v,s,u∈R 3 are position, velocity, scale, and scale rate
(28) Here t≥0 is elapsed time; subscripts 0 and t denote initial and current quantities. The vectors p,v,s,u∈R 3 are position, velocity, scale, and scale rate. The first line integrates constant linear velocity. The second line integrates constant scale rate and then applies m...
-
[1985]
Jiaxiang Tang, Zhaoxi Chen, Xiaokang Chen, Tengfei Wang, Gang Zeng, and Ziwei Liu
doi: 10.1145/325334.325242. Jiaxiang Tang, Zhaoxi Chen, Xiaokang Chen, Tengfei Wang, Gang Zeng, and Ziwei Liu. LGM: Large multi-view gaussian model for high-resolution 3d content creation. InEuropean Conference on Computer Vision, 2024a. doi: 10.1007/978-3-031-73235-5_1. Jiaxi...
-
[1993]
doi: 10.1007/978-3- 540-78862-1. I. T. Jolliffe.Principal Component Analysis. Springer Series in Statistics. Springer, New York, 2 edition,
-
[2002]
Bernhard Kerbl, Georgios Kopanas, Thomas Leimkühler, and George Drettakis
doi: 10.1007/b98835. Bernhard Kerbl, Georgios Kopanas, Thomas Leimkühler, and George Drettakis. 3d gaussian splatting for real-time radiance field rendering.ACM Transactions on Graphics, 42(4),
-
[2019]
Physion: Evaluating physical prediction from vision in humans and machines.arXiv preprint arXiv:2106.08261,
Daniel M Bear, Elias Wang, Damian Mrowca, Felix J Binder, Hsiao-Yu Fish Tung, RT Pramod, Cameron Holdaway, Sirui Tao, Kevin Smith, Fan-Yun Sun, et al. Physion: Evaluating physical prediction from vision in humans and machines.arXiv preprint arXiv:2106.08261,
-
[2020]
Yunze Deng, Haijun Xiong, Bin Feng, Xinggang Wang, and Wenyu Liu
doi: 10.48550/arXiv.2003.04630. Yunze Deng, Haijun Xiong, Bin Feng, Xinggang Wang, and Wenyu Liu. STP4D: Spatio-temporal-prompt consistent modeling for text-to-4d gaussian splatting. InIEEE International Conference on Multimedia and Expo,
-
[2021]
Spergel, and Shirley Ho
Miles Cranmer, Sam Greydanus, Stephan Hoyer, Peter Battaglia, David N. Spergel, and Shirley Ho. Lagrangian neural networks.arXiv preprint arXiv:2003.04630,
2003 arXiv
- [2022]
-
[2023]
Chen-Hsuan Lin, Jun Gao, Luming Tang, Towaki Takikawa, Xiaohui Zeng, Xun Huang, Karsten Kreis, Sanja Fidler, Ming-Yu Liu, and Tsung-Yi Lin
doi: 10.1145/3592433. Chen-Hsuan Lin, Jun Gao, Luming Tang, Towaki Takikawa, Xiaohui Zeng, Xun Huang, Karsten Kreis, Sanja Fidler, Ming-Yu Liu, and Tsung-Yi Lin. Magic3D: High-resolution text-to-3d content creation. InProceedings of the IEEE/CVF Conference on Computer Vision a...
-
[2025]
Xavier Glorot and Yoshua Bengio
doi: 10.1109/ICME59968.2025.11209788. Xavier Glorot and Yoshua Bengio. Understanding the difficulty of training deep feedforward neural networks. InProceedings of the Thirteenth International Conference on Artificial Intelligence and Statistics, volume 9 of Proceedings of Mach...
2025
Reviewed August 11, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.